Life cycle variation and adaptation in jumping plant lice (Insecta ...

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Journal of Natural History 

Vol. 43, Nos. 1–2, January 2009, 65–179 

Life cycle variation and adaptation in jumping plant lice (Insecta: 

Hemiptera: Psylloidea): a global synthesis 

Ian D. Hodkinson* 

School of Biological and Earth Sciences, Liverpool John Moores University, Liverpool, UK 

(Received 1 February 2008; final version received 20 July 2008) 

This paper integrates the scattered information on the life histories of the jumping 

plant lice or psyllids, examining those aspects of their biology that contribute to 

successful life cycle completion. Variation in life history parameters is reviewed 

across the world’s psyllids and the relative importance of phylogeny and 

environment, including host-plant growth strategy, in determining life history 

strategies is assessed. Elements of life cycles considered include: development rate 

and voltinism, response to high temperature and drought, cold-hardiness and 

overwintering strategy, seasonal polymorphism, diapause, metabolism, host-plant 

selection and range, phenological and other adaptations to host plants, disease 

transmission and host amelioration, dispersal, reproduction and mate finding. 

Life history parameters are analyzed for 342 species. While a phylogenetic signal 

can be identified within the data, the main drivers for life history adaptation are 

environmental temperatures and water availability, acting directly on the psyllids 

or mediated through their host plants. 

Keywords: psyllid; life-history; phylogeny; temperature; water 

Introduction 

Jumping plant lice, or psyllids (Psylloidea), comprise a group of around 3000 species 

of small plant-sap-feeding insects allied to the aphids and whiteflies. They occur 

throughout nearly all the world’s major climatic regions where suitable host plants 

are found. This paper attempts to integrate the wealth of scattered information on 

the life histories of the psyllids and to examine those aspects of their biology that 

contribute to successful life cycle completion. A significant proportion of this 

information is contained in relatively old or obscure sources, or is to be found in 

current literature that escapes electronic abstracting and is thus in increasing danger 

of remaining unrecognized. The broad variations that occur within psyllid life cycles 

are documented and the modifications of biology and mechanisms by which psyllids 

adapt to exploit a diverse range of host plants growing under varying environmental 

conditions are examined. An attempt is made throughout to identify common 

themes and patterns. Table 1 draws together, in taxonomic sequence, the basic data 

and reference sources that are avilable for the life histories of the world’s Psylloidea 

species and this forms the foundation for the subsequent analyses. 

The great majority of psyllid species are narrowly host-specific and are 

predominantly associated with perennial dicotyledenous angiosperms 

(Klimaszewski 1973; Hodkinson and White 1981; Hodkinson 1983a, 1986a, 1988a; 

Gegechkori and Loginova 1990; Hollis 2004). A few species develop on monocots 

*Email: i.d.hodkinson@ljmu.ac.uk 

ISSN 0022-2933 print/ISSN 1464-5262 online 

# 2009 Taylor & Francis 

DOI: 10.1080/00222930802354167 

http://www.informaworld.com


66 I.D. Hodkinson 

including Livia spp. on Carex and Juncus, Bactericera tremblayi (Wagner) and B. 

kratochvili (Vondracek) on Allium spp. (Alliaceae), and a few species on Palmaceae. 

These include an undescribed species on Bactris gasipaes in Colombia, five Hawaiian 

Megatrioza on Pritchardia, an undescribed Australian paurocephaline species on 

Livistona and an undescribed Indian ‘‘Psylla’’ species on Areca catechu 

(Klimaszewski 1973; Pava et al.1983; Uchida and Beardsley 1988; Hodkinson and 

Bird 2000; Mondal et al. 2003; Hollis 2004). Gymnosperms are similarly poorly 

exploited as host plants, with just two species of Ehrendorferiana Burckhardt 

breeding on Austrocedrus and Fitzroya (Cupressaceae) in Chile and Trioza colorata 

Ferris and Klyver and T. dacrydii Tuthill exploiting Dacrydium (Podocarpaceae) in 

New Zealand (Tuthill 1952; Burckhardt 2005a). Conifers, however, as discussed 

later, play a highly significant role as overwintering shelter plants for adults from a 

wide range of psyllid species. 

The psyllid life cycle typically comprises of an egg stage, five larval instars and a 

sexually reproducing adult stage, with males and females usually showing only 

moderate deviation from a 1:1 sex ratio at emergence. Parthenogenetic reproduction, 

in which only females are found in the population, is rare but probably occurs in 

some populations of Cacopsylla rara (Tuthill), Glycaspis operta (Moore), Glycaspis 

atkinsoni Moore and Cacopsylla myrtilli (Wagner) (Hodkinson 1983b; Moore 1983; 

Hodkinson and Bird 2006a). The latter species appears as populations of 

parthenogenetic females throughout most of its circumboreal range but males 

become common at higher altitudes above tree line (Hodkinson and Bird 2006a). 

Within the equitable warm and wet conditions of lowland tropical evergreen 

rainforests psyllid life cycles tend to be continuous, with multiple generations per 

year. This probably typifies the environment under which psyllids originally 

radiated. This continuous multivoltine life cycle – appropriate to a climatically 

benign environment – has, however, subsequently undergone considerable modification. 

Psyllids have adapted to exploit a range of host plants that have themselves, 

over evolutionary time, diversified their physiognomy, physiology and phenology as 

they adapted to varying environmental conditions within widely different major 

climatic zones. Such evolution is driven by two overriding variables, temperature and 

precipitation, which vary in response to site latitude, altitude and continentality. 

Host plants have also undergone concomitant chemical evolution and adaptation 

during which their unique chemistry, in particular their complement of characteristic 

secondary compounds, has evolved. This unique chemistry is thought to form the 

basis for host selection and host fidelity in the psyllids. 

In the only detailed study of psyllid plant coevolution, involving host-specific 

legume feeding psyllids on the Canary Islands, .60% of host associations resulted 

from phylogenetically conserved host switching among related legumes: strict 

cospeciation was only evident among more recent psyllid–host associations (Percy 

2003a, 2003b; Percy et al. 2004). Thus, while precise evolutionary tracking of host 

plants may not always have occurred, related groups of psyllids tend usually to be 

typically associated with related host-plant taxa and individual psyllid species, with a 

few notable exceptions, display a high degree of host specificity (Hodkinson 1974, 

1986b; van Klinken 2000). The exceptions are usually north temperate multivoltine 

pest species such as Bactericera nigricornis, B. trigonica Hodkinson and B. cockerelli 

feeding variously on a range of host-plant genera within the Solanaceae, 

Umbelliferae and Cruciferae (Pletsch 1947; Wallis 1955; Hodkinson 1981). Some


Journal of Natural History 67 

species that were initially thought to be polyphagous, such as the univoltine Trioza 

rotundata in Europe (on Stellaria (Caryophyllaceae), Saxifraga (Saxifragaceae) and 

Cardamine (Cruciferae), (Conci and Tamanini 1987, 1991)) have subsequently been 

shown to be complexes of species, each with a narrow host range (Burckhardt and 

Lauterer 2002). 

Many psyllids form galls on their host plant. These may include simple 

irregular distortions of the leaf or shoot, through leaf pit galls or roll leaf galls to 

complex enclosed gall structures on leaves, shoots, flowers rootlets and stems. 

Detailed information on gall formation and the morphological adaptations for 

living in different types of galls is reviewed by Hodkinson (1984) and Burckhardt 

(2005b). This study avoids detailed description of gall formation and focuses, 

where appropriate, on the adaptive significance of galls within individual psyllid 

life cycles. 

The paper initially considers the important constraints, adaptations and 

modifications of psyllid biology that have shaped their life cycles. It analyzes how 

these life cycle elements and adaptations have been assembled and combined to 

produce the wide range of life histories we observe among the world’s psyllid fauna 

today. The relative significance of phylogeny and environment are assessed as 

predictors of psyllid life histories. 

Important elements of psyllid life histories 

Development rate and voltinism 

Ambient temperature is a major determinant of egg and larval development rates in 

non-diapausing psyllids and, as such, governs the potential number of generations 

per annum (voltinism). The slowest development rate recorded is for Strophingia 

ericae on Calluna at high elevation, which, including two periods of winter diapause, 

takes 2 years to complete one generation, (Hodkinson 1973b). By contrast, 

multivoltine tropical/subtropical species such as Heteropsylla cubana, Diaphorina 

citri, Trioza erytreae and Trioza magnicauda, with free-running life cycles, may 

complete between 8 and 16 generations per annum (Table 1). Development rates and 

resultant generation times may, however, differ between seasons, depending on 

varying ambient temperatures as in Phytolyma fusca on Milicia, Ctenarytaina 

spatulata on Eucalyptus and Diaphorina citri on Citrus (Ledoux 1955; Bigornia and 

Obana 1974; Shahid and Khan 1976; Perez Otero et al. 2005). Many temperate 

species are univoltine, with a relatively short development period compressed within 

and synchronized with the early growing season of the host plant (Table 1). Arctic 

species, including many Cacopsylla, Psylla and Bactericera species, despite their 

adaptations to harsher climates, almost invariably show a similar trend to 

univoltinism (Table 1) (Hodkinson et al. 1979; Hodkinson and Bird in press). 

Among multivoltine temperate species such as Trioza urticae on Urtica, various 

Cacopsylla spp. on Pyrus and Agonoscena cisti on Pistacia the number of generations 

per annum rarely exceeds six, and is usually no more than than three to four (Onillon 

1969; An et al. 1996; Lauterer 1998; Souliotis and Tsourgianni 2000). Some widely 

distributed species, such as Trioza cinnamomi on Cinnamomum are univoltine in the 

cooler parts of their range but become multivoltine elsewhere (Miyatake 1969; 

Rajapakse and Kulasekera 1982). Strophingia ericae, cited previously, becomes unirather 

than semivoltine at lower warmer altitudes (Hodkinson 1973b).


Table 1. Life history characteristics of the world Psylloidea. The psyllid classification follows White and Hodkinson (1985) updated to include recent 

changes. Where subfamilies comprise of a single tribe the subfamily name is given. Note: abbreviations: climatic zone: TrM, tropical moist; TrD, tropical 

dry; TrS, tropical seasonal; M, Mediterranean; TeM, temperate moist; TeD, temperate dry; B, boreal; plant functional type of Raunkiær, based on 

overwintering strategy: P,Phanaerophyte (tall trees and shrubs, overwintering buds above soil surface); C, Chamaephyte (low growing or prostrate dwarf 

shrubs, overwintering buds ,25 cm above soil surface); H, Hemicryptophyte (overwintering bud at soil surface); G, Geophyte (overwintering bud below 

soil surface); He, Helophyte (marsh plants); T, Therophyte (overwintering as seed); Par, parasitic on other plants; d, deciduous; e, evergreen; s, 

semideciduous; overwintering stage: E, egg; L, larva; A, adult; overwintering site: on the host plant: T, trunk/stem; S, shoot; L, leaf; R, roots; B, buds; 

elsewhere: C, conifers/evergreen shrubs; LL, leaf litter; voltinism: M, multiple generations per year, number not fully determined, otherwise number of 

generations per annum stated; feeding site: S, shoot apex; L, expanded leaf; F, flower; St, stem; R, roots; B, buds; gall type: D, general distortion of leaf 

and/or shoot; P, pit gall on leaf; R, roll leaf gall; Ro, root gall; Lf, leaf-fold gall; F, flower gall; El, enclosed leaf gall; Es, enclosed stem gall; Eb, enclosed 

bud gall; lerp formation indicated by (X). 

Host plant(s) References 

Lerp former 

Gall 

Feeding site 

Voltinism 

Overwintering elsewhere 

Overwintering on host 

Overwintering stage 

Plant type 

Higher taxon Species Climate zone 


S Calluna Hodkinson (1973a, 

1973b), Parkinson and 

Whittaker (1975), 

Lauterer (1976), 

Whittaker (1985), Miles 

et al. (1997, 1998), 

Hodkinson et al. (1999), 

Butterfield et al. (2001) 

TeM Pe/C L S 1 or 

0.5 

Psyllidae 

Strophingiinae Strophingia ericae 

(Curtis) 

TeM/M Pe/C L S 1 S Erica Rapisarda (1990a), 

Hodkinson et al. (1999) 

S. cinereae 

Hodkinson

Table 1. (Continued.) 


Lerp former 

Gall 






Plant type 




Liviinae Livia crefeldensis TeM H A S 1 S D Carex Ossiannilsson (1992) 

Mink 

L. junci (Schrank) TeM H A S 1+ S D Juncus Verrier (1929), Heslop- 

Harrison (1949b), 

Schmidt (1966), 

Gegechkori (1984) 

L. maculipennis TeM H A C 1? S D Juncus McAtee (1915), Weiss and 

(Fitch) 

West (1922), Heslop- 

Harrison (1949b) 

L. mediterranea M/TeD H A C 1 S Juncus Gegechkori (1984) 

Loginova 

Aphalarinae 

Phytolymini Phytolyma fusca TrS Ps ELA S M S/L El Milicia Vosseler (1906), White 

Alibert 

(1966, 1967), Ledoux 

(1955) 

P. lata (Walker) TrS Ps ELA S M S/L El Milicia White (1966, 1967), 

Cobbinah (1986) 

Gyropsyllini Gyropsylla ilicis TrS Pe A S 1 L R Ilex Mead (1983) 

(Ashmead) 

G. spegazziniana TeM Pe E S 1 L R Ilex Brèthes (1921), Leite and 

(Lizer) 

Zanol (2001)




Lerp former 

Gall 






Plant type 



Aphalarini Aphalara affinis TeM H A C 1? L Stellaria Ossiannilsson (1992) 

(Zetterstedt) 

A. avicularis TeM H A C/L 2+ L P Polygonum Lauterer (1991), 

Ossiannilsson 

Ossiannilsson (1992) 

A. borealis Heslop- TeM H A C 1 Polygonum Lauterer (1979), Conci 

Harrison 

et al. (1993) 

A. calthae (L.) TeM He A C 1 S/L/F Caltha Ossiannilsson (1992) 

A. crispicola TeM H A C ? L P Rumex Lauterer (1982) 

Ossiannilsson 

A. exilis (Weber TeM H A C/L 1 S Rumex Lauterer (1976), 

and Mohr) 

Gegechkori (1984), 


A. freji Burckhardt TeM H A C 1–2 S Polygonum Gegechkori (1984), 

and Lauterer 


Ossiannilsson (1992), 

Conci et al. (1993) (all 

as A. polygoni), 

Burckhardt and 

Lauterer (1997) 

A. longicaudata TeM H A C/L 1 S Polygonum Lauterer (1976) 

Schaefer



Lerp former 

Gall 






Plant type 


TeM H A C 1 L Polygonum Gegechkori (1984), Conci 

et al. (1993) 

TeD H A ? 1 ? Rumex Gegechkori (1984) 

Aphalarini A. maculipennis 

Löw 

A. nigrimaculosa 

Gegechkori 

A. polygoni 

Foerster 


TeM H A C 2 L Rumex Lauterer (1982), 



(all as A. rumicicola) 



TeM H L R? 1 S Achillea Conci et al. (1993) 


TeM H L S 1 S Senecio Lauterer and Burckhardt 

(2004) 

Craspedolepta 

bulgarica 

(Klimaszewski) 

C. campestris 

Lauterer and 

Burckhardt 

C. conspersa (Löw) TeM H L R? 1 S Artemisia Conci et al. (1993) 

C. crispata Lauterer TeM H L S 1 S Senecio Lauterer and Burckhardt 

and Burckhardt 

(2004) 

C. eas (McAtee) TeD H L S 1 St Phlox Wheeler (1994) 

C. flavipennis TeM H L S 1 S Leontodon Lauterer and Burckhardt 

(Foerster) 

(2004)




Lerp former 

Gall 






Plant type 


TeM H L R? 1 S Artemisia Conci et al. (1993), 

Hodkinson 

(unpublished) 

TeM/B H L R 1 S Chamerion Lal (1934), Sampo (1975), 

Lauterer (1993a), Bird 

and Hodkinson (1999, 

2005), Hodkinson and 

Bird (2006b) 

TeM H L R 1 L Achillea Lauterer (1991), 


(unpublished) 

Aphalarini C. malachitica 

(Dahlbom) 

C. nebulosa 

(Zetterstedt) 


C. nervosa 

(Foerster) 

C. omissa Wagner TeM H L R 1? S Artemisia Lauterer (1991) 

C. sonchi (Foerster) TeM H L S 1? S Leontodon Lauterer and Burckhardt 

(2004) 

C. schwarzi B H L R? 1 S Chamerion Hodkinson and Bird 

(Ashmead) 

(1998, unpublished) 

C subpunctata TeM H L R 1 R/S Ro Chamerion Lauterer and Baudys 

(Foerster) 

(1968), Bird and 

Hodkinson (1999, 

2005), Hodkinson and 

Bird (2006b)



Lerp former 

Gall 






Plant type 


Aphalarini C. veaziei (Patch) TeM/TeD H L S 1 S Solidago Journet (1984), 


(unpublished) 

M Th EL S 1 S Salicornia, Conci et al. (1993) 

Suaeda 

Salsola, 

Petrosimonia 

M Pe EL S 1 S Suaeda Conci et al. (1993) 

Rhodochlanis 

bicolor (Scott) 


R. salsolae 

(Lethierry) 

Rhinocolinae 

Rhinocolini Agonoscena 

cisti (Puton) 


M Pe A L 5–6 L Pistacia Lauterer et al. (1998), 

Souliotis and 

Tsourgianni (2000) 

TeD Pe A T 2–5 L Pistacia Tokmakoglu (1973), 

Mohammed and Sheet 

(1989) (as targionii), 

Souliotis and 

Tsourgianni (2000), 

Mehrnejad (2002), 

Mehrnejad and 

Copland (2005, 2006a, 

2006b) 

M Pe L L 3 L Ruta Heeger (1856), Douglas 

(1878), Boselli (1930), 

Ramirez Gomez (1960) 

A. pistaceae 

Burckhardt 

and Lauterer 

A. succincta (De 

Geer)




Lerp former 

Gall 






Plant type 


M Pe A S M S Pistacia Davatchi (1958), Conci 

et al. (1993) 

TeM Pd E S 1 S Acer Löw (1880), Gegechkori 

(1984), Lauterer (1991), 

Rapisarda and Belcari 

(1999) 

M Pd EN S 1 S Acer Conci et al. (1993) 

Rhinocolini A. targionii 

Lichtenstein 

Rhinocola aceris 

(Foerster) 


TeD Pe L S 1 S Calligonum Loginova (1970, 1976) 

R. fusca 

Burckhardt 

Acaerus calligoni 

(Baeva) 

A. deminutus 

(Loginova) 

A. luridus 


A. memoratus 


A. tumidulus 


A. turkistanika 

(Löw) 

Pachypsylloides 

aemulus 


Pachypsylloidini 






TeD Pe L S .1 S Es Calligonum Loginova (1970)



Lerp former 

Gall 






Plant type 


TeD Pe L S .1 S Es Calligonum Loginova (1970) 





Pachypsy- P. argutus 

lloidini Loginova 

P. errator 


P. patulus 


P. pompatus 


P. reverendus 


Paurocephalinae Camarotoscena 

speciosa (Flor) 



M/TeD Pd A C 2? L R Populus Loginova and Parfentiev 

(1958), Gegechkori 

(1984), Lauterer 

(1993b), Conci et al. 

(1993) 

TrM Pe ELA L C S/L T Morus Hsieh and Chen (1977) 

Paurocephala 

psylloptera 

Crawford 

P. russellae Mathur TrM Pe L L 7 L P Kydia Mathur (1935, 1975) 

Togepsyllinae Togepsylla TeM Pe A C 1 L P Lindera Miyatake (1970) 

matsumurana 

Kuwayama




Lerp former 

Gall 






Plant type 


TrM Ps ELA S C S Triplochiton Kudler (1968), Osisanya 

(1974a, 1974b) 

TrM Ps ELA S C S Triplochiton Osisanya (1974a, 1974b) 


TrM Pe ELA S C S Miconia Brown and Hodkinson 


TrM Pe ELA S C S Miconia Burckhardt et al. (2005) 

TrM Pe ELA L C L Luehea Brown and Hodkinson 


TrM Pe ELA S C S Conostegia Conconi (1973) 

TrM Pe ELA C L Ricinodendron Aléné et al. (2005a, 2005b) 

Euphyllurinae 

Diclidophlebiini Diclidophlebia 

eastopi 

Vondracek 

D. harrisoni 

Ossisanya 

D. longitarsata 

(Brown and 

Hodkinson) 

D. lucens 

(Burckhardt 

et al.) 

D. nebulosa 

(Brown and 

Hodkinson) 

D. tuxtlaensis 

(Conconi) 

D. xuani 

Messi et al.



Lerp former 

Gall 






Plant type 


M Pe A S 3+ S Olea Silvestri (1934), Ramirez 

Gomez (1958), 

Rapisarda (1990a), 

Conci et al. (1993), Del 

Bene et al. (1997), 

Arambourg and 

Chermiti (1986), 

Tzanakakis (2003, 

2006) 

TrD Pe A S 1+ S Olea Thakur et al. (1989) 

Euphyllurini Euphyllura 

olivina (Costa) 



M Pe A S 1 S Olea, Phillyrea, 

Osmanthus 

E. pakistanica 


E. phillyreae 

Foerster 

Loureiro Ferreira (1946), 

Ramirez Gomez (1958), 

Prophetou and 

Tzanakis (1977,1986), 

Stavraki (1980), 

Lauterer et al. (1986), 

Rapisarda (1991), 

Conci et al. (1993), 

Prophetou (1993,1997), 

Del Bene et al. (1997), 

Tzanakakis (2003, 

2006)




Lerp former 

Gall 






Plant type 


M Pe A S 2–3 S Olea Mustafa (1984, 1989a, 

1989b), Mustafa and 

Najar (1985) 

TeM Ps A C/L 1 S Ligustrum Konovalova (1976) 

Euphyllurini E. straminea 



TeM/M Pe EL S ? S/St X Arbutus Ferris and Hyatt (1923) 

Pe ELA S up 

to 8 

TrS/M/ 

TeM 

Ligustrinia 

herculeana 


Neophyllura arbuti 

(Schwarz) 

Ctenarytainini Ctenarytaina 

eucalypti (Ferris 

and Klyver) 

S Eucalyptus Fox Wilson (1924), 

Azevedo and Figo 

(1979), Bertaux et al. 

(1996), Malausa and 

Giradet (1997), 

Rapisarda (1998), 

Hodkinson (1999), 

Olivares (2000), Purvis 

et al. (2002) 

TrS/TeM Pe ELA S M S Eucalyptus Hodkinson (2007 and 

unpublished) 

C. peregrina 

Hodkinson



Lerp former 

Gall 






Plant type 


TrS/M Pe ELA S M S Eucalyptus Mansilla et al. (2004), 

Costanzi et al. (2003), 

Perez Otero et al. (2005) 

TeM Pe ELA S 3 S Boronia Mensah and Madden 

(1992a, 1992b, 1993a, 

1993b, 1994) 

Ctenarytainini C. spatulata 

Taylor 


C. thysanura 

(Ferris and 

Klyver) 

Diaphorininae 

Diaphorinini Diaphorina citri 

Kuwayama 


TrS Pe ELA S 8–16 S Citrus Hussain and Nath (1927), 

Atwal (1962), Mangat 

(1966), Catling (1970), 

Atwal et al. (1970), 

Pande (1971), Bigornia 

and Obana (1974), 

Shahid and Khan 

(1976), Mead (1977), 

Lakra et al. (1983), Tsai 

and Liu (2000), Liu and 

Tsai (2000), Nakata 

(2006)




Lerp former 

Gall 






Plant type 



Diaphorinini D. communis TrS Pe A L 9 S Murraya Beeson (1941), Mathur 

Mathur 

(1975) 

D. lycii Loginova M/TeD Pe ELA S 5 Lycium Boselli (1960) (as putoni), 

Rapisarda (1990a) 

Psyllopseini Psyllopsis TeM Pd E S 1–2 L R Fraxinus Lal (1934), Gegechkori 

discrepans (Flor) 

(1984) 

P. distinguenda TeM Pd E S 2 L R Fraxinus Lauterer (1982), Conci 

Edwards 

and Tamanini (1990) 

P. fraxini (L.) TeM Pd E S 1–2 L R Fraxinus Heslop-Harrison (1942), 

Loginova (1954), 

Nguyen (1970b), Conci 


P. fraxinicola TeM Pd E S 1–2 L Fraxinus Lal (1934), Loginva 

(Foerster) 

(1954), Ramirez Gomez 

(1956), Conci and 

Tamanini (1990) 

P. machinosus M/TeD Pd E S 2 L ? Fraxinus Loginova (1968), Conci 



P. meliphila (Löw) M/TeD Pd E S ? L Fraxinus Rapisarda (1998) 

P. narzykulovi TeD Pd E S 2 L Fraxinus Conci and Tamanini 

Baeva 

(1990)



Lerp former 

Gall 






Plant type 



TeD Pd E S 2 L L Fraxinus Conci and Tamanini 

(1990) 

TeD Pd E S 2 L L Fraxinus Conci and Tamanini 

(1990) 

TrS Pe ELA L ? L El Baccharis Espirito-Santo and 

Wilson Fernandez 

(1998, 2002) 

TrD/M Ps ELA S M S Acacia Conci et al. (1993), 

Rapisarda 

(1985,1993a), 

Rapisarda and Belcari 

(1999) 

Ps ELA S M S Acacia Palmer and Witt (2006) 

Psyllopseini P. repens 


P. securicola 


Aphalaroidinae Baccharopelma 

baccharidis 

(Burckhardt) 

Acizziinae Acizzia 

acaciaebaileyanae 

(Froggatt) 


A. melanocephala 


TrD Ps ELA S M S Acacia Hoffman et al. (1975), 

Webb (1977), Webb 

and Moran (1978) 

Mifsud 

A. russellae Webb 

and Moran




Lerp former 

Gall 






Plant type 


Heslop-Harrison (1949a) 

(as Neopsyllia indica), 

Munro (1965), Koehler 

et al. (1966), 

Madubunyi (1967), 

Madubunyi and 

Koehler (1974), Leeper 

and Beardsley (1976), 

Arzone and Vidano 

(1985), Rapisarda 

(1993a), Rapisarda and 

TrD/M Ps ELA S M S Acacia, 

Albizzia 

Acizziinae A. uncatoides 

(Ferris and 

Klyver) 


Belcari (1999) 

TeD Pd A S 1 S Morus Chon (1964), Kuwayama 

(1971), Waku and Endo 

(1987), Arai (1991, 

1993) 

Anomoneurinae Anomoneura mori 

Schwarz



Lerp former 

Gall 






Plant type 


S Leucaena Moxon (1984), Chazeau 

(1987), Oka and 

Bahgiawati (1988), 

Singh (1988), Yasuda 

and Tsurumachi (1988), 

Takara et al. (1990), 

Rauf et al. (1990), Patil 

et al. (1994), Austin 

et al. (1996), Ogol and 

Spence (1997), Geiger 

and Gutierrez (2000) 

TrD Ps ELA S M (8– 

10) 

Ciriacreminae Heteropsylla 

cubana 

Crawford 



TrS Ps ELA S ,8 S Mimosa Willson and Garcia (1992) 

TrS Ps ELA S C S Prosopis Donnelly (2002) 

TeM/M Pe A S 2 S Cytisus Watmough (1968a, 1968b) 

H. spinulosa 

Muddiman et al. 

H. texana 

Crawford 

Arytaininae Arytaina genistae 

(Latreille) 

A. africana 

Heslop-Harrison 

M Pe E S 2 S Adenocarpus Rapisarda (1988) (as 

maculata), Rapisarda 

(1990a), Conci et al. 

(1993)




Lerp former 

Gall 






Plant type 


M Pe E S 1 S Genista Rapisarda (1989c), Conci 

et al. (1993) 

Arytaininae Arytainilla 

barbagalloi 

Rapisarda 


A. cytisi (Puton) M Pe E ST 1 S Genista Rapisarda (1988, 1990a, 

Calicotome 1990b), Conci et al. 

(1993) 

A. spartiicola M Pe E S 1 S Cytisus Conci and Tamanini 

(Sˇulc) 


(1993) 

A. spartiophila M Pe E S 1 S Cytisus Heslop-Harrison (1951), 

(Foerster) 

Watmough (1968a, 

1968b) 

Cyamophila TeD C A ? 1 S Astragalus Gegechkori (1984) 

astragalicola 

Gegechkori 

C. caraganae TeD H A ? 1 S Caragana Gegechkori (1984) 


C. caucasica TeD H A ? 1 S Glycyrrhiza Gegechkori (1984) 

(Baeva) 

C. coluteae Baeva TeD C A ? 2 S Colutea Gegechkori (1984) 

C. dicora Loginova TeD C A S 1 S Astragalus Naeem and Behdad (1988) 

C. glycyrrhizae TeD/M H/C A ? 2–3 S Glycyrrhiza Gegechkori (1984) 

(Becker)



Lerp former 

Gall 






Plant type 


TeD/M H A ? 2 S Medicago Gegechkori (1984) 

TeD H/C A ? 1 S Hedysarum Gegechkori (1984) 

TeM H A C 1 S Anthyllis Conci and Tamanini 

(1986a, 1989b), Conci 

et al. (1993) 

M Pe EL S 1 S Genista Conci et al. (1993) 

Arytaininae C. medicaginis 

(Andrianova) 

C. megrelica 

(Gegechkori) 

C. prohaskai 

(Priesner) 


Livilla bimaculata 

Hodkinson and 

Hollis 


L. cognata (Löw) TeM Pe E/L? S 1 S Chamaecytisu, Conci et al. (1993) 

Lemboptropis 

L. horvathi (Scott) M Pe EL S 1 S Genista Conci et al. (1993) 

L. magna M Pe L S 2 S Genista Rapisarda (1988, 1990b), 


Conci et al. (1993) 

and Hollis 

L. pyrenaea TeM Pe AE S 1 S Genista Conci et al. (1993) 

(Mink) 

L. retamae M Pe E/L S 1 S Retama Rapisarda (1991, 1992), 

(Puton) 


L. spectabilis TeM/M Pe A/E S 1 S Spartium Rapisarda (1988, 1992), 

(Flor) 

Conci et al. (1993)




Lerp former 

Gall 






Plant type 



Arytaininae L. variegata TeM/M Pe E/L? S 1 S Laburnum Conci et al. (1993) 

(Löw) 

L. vicina (Löw) TeM/M Pe A S 1 S Cytisus Conci and Tamanini 

(1988), Conci et al. 

(1993) 

L. vittipennella TeM/M Pe L S 1 S Genista Conci et al. (1993) 

(Reuter) 

Psyllinae Psylla alni (L.) TeM Pd E S 1 S Alnus Lal (1934), Lauterer 


(1984), Ossiannilsson 

(1992) 

P. alpina Foerster TeM Pd E S 1 S Alnus Conci et al. (1993) 

P. betulae (L.) TeM Pd E S 1 S Betula Gegechkori and 

Djibladzne (1976), 



P. betulaenanae B Pd E S 1 S Betula Ossiannilsson (1992), 

Ossianilsson 

Hodkinson and Bird (In 

press)



Lerp former 

Gall 






Plant type 




Psyllinae P. borealis B Pd E S 1 S Alnus Hodkinson and Bird (In 

(Horvath) 

press) 

P. cordata M Pd E S 1 S Alnus Chiara et al. (1990), Conci 

Tamanini 

et al. (1993), Rapisarda 

and Belcari (1999) 

P. floccosa Patch TeM Pd E S 1 S Alnus Patch (1909) 

P. fusca 

TeM Pd E S 1 S Alnus Lauterer (1998), 

(Zetterstedt) 



P. negundinis TeM Pd E S 1 S Acer Mally (1894) 

Mally 

P. trimaculata TeM Pd E S 1 S Prunus Osborn (1922) 

Crawford 

Baeopelma M Pd E S 1 S Ostrya Rapisarda (1990b), Conci 

colorata (Löw) 

et al. (1993) 

B. foersteri (Flor) TeM Pd E S 1 S Alnus Lal (1934), Lauterer 




(1993)




Lerp former 

Gall 






Plant type 


TeM/M Pe EL S 1 L D Buxus Lal (1934), Wilcke (1941), 

Nguyen 

(1965,1968,1969), 

Sampo (1975), 

Psyllinae Asphagidella buxi 

(L.) 


Malenovsky (1999) 

Spanioneura TeM/TeD Pe EA? S 1 or L Buxus Ramirez Gomez (1956), 

fonscolombei 

M? 


(Foerster) 

(literature disagrees) 

S. caucasica TeD Pe E S 1 ? Buxus Gegechkori and 


Djibladzne (1976) 

Cacopsylla sensu stricto 

Cacopsylla mali TeM Pd E S 1 S Malus Brittain (1922a, 1922b, 

(Schmidberger) 

1923a, 1923b), Speyer 

(1929), Przybylski 

(1970), Jonsson (1983), 



C. peregrina TeM Pd E S 1 S Crataegus Missonnier (1956), Sutton 

(Foerster) 

(1983, 1984), 


C. sorbi (L.) TeM Pd E S 1 S Sorbus Conci et al. (1993)



Lerp former 

Gall 






Plant type 



Psyllinae C. ulmi (Foerster) TeM Pd E S 1 S Ulmus Gegechkori (1984), 




Cacopsylla (Hepatopsylla) on Salix 

C. ambigua TeM Pd E S 1–2 S Salix Lal (1934), Lauterer 

(Foerster) 

(1976, 1999) 

C. brunneipennis TeM/B Pd A L 1 F/S Salix Gegechkori (1984), Hill 

(Edwards) 

and Hodkinson (1995), 

Lauterer (1999), Hill 

et al. (1998) 

C. compar TeD Pd A ? 1 ? Salix Gegechkori (1984) 


C. elegantula B Pd A C 1 F/S Salix Ossiannilsson (1992), 

(Zetterstedt) 


C. fraterna TeD Pd A C 1 ? Salix Gegechkori (1984) 


B P/Cd A L 1 F/S Salix Hodkinson (1997), 

Hodkinson and Bird (In 

press) 

TeM Pd E S 1 S Salix Lauterer (1999) 

(Gegechkori) 

C. groenlandica 

(Sˇulc) 

C. intermedia 

(Löw)




Lerp former 

Gall 






Plant type 


Psyllinae C. iteophila (Löw) TeM Pd A C 1 F/S Salix Conci and Tamanini 


(1993) 

C. macleani B Pd A L 1 F/S Salix Hodkinson et al. (1979) 

(Hodkinson) 

C. memor TeD Pd A ? 1 ? Salix Gegechkori (1984) 

TeM Cd A L 1 F/S Salix Gegechkori (1984), 

Lauterer (1993c, 1999), 


Hill and Hodkinson 

(1996) 

B Pd A C 1 F/S Salix Gegechkori (1984), 




C. moscovita 

(Andrianova) 


C. nigrita 

(Zetterstedt) 

C. palmeni (Löw) B Pd/Cd A L 1 F/S Salix Hodkinson et al. (1979), 


Hill and Hodkinson 

(1995), Hill et al. (1998) 

C. parvipennis TeM Pd/Cd A L 1 F/S Salix Ossiannilsson (1992) 

(Löw) 

C. phlebophyllae B C A L 1 F/S Salix Hodkinson et al. (1979) 


C. propinqua B Pd A L 1 F/S Salix Ossiannilsson (1992), Hill 

(Schaefer) 

and Hodkinson (1995), 

Hill et al. (1998)



Lerp former 

Gall 






Plant type 


TeM Pd A C 1 F/S Salix Lauterer (1999), 



TeM Pd A C/L 1 F/S Salix Gegechkori (1984), Conci 

et al. (1993) 

Psyllinae C. pulchra 

(Zetterstedt) 



C. saliceti 

(Foerster) 

C. zaecevi (Sˇulc) B Pd/Cd A L 1 F/S Salix Hodkinson et al. (1979), 


Other Cacopsylla (Hepatopsylla) 

C. bidens (Sˇulc) TeM Pd A T 4–7 S Pyrus Lauterer (1979), 

Gegechkori (1984) (as 

C. vasiljevi) 

C. corcontum TeM Pd A C 1 S Sorbus Lauterer (1976, 1999), 

(Sˇulc) 

Ossiannilson (1992) 

C. hippophaes TeM/TeD Pd E T 1 S Hippophae Lauterer (1982, 1993a, 

(Foerster) 

1999), Gegechkori 


(1993) 

C. ledi (Flor) B Pd A ? 1 S Ledum Ossiannilsson (1992) 

C. notata (Flor) M Pd A T M S Pyrus Conci et al. (1993) 

C. myrtilli B Cd E S 1 S Vaccinium Lauterer (1999), 

(Wagner) 

Ossiannilsson (1992)




Lerp former 

Gall 






Plant type 



Psyllinae C. pyri (L.) TeM Pd A T 2–8 S Pyrus Wille (1950), 

Bonnemaison and 

Missonnier (1955a, 

1955b, 1956), Nguyen 

(1964, 1967a, 1967b 

1970a, 1971, 1972a, 

1972b, 1973, 1975), 

Wojnarowska 

et al. (1960), Nucifora 

(1969), Lazarev (1979), 

Deronzier (1981, 1984), 

Deronzier and Atger 

(1980), Atger (1982), 


Rieux and d’Arcier 

(1990), Lyoussoufi et al. 

(1988, 1992, 1994), 

Stratopoulou and 

Kapatos (1995a, 

1995b), Souliotis and 

Broumas (1998), 

Kapatos and 

Stratopoulou (1996, 

1999), Schaub et al. 

(2005)



Lerp former 

Gall 






Plant type 


TeM Pd A T 3–5 S Pyrus Slingerland (1892), Ross 

(1919), Schaefer (1949), 

Siddiqui (1949), Wilde 

(1962, 1965), Wilde and 

Watson (1963), Wong 

and Masden (1967), 

Rasmy and MacPhee 

(1970), Burts (1970), 

Oldfield (1970), Radjabi 

and Behechti (1975), 

McMullen and Jong 

(1972, 1976, 1977), Fye 

(1983), Mustafa and 

Hodgson (1984), 

Savinelli and Tetrault 

(1984), Krysan (1990), 

Krysan and Higbee 

(1990), Horton et al. 

(1990a, 1990b), Horton, 

Higbee, et al. (1994), 

Horton et al. (1998), An 

et al. (1996) 

Psyllinae C. pyricola 

(Foerster) 


Journal of Natural History 93




Lerp former 

Gall 






Plant type 



Psyllinae C. rhododendri TeM Pd E S 1 S Rhododendron Conci et al. (1993) 

(Puton) 

C. viburni (Löw) TeM Pd E S 1 S Viburnum Gegechkori and 




C. visci (Curtis) TeM Par on E S 2–3 S Viscum, Bin (1970), Lauterer 

Pd 

Loranthus (1999), Hansen and 

Hodkinson (2006) 

C. zetterstedti TeM/TeD Pd E T 1 S Hippophae Lauterer (1982, 1993a, 

(Thomson) 

1999), Ossiannilsson 


(1993) 

Cacopsylla (Thamnopsylla) 

C. affinis (Löw) TeM Pd A C 1 S Crataegus Lauterer (1982, 1999), 

Sutton (1984) (as 

subferruginea) 

C. alaterni M Pe ELA S up to S Rhamnus Rapisarda (1989a, 1990a), 

(Foerster) 

5 


C. albipes (Flor) TeM Pd A C 1 ? Sorbus Gegechkori (1984), Conci 

et al. (1993)



Lerp former 

Gall 






Plant type 


TeM Pd A ? 1–2 S Sorbus Gegechkori (1984), 

Lauterer (1993c, 1999), 


TeD Pd A ? 1 ? Gegechkori (1984) 

Psyllinae C. breviantennata 

(Flor) 



C. cotoneasteris 


C. crataegi TeM Pd A C 1 S Crataegus Ramirez Gomez (1956), 

(Schrank) 

Nguyen (1963), 




C. euxina M Pd ELA S M S Rhamnus Rapisarda (1989a) 


C. fasciata TeD Pd A C 2 S Spiraea Gegechkori (1984) 

(Horvath) 

C. incerta (Baeva) TeD Pd A C 1 S Rhamnus Gegechkori (1984) 

C. limbata TeM Pd A C 1 S Rhamnus Conci and Tamanini 

(Meyer-Dur) 

(1982, 1988), Conci 

et al. (1993)




Lerp former 

Gall 






Plant type 


Lal (1934), Domenichini 

(1967), Lazarev (1972), 

Sutton (1983), 


Lauterer (1999), Conci 

et al. (1993), Tedeschi 

TeM Pd A C 1 S Crataegus, 

Malus 

Psyllinae C. melanoneura 

(Foerster) 


et al. (2002) 

S Myrthus Conci et al. (1993) 

C. myrthi (Puton) M Pe ELA S up to 

5 

C. picta (Foerster) TeM Pd A C 1 S Malus Harisanov (1966b) (as 

costalis), Lauterer 

(1999) 

C. pruni (Scopoli) TeM Pd A C 1 S Prunus Harisanov (1966a), 




et al. (1993), Labonne 

and Lichou (2004) 

C. pulchella (Löw) M Pd A C 1 S Cercis Burckhardt (1999), Conci 

et al. (1993), Rapisarda 

and Belcari (1999)



Lerp former 

Gall 






Plant type 


TeM/M Pd A C 1 S Pyrus Brocher (1926), 

Wojnarowska (1962), 

Lazarev (1975), 



TeM Pd A C 1 S Rhamnus Gegechkori (1984), 



TeD Pd A C 1 ? Ribes Gegechkori (1984) 

Psyllinae C. pyrisuga 

(Foerster) 

C. rhamnicola 

(Foerster) 



C. steinbergi 


Cacopsylla (Chamaepsylla) 

C. hartigii (Flor) TW Pd E S 1 S Betula Gegechkori (1984), 



(unpublished) 

Other Miscellaneous ‘Psylla’ spp. 

Psylla diospyri TrS Pd E S 2 L R Diospyros Ashmead (1881) 

Ashmead 

Psylla isitis TrS Pe ELA S C S Indigofera Grove and Ghosh (1914), 

Buckton 

Maxwell-Lefroy (1913), 

Mathur (1975) 

Psylla nr. simlae TrS Ps ELA S M up S Bauhenia Mathur (1935, 1975) 

Crawford 

to 11




Lerp former 

Gall 






Plant type 


Spondyliaspididae 

Euphalerinae Euphalerus hiuri TeM Pd E T 1 L Lf Caesalpinia Miyatake (1973) 

Miyatake 

E. nidifex Schwarz TrS Pe ELA L M L X Piscidia Mead (1967), Russell 

(1971) 

E. ostreoides TrS Pe ELA L M L El Lonchocarpus Ferreira et al. (1990) 

Crawford 

E. vittatus TrS Pe E S 5 S Cassia Beeson (1941), Mathur 


Crawford 

(1935) 

Pachypsyllinae Celtisapsis japonica TeM Pd E S 2 S X Celtis Miyatake (1968b, 1980, 

(Miyatake) 

1994) 

C. usabai Miyatake TeM Pd E S 1 S X Celtis Miyatake (1980, 1994) 

Pachypsylla TeM Pd L B 1 B/L B/El Celtis Riley (1890), Weiss 

celtidisgemma 

(1921), Walton (1960) 

Riley 

P. celtidisinternis TeM Pd A ? 1 B B Celtis Weiss (1921), Walton 

Mally 

(1944), Smith and 

Taylor (1953) 

P. celtidismamma TeM Pd A T 1 L El Celtis Riley (1890), Smith and 

(Fletcher) 

Taylor (1953), Heard 

and Buchanan (1998)



Lerp former 

Gall 






Plant type 




Pachypsyllinae P. celtidisvesicula TeM Pd A T 1 L El Celtis Riley (1890), Smith and 

Riley 

Taylor (1953) 

P. venusta TeM Pd L L 1 L El Celtis Riley (1890), Smith and 

(Osten-Sacken) 

Taylor (1953) 

Tetragonocephala TeM Pd A T 1 L X Celtis Riemann (1958) 

flava Crawford 

Spondyliaspidinae Boreioglycaspis TrS Pe ELA L C L Melaleuca Purcell et al. (1997), 

melaleucae Moore 

Wineriter et al. (2003) 

Cardiaspina TrS Pe ELA L 2–3 L X Eucalyptus Clark (1962, 1963a, 

albitextura Taylor 

1963b), Clark and 

Dallwitz (1975), 

Morgan (1984), Collett 

(2001) 

C. densitexta TrS Pe ELA L 3 L X Eucalyptus White (1968, 1970b, 

Taylor 

1970c, 1973), Morgan 

(1984), Collett (2001) 

C. fiscella Taylor TrS Pe ELA L 5 L X Eucalyptus Campbell (1992) 

C. maniformis TrS Pe ELA L 4 L X Eucalyptus Campbell (1992) 

Taylor 

Creiis costatus TrS Pe ELA L 2+ L X Eucalyptus Clark and Dallwitz (1975) 

Froggatt




Lerp former 

Gall 






Plant type 



Spondyliaspidinae Glycaspis baileyi TrS Pe ELA L 2+ L X Eucalyptus Moore (1961) 

Moore 

G. brimlecombei TrS Pe ELA L 2+ L X Eucalyptus Clark and Dallwitz 

Moore 

(1975), Morgan (1984), 

Brennan, Hrusa et al. 

(2001), Brennan and 

Weinbaum (2001a, 

2001b, 2001c, 2001d) 

G. fuscovena TrS Pe ELA L M L X Eucalyptus Morgan (1984) 

Moore 

G. prepta Moore TrS Pe ELA L M L X Eucalyptus Clark and Dallwitz (1975) 

Spondyliapspis TrS Pe ELA L M L X Eucalyptus Solomon (1936) 

occidentalis 

Solomon 

Calophyidae 

Apsyllinae Apsylla cistellata TrM Pe L S 1 S Es Mangifera Mathur (1935, 1946), 

(Buckton) 

Mani (1948), Singh M 

(1959), Singh S (1954, 

1960), Prasad (1957), 

Chaterjee and Sebastian 

(1965), Singh and Misra 

(1978), Monobrullah 

et al. (1998)



Lerp former 

Gall 






Plant type 




Mastigimatinae Mastigimas ernstii TrM Pe ELA L M L R Cedrela Pintera (1982) 

(Schwarz) 

Mastigimas TrM Pe ELA L M L R Cedrela Pintera (1982) 

schwarzi 

(Tuthill) 

Calophyinae Calophya nigra TeM Pd A C 1 S Phellodendron Konovalova (1963), 

Kuwayama 

Miyatake (1992) 

C. nigrilineata TrS Pe ELA L M L P Tetragastris Iglesias (1983), Brown and 

Brown and 

Hodkinson (1988, 


unpublished) 

C. rhois (Löw) M/TeD Pd E or S 1 L P/R Cotinus Gegechkori (1984), Conci 

A 

et al. (1996) 

C. nigripennis TeM Pd L T 1 L Rhus Weiss and Nicolay (1918) 

Riley 

C. schini Tuthill TrS/M Pe ELA L M L P Schinus Downer et al. (1988) 

C. shinjii Sasaki TeM Pe A S 1 L Picrasma Miyatake (1992) 

C. triozomima TeM Pe L S 2 L D Rhus Wheeler and Rawlins 

Schwarz 

(1993) 

Phacopteronidae 

Phacopteron TrS Pe L L 3 L El Garuga Mathur (1935, 1946), 

lentiginosum 

Raman (1987) 

(Buckton)




Lerp former 

Gall 






Plant type 


M Pd E S 1 L Ficus Boselli (1929a), Ramirez 

Gomez (1956), 

Gegechkori (1984) (and 

as viridis), Rapisarda 

(1989b) (as viridis), 

Conci et al. (1996b), 

Tuncer (2002), Gencer 

et al. (2007) 

TrM Pe ELA S M S Antiaris Akanbi (1980) 

Homotomidae 

Homotominae Homotoma ficus 

(L.) 


TeM Pd E L 1–2 L Firmiana Ding et al. (1987) 

Triozaminae Triozamia lamborni 

(Newstead) 

Carsidaridae 

Carsidarinae Carsidara limbata 

(Enderlein) 

Mesohomotoma 

tessmannii 

(Aulmann) 

TrM Pe ELA S M S/F Theobroma Entwistle (1972), 

Kaufmann (1973), 

Igboekwe (1983), 

Igboekwe and Adenuga 

(1983), Messi (1983a, 

1983b) 

TrM Pe ELA S M S Durio Gadug and Hussein 

(1987) 

Allocarsidara 

malayensis 

(Crawford)



Lerp former 

Gall 






Plant type 


TeM Hel A C 2 L Comarum Lauterer (1982) 

Triozidae 

Triozini Bactericera 

acutipennis 

(Zetterstedt) 

B. albiventris 

(Foerster) 


TeM Pd A C 2 L Salix Gegechkori (1984), 




B Pd A L 1 L Salix Hodkinson et al. (1979) 


B. atkasookensis 


B brassicae TeM H A ? 1 ? Brassica Gegechkori (1984) 

(Vasil’ev) 

B. bohemica (Sˇulc) TeM H A C 1? L Geum Gegechkori (1984), 



B. bucegica TeM H A C 1 L Ranunculus Conci and Tamanini 

(Dobreanu and 


Manolache) 

(1996)




Lerp former 

Gall 






Plant type 


Triozini B. cockerelli (Sˇulc) TeD C ELA L L/C 3+ L P/D Solanaceae Compere (1916), Essig 

(1917), Lehrman (1930), 

Knowlton and Janes 

(1931), Knowlton 

(1933, 1934), Knowlton 

and Thomas (1934), 

Davis (1937), Janes and 

Davis (1937), List 

(1939a, 1939b) Swenk 

and Tate (1940), Pletsch 

(1947), Wallis (1946, 

1955), Liu and Trumble 

(2004, 2005, 2006, 

2007), Liu et al. (2006) 

B. crithmi (Löw) M/TeM H ELA L 2+ L Crithmum, Conci et al. (1996), 


Ferula Mifsud (1997) 

TeM Pd A C 1? L Salix Gegechkori (1984), 



TeM H A C 1–2 L Alchemilla Bin (1972), Gegechkori 



(1996) 

B. curvatinervis 

(Foerster) 

B. femoralis 

(Foerster)



Lerp former 

Gall 






Plant type 




Triozini B. harrisoni TeM H A C 1 L Geum Conci et al. (1996) 

(Wagner) 

B. kratochvili TeM G LA S 2–3 S Allium Lauterer (1965), Conci 

Vondracek 

and Tamanini (1991), 


B. modesta TeM H A L 1–3? L Sanguisorba, Lauterer (1991), Conci 

(Foerster) 

Poterium et al. (1996) 

B. nigricornis TeM H A C 2 L D Solanum Heinz and Profft (1939), 

(Foerster) 


Biase (1983), 



et al. (1996) 

B. perrissii Puton TeM H A L/C 1 S Artemisia Lauterer (1982) 

B. reuteri (Sˇulc) TeM H A ? ? 2? L Potentilla Lauterer (1963), 


B. salicivora TeM Pd A C ? L Salix Gegechkori (1984), 

(Reuter) 


Conci et al. (1996a, 

1996b)




Lerp former 

Gall 






Plant type 


Triozini B. striola (Flor) TeM Pd A C 2? L Salix Gegechkori (1984), 


Conci et al. (1996a, 

1996b) 

M/TeM G A C 7–10 S D Allium Tremblay (1958, 1961 (as 

nigricornis), 1965a, 

1965b), Annunziata and 

Clemente (1980), Conci 

et al. (1996) 

TeM H A C 2–3 L D Daucus Biase (1983), Lauterer 


(1996) 

TeM Pd/C A C 1 S D Rubus Sirrine (1895), Smith 

(1911), Felt (1906), 

Petersen (1923), Mead 

(1966a), Stuart (1991) 

TeM Pd/C A C 1 L Rubus Conci and Tamanini 

(1984b, 1986b), Conci 

et al. (1996) 

TrS Pe L L 1 L El Populus Mathur (1935), Beeson 

(1941) 

B. tremblayi 

(Wagner) 


B. trigonica 


Phylloplecta 

tripunctata 

(Fitch) 

P. trisignata 

(Löw) 

Egeirotrioza ceardi 

(Bergevin)



Lerp former 

Gall 






Plant type 


TrS Pe L S 1 S Es Populus Mathur (1935, 1975) 

E Pe L S 1 St Es Populus Pedata (1998) 

TeM Pe A L/S C 1 L R Eleagnus Miyatake (1978) 





TeD H A ? 1 ? Gegechkori (1984) 

TeM H L S 1 S Bupleurum Lauterer (1979, 1991) 

TeM H L S 2 S Bupleurum Lauterer (1965, 1979, 

1991) 

TeM Pd E S 1 L R Rhamnus Sampo (1975), Lauterer 


(1992), McLean (1993, 

1994, 1998), Conci et al. 

(1996) 

Triozini E. bifurcata 

(Mathur) 

E. populi 

(Horvath) 

Epitrioza 

marginata 

Miyatake 

E. mizuhonica 

Kuwayama 

E. yasumatsui 

Miyatake 

Eryngiofaga 

babugani 


E. hungarica 

(Klimaszewski) 

E. lautereri 


Trichochermes 

walkeri 

(Foerster)




Lerp former 

Gall 






Plant type 


TrS Pe ELA L M L P Trichilia Brown and Hodkinson 


TrS Pe L L 1 L El Psidium Butignol and Pedrosa 

(2003) 

Triozini Leuronota 

trichiliae Brown 

and Hodkinson 

Neotrioza tavearesi 

Crawford 

Trioza sensu lato 

TeM H A C 1? L Achillea Gegechkori (1984), 



T. abdominalis 

Flor 


T. agrophila Löw TeM H A C ? L Cirsium Gegechkori and 





T. alacris Flor M Pe A S 1–4 L R Laurus Essig (1917), Weiss (1917), 

Lizer (1918), Weiss and 

Dickerson (1921), 

Borelli (1920), Miles 

(1928), Sampo (1977), 

Conci and Tamanini 

(1985b), Ramirez 

Gomez (1958), de 

Meirleire (1971), 


Conci et al. (1996)



Lerp former 

Gall 






Plant type 



Conci et al. (1996) (as 

TeM H A C 1 L Anthriscus, 

Angelica 

Triozini T. anthrisci 

Burckhardt 

pallida) 

TeM H A S 1 S D Daucus Lundblad (1929), Bey 

(1931) (both as 

viridula), Balachowsky 

and Mesnil (1936), 

Laska (1964,1974), 

Rygg (1977), 


Ramert and Nehlin 


(1992), Ellis and 

Hardman (1992), Conci 

et al. (1996), 

Kristoffersen and 

Anderbrandt (2007) 

M Pd/Pe A C 1? L P? Rapisarda (1993b) 

T. apicalis 

Foerster 



TeM Pd A S 1 L Hippophae Conci and Tamanini 

(1984c) 

TeM Pe L L 1 L P Camphora Sasaki (1910), Sorin 

(1959a) 

T. apicula 

Rapisarda 

T. binotata Conci 

and Tamanini 

T. camphorae 

Sasaki




Lerp former 

Gall 






Plant type 


André (1878), 



T. cerastii (L.) TeM C A C 1 S D Cerastium Conci et al. (1996) 

TeM H/T A or S C 1 to M L D Centranthus, 

(ELA) 

Valerianella 

Triozini T. centranthi 

(Vallot) 


T. chenopodii TeM H/T A S 2–5 L D Chenopodium, Lauterer (1982), Baloch 

Reuter 

Atriplex, and Ghaffar (1984), 

Halimione Ossiannilsson (1992), 


T. chrysanthemi TeM H A C 1 L P Chrysanthemum Conci and Tamanini 

Löw 


(1996) 

T. cinnamomi TeM Pe ELA L 1 to M L El Cinnamomum Miyatake (1969), 

Boselli 

Rajapakse and 

Kulasekera (1982) 

T. cirsii Löw TeM H A C 1 L Cirsium Conci and Tamanini 

(1990) 

T. diospyri TrS Pd E S 2+ L R Diospyros Mead (1966b) 

(Ashmead)



Lerp former 

Gall 






Plant type 


L Citrus Moran and Blowers 

(1967), Moran (1968a, 

1968b), Catling and 

Annecke (1968), 

Catling (1969a, 1969b, 

1970, 1971), van 

Vuuren and Moll 

(1984), van den Berg 

and Villiers (1987), 

Samways (1987), van 

den Berg and Deacon 

(1988), van den Berg 

(1990), van den Berg, 

Anderson, et al. (1991), 

van den Berg, Deacon 

and Steenekamp (1991), 

van den Berg, Deacon 

and Thomas (1991a, 

1991b), Messi and 

Tamesse (1999), 

Tamesse and Messi 

(2004) 

TrS Ps ELA L M up 

to 8 

Triozini T. erytreae (Del 

Guercio) 






Lerp former 

Gall 






Plant type 


L P Syzygium Morgan (1984), Downer 

et al. (1991), Mead 

(1994), Dahlsten et al. 

(1995), Young (2003) 

TrS Pe ELA L M 

(3–5+) 

Triozini T. eugeniae 

Froggatt 


T. flavipennis TeM H A C 1 L P Aegopodium Löw (1880), Conci et al. 

Foerster 

(1996) 

T. fletcheri minor TrS Pe ELA L C L El Terminalia Mathur (1935), Beeson 

Crawford 

(1941), Mani (1948), 

Das et al. (1988) 

T. galii TeM H A C/LL 1+? S/L D/R Galium, Boselli (1929b), 

Aperula Burckhardt and 


T. hirsuta TrS Pe E S 2 L R Terminalia Mathur (1935, 1975), 

(Crawford) 

Beeson (1941), Mani 

(1948), Dhiman and 

Singh (2003, 2004) 

T. ilicina (De M Pe L L 1 L P Quercus Conci and Tamanini 

Stefani Perez) 

(1985c), Rapisarda and 

Belcari (1999), Conci 

et al. (1996) 

T. jambolanae TrS Pe ELA L 6–8 L El Syzygium Raman (1991) 

Crawford



Lerp former 

Gall 






Plant type 




Triozini T. kiefferi Giard M Pe A T/S 1 L El Rhamnus Rapisarda (1989a), Conci 

et al. (1996) 

T. laserpitii TeM H A C 1 L Laserpitium Burckhardt and Lauterer 



Lauterer 

(1996) 

T. machilicola TeM Pe L L 1 L P Machilus Miyatake (1968a) 

Miyatake 

T. magnisetosa TeM Pd A ? 2 L Rhamnus Gegechkori (1984) 


T. malloticola TrS Pe L L 2–3 L El Mallotus Mathur (1935, 1975), 

(Crawford) 

Beeson (1941), Mani 

(1948) 

T. magnicauda TrM Pe ELA L 9–11 L Diospyros Chang et al. (1995) 

Crawford 

T. magnoliae TrS Pe L L 1 L P Magnolia, Mead (1963), Leege (2006) 

(Ashmead) 

Persea 

T. munda Foerster TeM H A C 1? L P Knautia, Gegechkori (1984), 

Succisa, Ossiannilsson (1992), 

Scabiosa Conci et al. (1996) 

T. nana 

TeM H A ? ? 1 L Valeriana Gegechkori (1984) 

Gegechkori




Lerp former 

Gall 






Plant type 



Triozini T. neglecta TeM Pd A ? ? 2 L Eleagnus Lauterer and Janicek 


(1990), Lauterer (1993a) 

T. obsoleta TrS Pe L L 3 L El Diospyros Vaishampayan and 

Buckton 

Bahadur (1980) 

T. pitiformis TrS Pe L L 4 L P Mallotus Mathur (1935, 1975) 

Mathur 

T. proxima Flor TeM H A C 1 L P Hieracium Conci et al. (1996) 

T. rapisardai Conci TeM H A C 1 L Laserpitium Conci and Tamanini 

and Tamanini 

(1984d, 1988), Conci 

et al. (1996) 

T. remota Foerster TeM Pd A C 1 L P Quercus Sorin (1959b), Gegechkori 

(1984), Lauterer (1991), 


T. rhamni TeM Pd A C 2 L P Rhamnus Löw (1877), Gegechkori 

(Schrank) 

(1984), Lauterer (1991), 


T. rotundata Flor TeM H A C 1 L/St P Cardamine Gegechkori (1984), Conci 

(sensu 

and Tamanini (1987, 


1991), Conci et al. 

Lauterer) 

(1996), Burckhardt and 

Lauterer (2002)



Lerp former 

Gall 






Plant type 




Triozini T. rumicis Löw TeM H A C 1 F F Rumex Sampo (1975), 



T. saxifragae Löw TeM H/G A C 1–2 L Saxifraga Conci and Tamanini 

(1986c), Lauterer 


(1996) 

T. schrankii Flor TeM H A C 1 L Astrania Conci et al. (1996) 

T. scottii Löw TeM Pd/G A C 1 L R Berberis Sampo (1975), 



T. senecionis TeM H A C 1 L Senecio, Gegechkori (1984), Conci 

(Scopoli) 

Adenostyles et al. (1996) 

T. soniae M Pd A C 1 L P Quercus Rapisarda (1993b), Conci 

Rapisarda 

et al. (1996) 

T. tabebuiae TrR Pe L L M L R Tabebuia De Queiroz Santana and 

Santana and 

Burckhardt (2001) 

TeM H A C 1 L F Valeriana Burckhardt et al. (1991), 

Conci and Tamanini 


(1996) 

Burckhardt 

T. tripteridis 

Burckhardt et al.




Lerp former 

Gall 






Plant type 


Triozini T. urticae (L.) TeM H A C 1–4 L Urtica Lal (1934), Zhangeri 

(1954), Onillon (1969), 

Davis (1973), Sampo 




(1996) 

TeD H E S 1 L Valeriana Gegechkori and 



TeM H A C ? L Cirsium Gegechkori (1984), 


TeM Pe ELA L 2–5 L Pittosporum Carter (1949) 

T. valerianae 

Gegechkori 

TrS Pe L L 2 L El Litsaea Mathur (1935), Beeson 

(1941), Mani (1948) 

TrS Pe L L 1–2 L El Ficus Mathur (1935), Beeson 

(1941), Mani (1948), 

Abbas (1967), Negi and 

Bisht (1989) 

TrS Pe L L 1 L El Buchanania Thenmozhi and 

Kandasamy (1992) 

T. viridula 

(Zetterstedt) 

T. vitreoradiata 

(Maskell) 

Pauropsyllini Pauropsylla 

beesoni Laing 

P. depressa 

Crawford 

P. longispiculata 

Mathur



Lerp former 

Gall 






Plant type 



Pauropsyllini P. purpurescens TrS Pe L L 3 L El Ficus Mathur (1935, 1975) 

Mathur 

P. trichaeta Petty M Pe ELA L M L P Ficus Awadallah and Swailem 

(1971) 

P. udei Rübsaamen TrS Pe ELA L M L El Ficus Hill (1982) 




The relationship between the development rate of non-diapausing larvae and 

temperature is asymptotic for species such as Agonoscena pistaciae, Diaphorina citri, 

Cacopsylla pyri and Cacopsylla pyricola within the temperature range 5–35uC 

(McMullen and Jong 1977; Kapatos and Stratopoulou 1999; Liu and Tsai 2000; 

Nakata 2006; Mehrnejad and Copland 2006b). Development commences at the 

lower temperature threshold for development, rises approximately linearly to a 

maximum as temperature increases, but then falls back at higher temperatures, 

presumably in response to increasing thermal stress. By contrast, other species such 

as Psyllopsis fraxini, Mesohomotoma tessmanni and Heteropsylla cubana appear to 

show a linear response, although the maximum experimental temperatures tested 

(30–32uC) were lower than in the previous examples and thus probably less stressful 

(Nguyen 1970a; Messi 1983b; Patil et al. 1994; Geiger and Gutierrez 2000). A similar 

difference in response occurs between the development rate of eggs (linear) and 

larvae (asymptotic) of C. pyri over an identical temperature range, suggesting a 

divergence in thermal sensitivity of their respective development rate at higher 

temperatures (Kapatos and Stratopoulou 1999). 

Temperature-specific development rates may also differ significantly among 

instars, although there appears to be little consistency in the trend. For example, in 

Ctenarytaina thysanura and Trioza urticae, at a given temperature, speed of 

development is highest in the early instars and progressively slows in the later instars 

(Onillon1969; Mensah and Madden 1993b). By contrast, development rates in other 

species such as Heteropsylla cubana, Mesohomotoma tessmani, Trioza magnicauda, 

Trioza erytreae, Psyllopsis fraxini, Cacopsylla pyricola and Diaphorina citri, appear 

highest in the intemediate instars (2–4) (Moran and Blowers 1967; Nguyen 1970b; 

An et al.1996; McMullen and Jong 1977; Messi 1983b; Patil et al. 1994; Chang et al. 

1995; Geiger and Guttierez 2000; Tsai and Liu 2000; Liu and Tsai 2000). 

The lower temperature threshold for larval development is comparatively low 

relative to ambient temperatures in tropical/subtropical species such as Heteropsylla 

cubana (9.6uC), Trioza erytreae (8.6–9.2uC) and Diaphorina citri (10.9–11.7uC) but 

significantly higher than in temperate species such as Strophingia ericae (c. 3uC), 

Trioza urticae (,6uC) and Cacopsylla pyricola (2–3uC) (Blowers and Moran 1968; 

Hodkinson et al. 1999; Kapatos and Stratopoulou 1999; Liu and Tsai 2000; Geiger 

and Gutierrez 2000). 

Field development times from hatching egg to emerging adult in nondiapausing 

tropical/subtropical species including Allocarsidara malayensis, 

Mesohomotoma tessmani, Diclidophlebia xuani, Heteropsylla cubana, Trioza 

erytreae and Trioza magnicauda typically range between 9.5–23 days (Blowers 

and Moran 1968; Messi 1983b; Gadug and Hussein 1987; Patil et al. 1994; Chang 

et al. 1995; Tsai and Liu 2000). However, some less typical tropical species, such as 

Euphalerus clitoriae on Clitoria may take up to 34 days to complete development 

(Junior et al. 2005). By contrast, development times of equivalent warm to cool 

temperate species, including Euphyllura olivina, Anomoneura mori, Asphagidella 

buxi, Cacopsylla melanoneura, C. pyricola and C. ambigua, typically span around 

22–44 days (Lal 1934; Loureiro Ferriera 1946; Kuwayama 1971). Development, 

however, can be significantly slower at temperatures just above the developmental 

threshold, extending to 190 days in T. urticae at 6uC, 56 days for Psyllopsis fraxini 

at 15uC and 47 days for Cacopsylla pyricola at 10uC (Onillon 1969; Nguyen 1970b; 

McMullen and Jong 1977).



Response to high temperature and drought 

Psyllids in tropical/subtropical and desert ecosystems are often exposed to 

potentially lethal high temperatures, particularly when such temperatures are 

coupled with low humidity to produce a high Saturation Deficit Index (SDI). High 

temperatures/low humidity are known to influence strongly life cycle completion in 

several psyllid species, where it results in reduced fecundity, increased mortality and 

slower rates of development at temperatures above the optimum for the species in 

question. It may also limit the distribution of the psyllid within the broader range of 

its potential host plant. 

Effect on mortality, reproduction and longevity 

The link between high temperature, SDI and mortality is particularly welldocumented 

in Trioza erytreae on Rutaceae, for which models have been produced 

to predict population densities from these climatic variables by defining particularly 

lethal SDI values (Moran and Blowers 1967; Catling and Annecke 1968; Catling 

1969a, 1969b; van Vuuren and Moll 1984; Samways 1987; van den Berg, Anderson 

et al. 1991; Tamesse and Messi 2004). Similar links between high temperature and 

population crashes have been observed in Heteropsylla cubana (.36uC) and 

Glycaspis baileyi on Eucalyptus, notwithstanding that larvae of the latter species 

secrete a protective covering or lerp (Moore 1961; Yasuda and Tsurumachi 1988; 

Geiger and Gutierrez 2000). 

The relationship between SDI and mortality at a given standard high 

temperature, however, is not linear. At a low SDI Acizzia russellae on Acacia died 

from thermal shock associated with low evaporative cooling of host leaves. Survival 

rose to an optimum at a moderate SDI as evaporative cooling became more effective 

but then declined as the SDI increased and desiccation became significant (Hoffman 

et al. 1975). Trioza hirsuta on Terminalia showed similar optimal survival within the 

range 70–90% relative humidity (Dhiman and Singh 2003). 

Among temperate species such as Cacopsylla pyricola, egg output per female and 

longevity are reduced at temperatures (,35uC) that exceed the optimum of 26.7uC. 

Similar suppression of egg production at high summer temperature is found in 

Cacopylla pyri (Stratopoulou and Kapatos 1995b; Souliotis and Broumas 1998). 

Even in tropical species, such as Diaphorina citri, the optima for oviposition and 

development are 25–28uC, with larvae failing to develop at 33uC (Liu and Tsai 2000). 

Gall-forming species, despite living within humidity-buffered galls, are not 

immune from a high SDI, with species such as Euphalerus ostreoides on 

Lonchocarpus suffering high mortality among young larvae before gall formation 

(Ferreira et al. 1990). However, some species in cool temperate environments such as 

Craspedolepta nebulosa and C. subpunctata appear physiologically capable of 

withstanding at least short-term exposure, as older larvae, to high temperature 

(40uC), provided high humidity is maintained (Bird and Hodkinson 1999). 

Often the precise choice of oviposition site on a plant determines whether or not 

a psyllid egg survives a low SDI. Those of Cacopsylla pyricola, for example are less 

susceptible to desiccation when laid along the mid vein rather than on the leaf lamina 

(Horton 1990a). This is probably linked to differences in the relative availability of 

water within the leaf tissue for absorption through the basal pedicel of the psyllid 

egg, which is inserted into the plant tissue (White 1968; Conci 2000).



Effects on distribution 

Temperature and humidity may thus affect both the absolute distribution and the 

relative breeding success of a psyllid species across its range. Megatrioza species on 

Pritchardia in the Hawaiian Islands are confined to altitudes above 425m, where 

temperatures are lower and humidity is higher (Uchida and Beardsley 1988). The 

range of Trioza erytreae in South Africa is limited by high temperature/SDI and even 

within this restricted range populations tend to increase with altitude (Catling 1969b; 

Green and Catling 1971; Human and Bedford 1985). 

Positive impact of drought 

Not all effects of low water availability and high temperature are negative for 

psyllids. Periods of atypically low winter rainfall, for example, produce water stress 

in Eucalyptus fasciculosa that is strongly correlated with subsequent population 

outbreaks of the psyllid Cardiaspina densitexta (White 1969, 1971). Stress in this 

instance leads to increased mobilization of soluble nitrogen within the leaves, which 

in turn enhances their suitability for larval development (White 1969, 1971). The 

effect is similar to that observed in Cacopsylla pyricola when its host plant is 

fertilized with nitrogen (Pfeiffer and Burts 1983, 1984; Daugherty et al. 2007). 

Seasonal polymorphisms 

Morphological differences 

Several species of psyllid display environmentally determined seasonal polymorphisms 

as part of their life cycle. This has, in the past, resulted in the seasonal forms 

being described as distinct species. Such polymorphisms are often closely linked to 

diapause and have major implications for life history completion, involving key 

differences in performance, life history parameters and dispersal characteristics in 

the species concerned. These implications are discussed in detail later in the context 

of the factors such as day length and temperature that determine onset and breaking 

of diapause. Seasonal polymorphisms occur in the adults of several multivoltine 

species within a number of distantly related taxa, including Agonoscena pistaceae on 

Pistacia, Cacopyslla pyricola, andC. pyri on Pyrus, Celtisaspis japonica on Celtis, 

Bactericera acutipennis on Comarum and Trioza chenopodii on various 

Chenopodiaceae (Bonnemaison and Missonnier 1955a; Wong and Madsen 1967; 

Oldfield 1970; Nguyen 1972a, 1985; Miyatake 1980; Lauterer 1982; Mustafa and 

Hodgson 1984; Rieux and d’Arcier 1990; An et al. 1996; Mehrnejad 2002; Mehrnejad 

and Copland 2005). Polymorhism may simply involve marked seasonal differences in 

overall size (Acizzia uncatoides and A. acaciaebaileyani on Acacia) or colour (Acizzia 

spp. and Bactericera perrissii on Artemisia) among generations (Koehler et al. 1966; 

Lauterer 1982; Rapisarda 1993a). More frequently it additionally involves 

differences in such things as the relative size, shape and venation of the forewing, 

the presence or intensity of forewing colour patterns, the distribution and density of 

surface spinules in the forewing cells, minor differences in the shape of the 

terminalia, dark or light body colouration, and the relative length of the antenna and 

its component segments. In Cacopsylla pyricola, C. pyri and A. pistaceae the morphs 

usually consist of a smaller lighter coloured spring form with little or less-intense 

wing colour pattern and an autumn form that is larger and darker, with a distinctive



darker wing colouration or pattern. Morph determination is, however, not absolute 

and intermediate generations often display transitional characteristics between the 

extremes, or a few autumn forms may be produced even in summer generations 

(Mustafa and Hodgson 1984; Nguyen 1985; Rieux and d’Arcier 1990; Mehrnejad 

and Copland 2005). There is evidence for C. pyri that different features of the 

polymorphism, such as wing pattern or body colour are controlled to different 

extents by particular temperature and photoperiod exposures acting during the 

larval stages (Nguyen 1972a). In contrast to the aforementioned species, Trioza 

chenopodii unusually has its darker autumn form characterized by shorter and 

broader wings (Lauterer 1982). The darker wing-patterned autumn morph of 

Pachypsylla japonica additionally shows strong sexual dimorphism in wing pattern. 

The adaptive significance of this is obscure, but such sexual pattern dimorphism also 

occurs sporadically in both other temperate (Livilla pogii on Genista) and tropical 

(Euphalerus fossiconis, host unknown) species (Conci and Tamanini 1984a; Brown 

and Hodkinson 1988). Other species, such as Crastina loginovae on Tamarix, show 

similar strong sexual dimorphism in general body colouration (Conci and Tamanini 

1983). 

Seasonal colour change in long-lived adults 

Long-lived adults of many temperate univoltine species undergo marked colour 

changes throughout the season. This may have adaptive significance through 

camouflage (Sutton 1983). Changes can occur gradually over several months and are 

often associated with a reproductive diapause. In genera such as Cacopsylla and 

Psylla, for example, the general body colouration changes gradually from pale 

colours such as green or yellow to deep red, brown and black. Adults of Cacopsylla 

peregrina, for instance, are bright green on emergence in spring, matching the colour 

of the leaves of their host plant, Crataegus monogyna, on which they are initially 

found. As the season progresses sexually maturing adults move from the leaves on to 

the darker stems as a prelude to oviposition and this is accompanied by a change in 

body colouration to a more cryptic brown and red (Sutton 1983). 

Consequences of size differences 

Temperature-induced size polymorphism resulting from varying developmental rates 

has strong implications for life history completion at the edge of psyllid species’ 

ranges. For example, Craspedolepta nebulosa and C. subpunctata are univoltine 

species feeding on Epilobium angustifolium. Both are widely distributed in the 

temperate northern hemisphere. C. nebulosa shows developmental flexibility by 

reducing its body size and increasing its developmental temperature reaction norm as 

the day degrees available for larval development decrease along an altitudinal 

transect. C. subpunctata shows no such flexibility and is thus restricted to lower 

altitudes, thereby occupying a smaller portion of the host-plant range than C. 

nebulosa (Bird and Hodkinson 2005; Hodkinson and Bird 2006b). Atypically high 

temperature may also affect psyllid size. Both egg length and wing length of 

Heteropsylla cubana on Leucaena in Thailand decreased with rising temperature over 

the range 20–30uC and this was thought to be a partial explanation for a population 

crash during unseasonably hot weather (Geiger and Gutierrez 2000).



Induction of seasonal morphs 

The production of different seasonal morphs is primarly controlled by day length, 

with temperature often playing a secondary role. For example C. pyricola eggs reared 

experimentally under short days (LD 12:12 h) produce autumn/winter-form adults; 

those reared under long day length (LD 16:8 or 18:6 h) produce summer forms 

(Mustafa and Hodgson 1984). The precise day length inducing the winter form 

varies, however, between studies and localities, with winter forms being produced at 

day lengths between 11 and 14 h in California and British Columbia respectively 

(Wong and Madsen 1967; Oldfield 1970; McMullen and Jong 1976). Day length acts 

on the early larval stages, but larvae become progressively less susceptible to a 

sudden switch in day length as they develop, becoming insensitive by the fourth or 

fifth instar (Mustafa and Hodgson 1984; An et al. 1996). The process at the relatively 

high experimental temperatures used appears relatively insensitive to temperature 

(An et al. 1996). Seasonal polymorphism in C. pyri and Agonoscena pistaceae 

appears to be under similar control, with short day length (LD 12:12), but coupled 

with low temperature (15uC) acting on instars 1–3 to produce the autumn/winter 

form and long day length linked to higher temperatures (25uC) resulting in spring/ 

summer forms (Bonnemaison and Missonnier 1955a, 1955b; Nguyen 1972a; 

Mehmejad and Copland 2005). 

Significance of diapause 

For tropical multivoltine psyllids species living in non-seasonal environments, such 

as Diaphorina citri in the Philippines, the host plant Citrus spp. remains suitable for 

psyllid development throughout the year and life cycle progression is usually 

uninterrupted (Bigornia and Obana 1974). However, for species living in seasonal 

environments, close phenological synchrony of development with that of the host 

plant is a prerequisite for successful life cycle completion. Diapause provides the 

timing and synchronization mechanism through which psyllids are able to survive 

unfavourable periods, such as extended periods of cold or drought, when their host 

plant becomes unfavourable for development. Diapause, which involves a slowing 

down or cessation of development, may occur in one or more of the egg, larval and 

adult stages, depending on species and circumstances. It is usually controlled by 

environmental cues, such as photoperiod and temperature, which signal changes in 

the favourability of the external environment that will, when mediated through the 

host plant, affect psyllid development. The mechanisms that instigate and control 

adult diapause are well understood for a few economically important multivoltine 

psyllids such as Cacopsylla pyricola and C. pyri but remain unknown for the vast 

majority of species. Interestingly, diapausing adult C. pyricola are more insecticide 

tolerant than non-dipausing adults and this has implications for population contol of 

economically important species (Unruh and Krysan 1994). 

Developmental diapause in eggs and larvae 

Egg diapause occurs most frequently in univoltine species associated with deciduous 

trees and shrubs in which eggs laid on exposed shoots and branches one year 

overwinter, and hatch the following year. Examples include Psyllopsis fraxini on 

Fraxinus, Cacopsylla peregrina on Crataegus and Psylla alni on Alnus (Lal 1934;



Nguyen 1970b; Bonnemaison 1956). Overwintering by diapausing larvae on bare 

shoots is less frequent but not unknown; Calophya triozomima, for example, 

overwinters at the base of the bud of its host Rhus (Wheeler and Rawlins 1993). 

Larval winter diapause is more frequently found in free-living species that overwinter 

on evergreen hosts such as Strophingia ericae on Calluna, Livilla magna on Genista 

and Asphagidella buxi on Buxus (Nguyen 1968; Conci et al. 1993; Miles et al. 1998; 

Butterfield et al. 2001). Larvae cease development in the autumn and recommence in 

spring. 

This period of suspended development may in some species also embrace a large 

part of the previous summer. Several leaf-gall forming species, for example, Trioza 

camphorae on Camphora, Trioza cinnamomi on Cinnamomum, T. machilicola on 

Machilus, andT. obsoleta on Diospyros hatch in spring and develop to early-stage 

larvae before entering diapause: development to adult only recommences the 

following spring (Sorin 1959a; Miyatake 1968a, 1969; Vaishampayan and Bahadur 

1980). A similar extended larval diapause is found in several Craspedolepta species 

including C. nebulosa and C. subpunctata on Epilobium, but in these latter species 

there is a larval migration onto the roots or the overwintering shoots of their 

herbaceous perennial host (Bird and Hodkinson 1999, 2005). In these examples 

diapause serves to retard the production of adults and synchronize the life cycle of 

the psyllid with the optimum spring period for oviposition on the host. Summer 

larval diapause as in Trioza saxifragae on Saxifraga and species of Acaerus on 

Calligonum probably facilitates summer survival in particularly dry habitats 

(Loginova 1970, 1976; Lauterer 1993a). By contrast, diapause in T. remota and T. 

soniae on Quercus leaves and Trioza kiefferi on Rhamnus, which delay adult 

emergence until autumn, probably corresponds with a period when mature host 

leaves have become unsuitable for development. Subsequent leaf senescence in 

autumn then releases the soluble amino acids required for development through to 

overwintering adult (Conci et al. 1996). 

Reproductive diapause in adults 

Adult reproductive diapause, in which egg development by females is postponed, 

again achieves similar ends in different species. In several univoltine species of 

Cacopsylla sensu stricto, such as C. mali on Malus, C. sorbi on Sorbus and C. 

peregrina on Crataegus, and Psylla species such as P. betulaenanae on Betula and P. 

borealis on Alnus, adults emerge in late spring but egg development and oviposition 

on stems and branches is delayed until autumn (Brittain 1922a; Sutton 1983; 

Hodkinson and Bird in press). A possible advantage of postponed oviposition is that 

eggs are not exposed to predation or desiccation throughout the summer, although 

this must be offset against the probability of reduced female survival throughout this 

period. 

Many psyllid species overwinter as adults, either on their host or on shelter 

plants (see later), and reproductive diapause ensures that eggs are not matured and 

laid until the following spring when the host becomes suitable for larval 

development. Thus, species that move onto shelter plants during winter undergo 

an extended diapause that delays sexual maturation of eggs until the flight to and the 

return from the winter host are completed. In multivoltine species such as Cacopsylla 

pyricola, Cacopsylla pyri and Bactericera nigricornis it is the autumn generation that



undergoes this reproductive diapause (Nguyen and Ledoux 1973; Nguyen 1975; 

Mustafa and Hodgson 1984; Krysan 1990; Krysan and Higbee 1990; Lyoussoufi 

et al. 1994; Horton et al. 1998). Many adult overwintering psyllids, including, for 

example, several Cacopsylla species on Salix, Livia junci on Juncus, Aphalara species 

on Polygonaceae, Euphyllura phillyreae Foerster on Olea and Togepsylla matsumurana 

on Lindera are, however, univoltine (Heslop-Harrison 1949b; Miyatake 1970; 

Lauterer 1976, 1979; Prophetou and Tzanakakis 1977 (as olivina); Hill and 

Hodkinson 1996; Tzanakakis 2003; Del Bene et al. 1997). They emerge in the 

previous spring or early summer, necessitating an even longer period of reproductive 

diapause to ensure host synchrony the subsequent year. Diapause may also play a 

role in survival during summer dry periods. Diaphorina lycii on Sardinia has up to 

five generations per annum, but breeding on the host Lycium is concentrated into the 

wetter spring and autumn and adults undergo reproductive diapause during the 

intervening summer (Rapisarda 1990a). 

Control of diapause 

Egg and larval diapause 

Little is known about the control of diapause in psyllid eggs and larvae. Among the 

few species studied, the univoltine Asphagidella buxi on Buxus overwinters in 

southern France as a first instar larva beneath the chorion of the egg from which it 

has emerged in autumn. September–December represents a period of true diapause 

initiated by cues unknown (Nguyen 1968). This is followed by a reactivation phase 

that leads up to the moult to second instar in March. Prolonged exposure to 

temperatures between 0–10uC for 10–30 days is necessary to break diapause but once 

broken the development rate during the reactivation phase is positively correlated 

with temperature (Nguyen 1968). Developmental inhibition, acting at different 

stages of larval development of Strophingia ericae on Calluna at high or low 

altitudes, controls whether the species undergoes a one or two year life cycle. At both 

altitudes eggs hatch over an extended summer period. In annual lowland 

populations, which overwinter predominantly in instar 3, long days (LD18:6 h) 

retard development through instars 1–3, and development through to adult is 

delayed until the following spring. Instars 4 and 5 respond positively to elevated 

temperature and long days, from mid-winter onwards. In biennial upland 

populations development is slower at lower temperatures and larvae overwinter 

predominantly in instars 1 and 2. Development continues the following year but is 

inhibited by short autumn day length (LD 12:12 h) in instar 5, ensuring synchrony 

within the population and adult emergence in spring of the following year (Miles 

et al. 1998; Butterfield et al. 2001). 

Adult diapause 

In seasonally polymorphic multivoltine species, such as C. pyricola, C. pyri and A. 

pistaciae, the factors such as photoperiod and temperature that induce the autumn 

morphological forms are the ones that simultaneously initiate ovarian diapause in 

overwintering female adults (Wong and Madsen 1967; Oldfield 1970; McMullen and 

Jong 1976; Mustafa and Hodgson 1984; Mehmejad and Copland 2005). Less is 

known about the factors inducing ovarian diapause in spring emerging adults,



although photoperiod, temperature and possibly host-plant condition are again 

likely to be involved. In Euphyllura straminea on Olea a mean temperature of .20uC 

rather than photoperiod or host-plant quality is thought to induce summer diapause 

(Mustafa and Najar 1985). For overwintering adult female psyllids ovarian diapause 

is usually broken at some point during the winter to be followed by a period of 

quiescence at low temperature when ovarian development continues to be depressed 

but once spring temperatures rise then egg development takes place. Adult longevity 

during this late-winter period may, however, decline as temperatures rise (Hill and 

Hodkinson 1996). 

For species with an extended long ovarian diapause commencing in the previous 

spring, such as Euphyllura phillyreae, then a succession of summer, winter and spring 

conditions are necessary to terminate diapause (Prophetou and Tzanakakis 1986; 

Tzanakakis 2003). A combination of increasing day length coupled with rising 

temperature during winter, however, is still necessary to break ovarian diapause in 

the univoltine Cacopsylla moscovita overwintering on Salix (Hill and Hodkinson 

1996). 

For multivoltine species such as C. pyricola and C. pyri the effectiveness of long 

photoperiod in breaking female diapause diminishes as the winter progresses and the 

importance of rising temperature increases (Nguyen 1964, 1967a, 1967b, 1968, 1975; 

Fields and Zwick 1975; McMullen and Jong 1976; Horton et al. 1998). However, in 

the latter species exposure to temperatures above 25uC breaks diapause irrespective 

of photoperiod. The temperature required to terminate ovarian diapause generally 

differs both within and among species and habitats, depending on the characteristic 

temperatures that the species normally experience and the relative length of the 

winter period. 

By contrast with the reproductively suppressed females, newly emerged males of 

the autumn diapausing form of C. pyricola have active sperm in the testes and 

seminal vesicles, but rates of insemination are depressed at short photoperiod (LD 

10:14). Initially, an exposure for 10 days at long photoperiod (LD 16:8) is required to 

release sexual activity but the exposure time required decreases as the winter 

progresses (Krysan 1990; Krysan and Higbee 1990). Repeated mating and 

insemination of females on the overwintering host is evidenced by the presence of 

multiple spermatophores (mean 5.3 to 16.5 per female), with each spematophore 

representing one copulation (Burts and Fischer 1967; Krysan 1990; Krysan and 

Higbee 1990). Psyllids collected from conifers on warm days during late winter show 

similar promiscuous tendencies suggesting that, for psyllids, the overwintering 

period is far from being a quiescent and relatively unimportant phase of the life 

cycle. Mating, however, does not always lead to insemination (Van den Berg, 

Deacon and Thomas 1991a). 

Mating, before or immediately after adult diapauses, usually ensures that egg 

development and maturation are completed ahead of the host plant becoming 

suitable for oviposition, provided the temperature is sufficiently high. This applies to 

both summer diapausing species such as Euphyllura straminea and winter diapausing 

species such as Cacopsylla moscovita, Cacopsylla pyricola and Euphyllura phillyreae 

(Prophetou and Tzanakakis 1977, 1986; Mustafa and Najar 1985; Lyoussoufi et al. 

1994; Hill and Hodkinson 1996; Horton et al. 1998). Mature eggs of C. moscovita 

first developed in the field, for example, 6 weeks before the Salix catkins on which 

they were to be laid (Hill and Hodkinson 1996).



The larger size of overwintering morphs of multivoltine psyllid species has 

implications for both reproductive performance and dispersal ability of individuals. 

There are often major differences in the main parameters of reproduction between 

summer and post-diapause winter morphs of the same species, including the length 

of the pre-reproductive and oviposition periods, the mean number of eggs produced 

per female and adult longevity. For example, optimum mean fecundity in 

Agonoscena pistaceae varied between 893 and 1087 eggs per female in summer and 

winter morphs respectively (Mehmejad and Copland 2005). The difference is even 

more marked in pear psyllids with corresponding figures for C. pyricola of 212 

(summer) and 486 (winter) in Canada and 387 and 486 in South Korea (McMullen 

and Jong 1977; Butt and Stuart 1986; An et al. 1996). C. pyri exhibits similar 

variation (342 and 471) (Nguyen 1970a; Kapatos and Stratopoulou 1996). 

The optimum temperature for maximum fecundity may also shift between 

generations to match the prevailing ambient temperature. In laboratory experiments, 

egg output per female of C. pyricola was optimal at 15.6uC in the winter form but 

maximal at between 21.1 and 26.7uC in the summer form (McMullen and Jong 

1977). The pre-reproductive period is generally shortest in summer forms, but 

longevity is greatest in winter forms. The net result of these variations is that egg 

output tends to be maximized at the start of the host-plant growing season. There 

may also be behavioural differences between the morphs, with summer forms 

showing a strong ovipositional preference for leaves but winter forms preferring 

dormant bud-bearing stems (Butt and Stuart 1986). 

Development of cold-hardiness 

Overwintering psyllids in temperate, montane and boreal habitats are frequently 

exposed, often over long periods, to sub-zero temperatures that may potentially 

damage or ultimately freeze the body tissues. Freeze tolerance is unknown among 

psyllids and survival depends on the ability of individual species, whether in the egg, 

larval or adult stage, to resist freezing by lowering the supercooling point (SCP) of 

their body tissues. Adult and larval stages may mitigate the effects of low air 

temperature to some extent by seeking out overwintering sites beneath a protective 

snow blanket or, in the case of adults, on evergreen trees such as conifers (Bird and 

Hodkinson 1999). 

Eggs 

Overwintering eggs, however, are often exposed on tree branches to the full rigour of 

winter. Those of Cacopsylla mali in Norway, for example, display a mean SCP that 

varies between 228.0uC and 238.8uC, depending on whether or not eggs have been 

acclimated at sub-zero (25uC) temperature (Skanland and Sömme 1981). This allows 

eggs to avoid freezing, even at the very low winter temperatures recorded. The lowered 

SCP is achieved partly by the synthesis of cryoprotectants such as glycerol within the 

egg, with highest concentrations found in midwinter (Skanland and Sömme 1981). 

Larvae 

Recorded mean SCPs for overwintering instars include Strophingia ericae 

(range5221.6 to 227.3uC), S. cinereae (223.6 to 223.7uC), Craspedolepta nebulosa



(221.6 to 223.5uC) and C. subpunctata (221.8 to 223.5uC) (Cannon 1983; Bird 

and Hodkinson 1999; Hodkinson et al. 1999). SCP was slightly lower in upland 

populations of S. ericae than lowland populations, although there was no 

difference between the mean SCP of the S. ericae and S. cinereae where they 

occurred together at the same site, despite the latter species being more typically 

Mediterranean than its congener. Similarly there was little variation in SCP of 

populations of C. nebulosa in lowland UK and Tromsø, northern Norway. SCPs of 

all species studied to date, despite their varying evolutionary and geographical 

origins, fall within a narrow range, suggesting that larvae may posses attributes 

that predispose them to surviving cold. Sap feeding, in particular, ensures that icenucleating 

food particles are absent from the gut. There is, however, evidence for 

all the aforementioned species and for Asphagidella buxi that the SCP should only 

be taken to indicate the lower limit of cold-hardiness (Nguyen 1969; Bird and 

Hodkinson 1999; Hodkinson et al. 1999). In both long and short time survival 

experiments at sub-zero temperatures, mortality accrues above the SCP as 

temperatures fall: mortality is related to the period of exposure as well as to 

temperature per se. Furthermore, prior acclimation at high sub-zero temperatures 

(25 or210uC) enhances survival of fifth-instar A. buxi larvae at 215uC compared 

with controls at 215uC. Survival at low temperatures in species such as A. buxi 

may differ among overwintering instars, with later instars performing better. 

However, in the aformentioned Strophingia and Craspedolepta species, such 

differences were not apparent (Bird and Hodkinson 1999). 

Adults 

Overwintering adults of A. buxi and Cacopsylla melanoneura are significantly less 

cold-hardy than eggs or larvae, as previously discussed. The SCP of C. melanoneura, 

for example, varied between 26.8 and 214.7uC when acclimated at up to 11 days at 

6uC compared with 211.1 to 215uC when acclimated at 27uC (Nguyen 1969, 

Jackson et al. 1990). SCP values for adults of the overwintering form of Cacopsylla 

pyricola (218 to 222uC), however, were comparable with larval values cited earlier 

and Trioza apicalis adults show high survival (71–87%) when exposed to 218uC for 

7 days (Rygg 1977; Horton et al. 1996; Lee et al. 1999). Freeze susceptibility, 

however, was markedly increased (SCP changed from 215uC to22–15uC) when C. 

pyricola was placed in contact with surface moisture or bacteria such as 

Pseudomonas syringi, which act as ice-nucleating agents (Horton et al.1996; Lee 

et al. 1999). 

One of the mechanisms by which freeze susceptibility can be lessened is for 

overwintering psyllids to reduce freezable body water content before the onset of 

winter, as occurs in adult C. melanoneura and Euphyllura straminea (Mustafa 1989b; 

Jackson et al. 1990). Psyllids that become active during winter and begin fluid 

feeding during temporary warm spells thus run the risk of lowering their resistance to 

cold. Even in non-feeding adults, metabolic production of water from stored fat 

reserves may again potentially increase cold susceptibility (Jackson et al. 1990; Hill 

and Hodkinson 1996). 

Psyllids have thus evolved a variety of mechanisms to prevent winter mortality in 

cold environments that appear largely independent of phylogeny.



Metabolic adaptations 

In passing through their life cycles, psyllids incur the metabolic cost of respiration: 

energy expended in maintaining body tissue becomes unavailable for growth, 

development and reproduction. It is thus advantageous to minimize basal 

metabolism during periods of seasonal inactivity or growth cessation, especially 

when this is linked to diapause. Metabolic energy expenditure for individual species, 

measured as oxygen uptake, is influenced significantly by ambient temperature, body 

size and sex (Krawczyk and Migula 1979; Migula et al. 1980). 

Adult male psyllids generally tend to be smaller and more active than females 

and, within any given species, have a higher metabolic rate per unit body weight. 

Similarly across adults of species representing the larger psyllid families Psyllidae 

and Triozidae there is a negative relationship between log respiration and log body 

mass, indicating that smaller species tend to respire less ‘‘efficiently’’ than larger 

species. 

There are, however outliers to this general pattern: Rhinocola aceris and Livia 

junci (Psyllidae) have much lower rates of metabolism than might be predicted from 

their body size, possibly indicating their more sedentary nature (Migula et al. 1980). 

When measured over the range 15–25uC an array of species belonging to Aphalara, 

Craspedolepta, Rhinocola, Livia, Psyllopsis, Arytaina, Psylla, Cacopsylla, Trioza, 

Trichochermes and Bactericera, genera with differing degrees of phylogenetic 

relatedness and contrasting life history patterns, all showed significantly increasing 

respiration with temperature. The rate of increase, however, varied significantly 

among species, resulting in considerable differences in metabolism among species at 

a given ambient temperature. 

While the species sample size is small, and the temperature range examined 

rather high, there is clear evidence for differences in metabolic rate among individual 

species with different life history adaptations (Migula et al. 1980). For example, 

widely distributed multivoltine species such as Bactericera nigricornis, Trioza urticae 

and Cacopsylla pyri tend to have higher metabolic rates than their univoltine 

congeners (Migula et al. 1980). Similarly, Aphalara species tend to have higher 

metabolism than the related Craspedolepta, which may reflect differences in their 

speed of development following overwintering as adults and larvae respectively. 

Among several species overwintering on conifers, such as Aphalara exilis and 

Bactericera nigricornis, metabolism is higher by between 20–38% during spring 

reproductive activity than in autumn before overwintering (Migula et al. 1980). 

Phenological synchrony with host-plant growth and host quality 

Under both temperate and tropical conditions a high degree of phenological 

synchrony between psyllid and host-plant growth is required for successful life cycle 

completion. Among temperate psyllids that overwinter as eggs, such as many 

Cacopsylla, Psylla and Psyllopsis species, egg hatch is generally timed to coincide 

with bud burst, although the precise mechanisms maintaining this synchrony are 

poorly understood (Nguyen 1970b; Lal 1934). In Cacopsylla mali and C. peregrina, 

for example, on Malus and Crataegus respectively, larvae hatch within a few days of 

the first buds breaking and move on to the newly developing plant tissues, especially 

the flower clusters (Przybylski 1970; Jonsson 1983; Sutton 1984; Lal 1934). This 

synchrony is generally strictly maintained among different sites and years



(Przybylski 1970). The importance of such close synchrony for the psyllids is 

emphasized in Crataegus by the rapid decline in the quality of their food resource, 

with soluble nitrogen concentrations of shoots and leaf clusters falling from around 

0.5 mg N dry weight 21 at bud burst to less than 0.1 mg N dry weight 21 1 month later 

(Sutton 1984). Timing of egg hatch in Homotoma ficus on Ficus appears to determine 

subsequent larval abundance (Gençer et al. 2007). Cacopsylla ambigua on Salix, in 

contrast to the aformentioned species, is unusual in that eggs hatch well ahead of 

bud burst and the larvae remain quiescent beneath the bud scales (Lauterer 1999). 

Non-gall-forming univoltine psyllids that overwinter as adults and which already 

contain fully developed eggs by early spring, such as Cacopsylla moscovita mentioned 

earlier, have the advantage of ovipositing directly onto newly emerging foliage as 

soon as it appears. This is a more precise procedure with less natural wastage than 

one involving small newly emerged larvae seeking out actively growing tissues. Eggs 

laid, however, may then take further time to hatch. Cacopsylla affinis and C. 

melanoneura larvae, for example, emerge 7–14 days after C. peregrina on the same 

host (Sutton 1984). This direct spring oviposition strategy is employed by a diversity 

of species including Gyropsylla ilicis on Ilex, several Aphalara species on 

Polygonaceae and is probably best exemplified by Cacopsylla species feeding on 

willow (Salix) (Mead 1983; Hodkinson et al. 1979; Hill and Hodkinson 1995; Hill 

et al. 1998; Hodkinson 1997). 

Many of these latter species develop on female Salix catkins and life cycle 

completion within a narrow phenological window is vital. Willow catkins are of 

short persistence, developing early in the year before drying out and dehiscing once 

the seed has developed. Catkin ‘‘life’’ for six species of willow in northern Alaska 

varied between 37–43 days, depending on species. The associated psyllids, Cacopsylla 

palmeni and C. phlebophylla developed from egg to adult within 36–41 days, an 

exceedingly tight phenological schedule (Hodkinson et al. 1979). Development rates 

of psyllid and host are, nevertheless, independently temperature-dependent. Later 

studies of C. palmeni, C. propinqua and C. brunneipennis along altitudinal transects in 

Norway showed that life cycle completion was determined by the available thermal 

budget and its differential effect on psyllid and host development rates (Hill et al. 

1995). Each psyllid had a wide distribution along the transect but failed to complete 

its life cycle at a characteristic upper altitudinal limit because host growth became 

too slow to support development or the psyllid developed too slowly to exploit the 

phenological window available. The upper limit for C. palmeni was, however, 

significantly higher than that for C. brunnepennis (Hill et al. 1995). Soluble nitrogen 

concentrations within catkins declined slightly with increasing altitude but the 

decline over time during catkin development at a given altitude was far steeper, 

implying a rapidly narrowing time window for psyllid development as catkins aged 

(Hill et al. 1998; Hodkinson et al. 2001). 

MacLean (1983) extended these ideas to propose a simple temperature-driven 

phenological model of psyllid and host-plant development on a wider geographical 

scale. The latitudinal distribution of nearly all Alaskan psyllid species is more 

restricted than that of their host plants (MacLean and Hodkinson 1980). The model 

demonstrates how a psyllid’s northern limit might be set by the failure of its host 

plant to develop and grow sufficiently quickly to support life cycle completion within 

one season. The southern limit, by contrast is determined by the plant developing too 

quickly to permit psyllid development through to maturity. Furthermore, psyllids



may, because of phenological contstraints, exploit different host plants in separate 

parts of their range or even exploit different tissues on the same host species. The 

Greenland willow psyllid Cacopsylla groenlandica, in the relatively benign climate of 

southern Greenland, reproduces on four different Salix species, developing on both 

catkins and growing shoot tips (Hodkinson 1997). Further northwards the thermal 

budget available for development decreases and the psyllid life cycle can be 

completed only on the catkins of one species, Salix glauca, despite other species often 

being present. 

Among temperate species that overwinter as larvae on evergreen plants, such as 

Strophingia ericae on Calluna and Asphagidella buxi on Buxus, phenological 

synchrony is probably less important: once diapause is broken: the psyllids simply 

recommence development as the host plant resumes growth in the spring 

(Hodkinson 1973b; Nguyen 1968). Consequently, by contrast with the aforementioned 

Salix-feeding species, S. ericae is less dependent on precise host synchrony 

and occupies the full altitudinal range of Calluna (Hodkinson et al. 1999). 

Several psyllids, particularly Craspedolepta species, feed and overwinter as larvae 

on perennial herbaceous plant species that die back each year and pass the winter 

with the perennating buds usually present as small rosettes at the soil surface 

(Hemicryptophytes) or on tubers (Geophytes). These plants, frequently associated 

with xerophytic conditions, often grow rapidly and flower early in the year, 

presenting a time-limited opportunity for psyllid exploitation. Overwintering sites of 

the associated psyllid larvae are usually at or below the soil surface on the rosette 

buds (Craspedolepta nervosa), on fine roots (C. nebulosa and C. subpunctata) orat 

the base of old woody stems (C. eas) (Wheeler 1994; Bird and Hodkinson 2005). In 

spring late instar larvae migrate to the rapidly growing shoot and quickly complete 

development. Larvae of the next generation then migrate back down to the 

overwintering site before entering a long larval diapause, usually before midsummer. 

Close phenological synchrony is thus maintained and long exposure to dry 

summer conditions avoided. 

Many species of psyllid in tropical and subtropical regions do not undergo an 

extended diapause and reproduction is continuous. However, many of their host 

species do not produce new shoots and leaves continuously but put out flushes of 

new growth in response to variations in ambient temperature and moisture 

availability. Flushing cycles may be irregular and non-synchronous within species 

and may vary over short geographical distances. Even within individual host plants 

there may be marked differences in leaf quality between sun and shade leaves. 

Diclidophlebia xuani on Ricinodendron, for example, tends to attain higher 

population density on unshaded leaf shoots whereas psyllid galls on Persea tend 

to be more numerous on shade leaves (Aléné et al. 2006; Leege 2006). This again 

presents synchrony problems in psyllids that need to seek out suitable tissues on 

flushing trees on which to complete their life cycle. 

The relationship between the flushing cycle of tree and shrub species and the 

breeding success of their associated psyllid species has been widely documented. 

Good examples include Diclidophlebia harrisoni on Triplochiton, two Phytolyma 

species on Milicia, Diaphorina citri and Trioza erytreae on Citrus, D. lycii on Lycium, 

Acizzia uncatoides on Albizzia, several Cardiaspina and Glycaspis species on 

Eucalyptus, Mesohomotoma tessmanni on Theobroma, Protyora and Diclidophlebia 

species on Argyrodendron, and Heteropsylla cubana on Leucaena (Moore 1961; Clark



1962; White 1967; Catling 1969a; Entwistle 1972; Osisanya 1974a, 1974b; Bigornia 

and Obana 1974; Clark and Dallwitz 1975; Leeper and Beardsley 1976; Lakra et al. 

1983; Cobbinah 1986; van den Berg and Villiers 1987; Rapisarda 1990a; Basset 

1991). Similar examples have also been observed in milder temperate regions 

including Ctenarytaina eucalypti on planted Eucalyptus in Europe and Trioza 

vitreoradiata on Pittosporum in New Zealand (Carter 1949; Purvis et al. 2002). 

In both the aforementioned set of species and those non-tropical multivoltine 

species with a winter diapause and several summer generations, such as Cacopsylla 

pyricola, successful host-plant usage depends on females correctly discerning the 

physiological state and condition of the host-plant tissue at the time of oviposition 

(White 1970a; Nguyen 1972b; Moran and Buchan 1975; Butt and Stuart 1986; Stuart 

et al. 1989; Horton 1990a, b; Horton and Krysan 1990, 1991; van den Berg, 

Anderson, et al. 1991; Mensah and Madden 1992a; Puterka et al. 1993; Luft and 

Paine 1997). Selection must favour young growing tissues rather than older mature 

leaves and shoots. For certain pest species, such as Cacopsylla pyricola on Pyrus, for 

which detailed information is available on the temperature dependence of diapause 

termination, pre-reproductive period, oviposition period and development rates, 

phenological models can be used to predict psyllid population growth characteristic 

and densities for the following summer period (Schaub et al. 2005). This can help 

determine when subsequent population control measures should be applied. 

Many species of psyllid persist within enclosed or roll-leaf galls on the mature 

leaves of their host throughout much of the year. Even in these species, however, the 

timing of oviposition and subsequent gall initiation, to correspond with the flushing 

cycle of new growth, is important (Raman 1994, 2003). Gall induction usually 

involves the active modification of growth in young rapidly growing plant tissue and 

plants are thus most susceptible to galling at time of flushing (Kumar et al. 1981). 

Subsequent growth of plant tissue through to maturity would normally correspond 

with a period of declining quality for psyllid feeding that is overcome by the 

metabolic changes induced within the leaf as a result of psyllid feeding that allow 

continued development within the gall. 

The close correspondence between new tissue growth and gall initiation, and 

increasing gall mortality on maturing leaves, has been observed in many psyllids 

representing several different families, including Pachypsylla species on Celtis, 

Phacopteron lentiginosum on Garuga, Schedotrioza and Glycaspis species on 

Eucalyptus, Trioza simplifica on Terminalia, Trioza gigantea on Vaccinium, 

Calophya spp and Tainarys sordida on Schinus and Baccharopelma baccaridis on 

Baccaris (Smith and Taylor 1953; Walton 1960; Kandasamy 1980; Kandasamy and 

Krishnan 1981; Taylor 1987; Espirito-Santo and Wilson Fernandez 1998, 2002; Saiz 

and Nunez 2000). In many of these species adult emergence from the gall is timed to 

correspond with a predictable seasonal flush of new growth and often involves a 

larval or adult diapause designed to maintain host-plant synchrony. 

A similar situation pertains in several leaf pit-gall forming species of Trioza 

including T. camphorae, T. cinnamomi, T. machilicola, T. obsoleta and T. ilicina in 

which oviposition occurs on new flush spring growth and larval diapause 

corresponds with summer/winter leaf maturity (Sorin 1959a; Miyatake 1968a,1969; 

Vaishampayan and Bahadur 1980; Rapisarda and Belcari 1999). Synchrony and 

survival may be further enhanced in species such as Pachypsylla venusta on Celtis 

and Trioza tabebuiae on Tabebuia in which the presence of galls prevents galled



leaves being shed during normal autumn abscission and thus remaining on the host 

tree (Smith and Taylor 1953; De Queiroz Santana and Burckhardt 2001). However, 

contrary to this trend, Celtis laevigata displays early abscission of leaves with 

Pachypsylla galls and this may serve as a plant defence mechanism (Stromgren and 

Lanciani 2001). Even in tropical tree species, including Milicia excelsa, staggered loss 

of leaves by adult trees allows small populations of associated psyllids (e.g. 

Phytolyma fusca) to survive as galls through the dry season when the majority of 

trees are leafless (White 1967). 

Development on different hosts 

The relative success of a psyllid species in completing its life history may vary 

significantly among different potential host species or even among different 

provenances within the same host species. Breeding success is determined by the 

initial attractiveness of a particular host, the extent to which oviposition occurs and 

the survival of these eggs through to adult emergence. 

In large-scale host-plant trials psyllids are often found to oviposit on a much 

wider range of plant species than those on which they can successfully complete 

development (Baloch and Ghaffar 1984). Prosopidopsylla flava, for example, 

oviposited on 57 of 58 host species (Leguminosae and Rosaceae) tested but 

developed successfully on just four species of Prosopis (Leguminosae) (van Klinken 

2000). Similarly, Boreioglycaspis melaleucae laid eggs on 27 out of 43 species of 

Myrtaceae but developed successfully on just two or three species of Melaleuca 

(Purcell et al. 1997; Wineriter et al. 2003). 

Different species of plant within a given host range often vary in their 

susceptibility to the associated psyllid species, ranging across a spectrum from highly 

susceptible to near resistant. Examples include Glycaspis brimblecombei on 

Eucalyptus spp, Ctenarytaina thysanura on Boronia spp Cacopsylla pyricola on 

Pyrus and Heteropsylla cubana on Leucaena spp (Williams et al. 1963; Westigard 

et al. 1970; Mensah and Madden 1991; Brennan, Hrusa, et al. 2001; Mullen and 

Shelton 2003; Pasqualini et al. 2006; Center et al. 2007). 

Similar variation in susceptibility also occurs across provenances, cultivars and 

varieties within single species of host plant, as in Phytolyma lata on Milicia excelsa, 

Acizzia melanocephala on Acacia nilotica, Cacopsylla pyricola and C. pyri on Pyrus 

communis, Heteropsylla cubana on Leucaena leucocephala and Bactericera cockerelli 

on Lycopersicon (Harris 1973; Chang and Philogene 1976; Butt et al. 1989; Cobbinah 

and Wagner 1995; Berrada et al. 1995; Baldassari et al. 1996; Puterka 1997; Mullen 

and Shelton 2003; Finlay-Doney and Walter 2005; Liu and Trumble 2006; 

Pasqualini et al. 2006; Palmer and Witt 2006). Such variation forms the basis for 

selective breeding for host-plant resistance against pest psyllid species or identifying 

varieties of invasive weed species susceptible to biological control (e.g. Nguyen and 

Messi 1973; Lahiri and Biswas 1980; Palmer and Witt 2006; Center et al. 2006). 

Sometimes the within-species variation in plant susceptibility may be as great or 

greater than the between-species variation. Asphagidella buxi, for instance, breeds 

naturally on Buxus sempervirens var arborescens but not on var rotundifolia, yet it 

breeds successfully on B. macrophylla (Nguyen 1965). Comparable apparent 

anomalies are found in the host range of Heteropsylla cubana (Mullen and Shelton 

2003). Differences in susceptibility may even occur among plants of the same



provenance. The most striking example occurs in species of Myrtaceae that display 

heteroblasty, strong morphological differentiation between juvenile and mature 

foliage related to tree age (Brennan, Weinbaum, et al. 2001). Ctenarytaina eucalypti, 

for example, oviposits and develops on juvenile shoots of Eucalyptus globulus 

whereas C. spatulata develops primarily on the mature foliage (Brennan and 

Weinbaum 2001a, 2001b, 2001c). 

Variation in psyllid development success among host species and cultivars can 

usually be explained by differences in the initial attractiveness of the foliage, 

differential oviposition rates, larval survival rates and larval development period. 

Diaphorina citri, when tested using four host Citrus species, developed most 

successfully on C. paradisi as a result of higher fecundity, faster development time 

in the final instar and higher larval survival (Tsai and Liu 2000; Nava et al. 

2007). Heteropsylla cubana developed more successfully on Leucaena leucocephala 

than on L. collinsii in which slower colonization resulted in 46–63% fewer eggs 

being laid, a 67% reduction in larval survival and the production of smaller, 

probably less fecund adults (Lapis and Borden 1993a, 1993b). The host preference 

hierarchy in Bactericera cockerelli on Lycopersicon is similarly based on rates of 

oviposition, development and survival, although these parameters may differ 

between native and invasive populations of the psyllid (Liu and Trumble 2004, 

2005, 2006, 2007). There are, however, apparently anomalous examples in which a host 

plant that is most attractive for oviposition is not the most suitable for larval 

development. Trioza erytreae, for example, oviposits preferentially on Citrus limon but 

the development period is shorter and the adult size attained is greater on indigenous 

Rutaceae such as Vepris and Clausena (Moran 1968a, 1968b). 

The precise mechanisms that determine the preference hierarchy of host plants 

appear to vary among psyllid species. In Cacopsylla pyricola, when offered three host 

plant species in the laboratory, host acceptance for oviposition appeared determined 

by interactions among plant species, female egg load and the time for which the 

psyllid was deprived of a suitable host (Horton and Krysan 1991). Cues received 

during probing and settling released oviposition but egg laying ceased earlier on 

lower hierarchy species, suggesting that further cues received during oviposition were 

also involved in prolonging egg laying. 

Other factors implicated in establishing preferences include host species 

phenology (Euphyllura phillyreae), amount of glaucous wax on the leaf surface 

(Glycaspis brimblecombei), physical hardness of the terminal shoot (Ctenarytaina 

thysanura), leaf colour (Mesohomotoma tessmanni and G. brimblecombei), the 

presence of attractive chemicals such as caryophyllene (Heteropsylla cubana) and low 

concentrations of repellent chemicals such as phenolics (Cacopsylla pyricola), 

terpenoids (Boreioglycaspsis melaleucae) or glucosinolates (undescribed ‘‘Aphalara’’ 

sp.) (Moran and Brown 1973; Louda and Rodman 1983; Messi 1983a; Ullman and 

McLean 1988a; Mensah and Madden 1991; Luft and Paine 1998; Luft et al. 2001; 

Brennan and Weinbaum 2001a, 2001c, 2001d; Finlay-Doney and Walter 2005; 

Wheeler and Ordung 2005; Prophetou 1997). In Bactericera cockerelli on 

Lysopersicon jumping and leaf avoidance behaviour was greatest on the most 

resistant cultivars, suggesting active repellence and not just an antixenosis response 

(Liu and Trumble 2004). A single gene (Mi-1.2) from wild tomato, Solanum 

peruvianum, confers resistance to B. cockerelli in some commercial tomato varieties 

(Casteel et al. 2007).



Host-plant amelioration, disease transmission and endosymbionts 

Host plants, particularly when leaves are mature, provide a low quality source of 

soluble nutrients, especially available nitrogen in the form of amino acids, for sapfeeding 

psyllids. This frequently results, as noted earlier, in lower rates of 

reproduction, slower development and reduced longevity on mature versus young 

or senescing foliage (Nguyen 1972b). Psyllids, however, often display mechanisms 

through which they enhance, ameliorate or partly circumvent the condition of their 

mature host plant for larval growth and development (White 1970b). 

Feeding involves the injection of saliva and its associated enzymes, such as 

amylase, into the host, most frequently into the phloem and its associated tissues or 

into leaf mesophyll (Pussard 1939; Williams and Benson 1966). This may or may not 

result in wider salivary translocation within the plant. Species of Cardiaspina, 

Glycaspis, Creiis and Lasiopsylla on Eucalyptus blakeleyi and E. melliodora induce 

localized symptoms of varying severity in phloem tissues that resemble premature 

senescence (Woodburn and Lewis 1973). In mesophyll-feeding species such as 

Cardiaspina retator on Eucalyptus camaldulensis feeding similarly produces cell 

degeneration that resembles senescence and involves the mobilization of lipids, 

amino acids and soluble proteins (Crawford and Wilkens 1996). 

Some psyllids, including known pest species such as Trioza apicalis (on carrot) 

and Bactericera cockerelli (on potato and tomato), induce a wider systemic 

phytotoxaemia within their host, resulting in severe growth distortion, cellular 

necrosis and yellowing of leaves (Richards and Blood 1933; Eyer and Crawford 

1933; Eyer 1937; Sanford 1952; Laska 1964; Markkula and Laurema 1971), which 

again resemble senescence, with the associated mobilization of soluble nitrogen and 

increasing the availability of nutrients to the psyllid (Laurema 1989). This may, as in 

T. apicalis, be accompanied by an increase in leaf monoterpenes concentrations and 

result in reduced root growth (Nissinen et al. 2005, 2007). It may also be associated 

with the transmission of plant diseases, particularly mycoplasmas (see next section). 

Gall formation, which is largely outside the scope of this review, similarly brings 

about improvements in host tissue quality for feeding psyllid larvae through the 

creation of metabolic sinks within the plant tissue (e.g.Raman 1987; Rajadurai 

et al.1990; Mani and Raman 1994; Yang et al. 2006). 

Enhanced amelioration may occur when psyllids feed in groups rather than 

singly. Cacopsylla pyri on Pyrus communis and Cardiaspina densitexta on Eucalyptus 

fasciculosa, for example, showed higher reproduction, greater longevity or enhanced 

survival with increasing feeding group density up to an optimum (White 1970b; 

Nguyen 1971). Galls of Pachypsylla celtidismamma on Celtis similarly grew larger 

when more than one gall was present per leaf (Heard and Buchanan 1998). However, 

feeding by some species at high densities, such as Boreioglycaspis melaleucae on 

Melaleuca may promote increased leaf abscision and a decline in host quality 

(Morath et al. 2006). Similarly, feeding-induced changes in the concentrations of leaf 

nutrients, chlorophyll, minerals and phenolics may lead to an ultimate reduction in 

food quality for Cacopsylla species on Pyrus (Scutareanu and Loxdale 2006). 

Significance of disease transmission 

Several psyllids are known vectors of plant diseases and as such are regarded as 

noxious pests. However, psyllids often show close association with these pathogens.



When viewed from the psyllids’ perspective, the association may prove highly 

beneficial by bringing about pathogen-induced changes in the host plant that makes 

it more acceptable or more nutritious for psyllid development (Weintraub and 

Beanland 2006). Pathogens may, for example, induce physiological changes 

resembling the premature senescence noted previously or produce reduced levels 

of defensive chemicals. However, our knowledge of these psyllid–pathogen 

relationships is confined to just a few crop plants but similar pathogens occur 

widely in wild hosts where the insect–vector relationships remain to be established 

(Weintraub and Beanland 2006). 

The main plant diseases associated with and transmitted by psyllids (Table 2) are 

viruses, and bacteria within three main groups, the liberibacters, the phytoplasmas 

(previously known as mycoplasma-type organisms) and fireblight. Several of the 

causative agents are taxonomically poorly defined, being identified solely from their 

RNA, and are included in the Candidatus category of the bacterial classification. The 

disease organisms are initially ingested during psyllid feeding and are then later reinjected 

back into other plants with the psyllid saliva. Phytoplasmas and 

liberibacters in particular are restricted to the phloem sieve tubes and circulate with 

the plant sap, making them ideal candidates for transmission by psyllids. Within the 

insect they cross the gut wall, multiply in the haemolymph and migrate into the 

salivary glands ready for onward transmission in the saliva (Hibino et al. 1971; Chen 

et al. 1973; Cousin and Boudon-Padieu 2002; Hung et al. 2004; Weintraub and 

Beanland 2006). 

Both larvae and adults appear capable of transmitting phytoplasmas (Carraro, 

Loi, et al. 1998; Tedeschi and Alma 2004). Some evidence exists for transovariole 

transfer of these bacteria between female psyllids and their offspring in psyllids such 

as for Phytoplasma prunorum in Cacopsylla pruni (Tedeschi et al. 2006). However, 

Liberibacter asiaticum in Diaphorina citri and Phytoplasma mali in Cacopylla 

melanoneura, by contrast, do not appear to be vertically transmitted between 

generations (Hung et al. 2004; Tedeschi et al. 2006). Interestingly, infection of potato 

by a virus provides cross-protection against psyllid yellows phytoplasma transmitted 

by Bactericera cockerelli (Staples 1968). 

Psyllids may also benefit from a general weakening of the plant caused by sooty 

moulds growing on the larval excreta or honeydew deposited on the leaf or shoot 

surface. Examples include Cacopsylla pyricola on Pyrus and Ctenarytaina thysanura 

on Boronia (Savinelli and Tetrault 1984; Mensah and Madden 1992b). 

Significance of endosymbionts 

Endosymbiotic bacteria also play a more direct role in the nutrition of psyllids, 

which in common with aphids, whiteflies and pseudococcids, support such bacteria 

within, or associated with, specialized cells (bacteriocytes) that aggregate to form a 

bacteriome within the insect’s body cavity (Tarsia in Curia 1934; Chang and 

Musgrave 1969; Waku and Endo 1987; Fukatsu and Nikoh 1998; Thao et al. 2000a). 

Phloem sap, on which many psyllids feed, is rich in sugars but poor in amino acids 

and it is thought that the endosymbionts synthesize essential amino acids and 

vitamins such as riboflavin that then become available to the psyllid (Thao et al. 

2000a; Thao et al. 2001).

Table 2. List of plant diseases transmitted by psyllid vectors. 


Organism Disease Psyllid vector Reference 

Bacteria 

Candidatus status 

Liberibacter asiaticus Citrus Huanglongbing 

Diaphorina citri Halbert and Manjunath (2004), Davis et al. (2005), 

(in Asia and Florida) (HLB)5Greening Disease 

Das et al. (2007) 

Liberibacter africanus Citrus Huanglongbing 

Trioza erytreae Van den Berg et al. (1987), Anon. (1988) 

(in Africa) 

(HLB)5Greening Disease 

Liberibacter americanus Citrus Huanglongbing 

Diaphorina citri Teixeira et al. (2005) 

(in S. America) 

(HLB)5Greening Disease 

Phytoplasma Peach Yellow Leaf Roll (PYLR) Cacopsylla pyricola Purcell and Suslow (1984), Blomquist and Kirkpatrick 

(2002) 

Phytoplasma prunorum European Stone Fruit Yellows Cacopsylla pruni Carraro, Osler, et al. (1998), Jarausch et al. (2001), 

(ESFY)5Apricot Chlorotic 

Carraro et al. (2004), Labonne and Lichou (2004), 

Leafroll 

Delic et al. (2005) 

Phytoplasma mali Apple Proliferation (AP) Cacopsylla picta Frisinghelli et al. (2000), Jarausch et al. (2003), 

C. melanoneura 

Tedeschi et al. (2002), Tedeschi and Alma (2004) 

Phytoplasma pyri (in Pear Decline (PD) Cacopsylla pyricola Jensen et al. (1964), Ullman and MacLean (1988b), 

Europe and N.America) 

C. pyri 

Davies et al. (1992), Giunchedi et al. (1994), 

Carraro et al. (1998), Ben Khalifa et al. (2007) 

Phytoplasma (in Taiwan) Pear Decline (PDTW) Cacopsylla qianli Liu et al. (2007) 

C. chinensis 

Phytoplasma Carrot Stolbur Bactericera trigonica Font et al. (1999), Weintraub and Beanland (2006) 

Léclant et al. (1974) (misidentification as B. 

nigricornis?) 

‘Rickettsia type organism’ 

Wissadula Proliferation (WP) Paracarsidara dugesii (Löw) Dabek (1983) (as concolor) 

Family 

Enterobacteriaceae 

Erwinia amylovora Fireblight of orchard trees Cacopsylla pyricola Wilde et al. (1971), Hildebrand et al. (2000) 

Psyllids generally 

Virus 

(SB26/29) Potato Rugose Stunting Virus Russelliana solanicola Tenorio et al. (2003) 

Undetermined 

Zebra chip disease Bactericera cockerelli Munyaneza et al. (2007) 

Downloaded By: [University of Florida] At: 15:14 17 August 2010



The psyllid endosymbionts fall into two main groups, primary (P) and secondary 

(S). The P endosymbionts, found within the bacteriocytes, are genetically similar 

throughout the psyllids, suggesting that they have colonized the psyllids just once, 

and then co-evolved with their hosts (Thao et al. 2000b). They are defined as a single 

taxon Candidatus Carsonella ruddii (Thao et al. 2001; Spaulding and von Dohlen 

2001). The S endosymbionts, by contrast, are present in cells associated with the 

bacteriocytes and appear to be multiply derived, consisting of several distinct groups 

within the Eubacteriaceae (Spaulding and von Dohlen 1998; Thao et al. 2001; 

Fukatsu and Nikoh 1998). Their function in psyllid nutrition is less clear than for the 

P endosymbionts (Thao et al. 2001). Secondary endosymbiont infection levels may 

vary greatly among populations, as in Glycaspis brimblecombei, where infection 

appears more associated with levels of parasitism than with nutrition (Hansen et al. 

2007). 

Dispersal 

Effective dispersal is a key element in the life history of psyllids irrespective of the 

habitat within which they are found. In insects that are capable of flying only limited 

distances under their own power, it serves several important purposes. In particular, 

it enables a species to track the changing spatial distribution of its host plant and/or 

the temporal availability of the food resource that it relies on for breeding success. It 

allows psyllids to move between different host-plant species and to exploit non-hostplant 

species as overwintering sites and it permits species to escape the effects of 

strong intraspecific competition and natural enemies. Among economically 

important species, such as Trioza erytreae, it expedites rapid colonization of 

cultivated Citrus hosts (metapopulation sinks) by psyllids originating on indigenous 

host plants within the surrounding area (metapopulation sources) (van den Berg, 

Deacon and Steenekamp 1991). 

Dispersal distance 

There is strong evidence to suggest that, as a group, the psyllids are highly effective 

dispersers over both short and long distances, although in almost all cases dispersal 

is wind assisted. Dispersing psyllids belonging to the genera Cardiaspina, 

Ctenarytaina, Eucalyptolyma, Psylla sensu lato and Bactericera have been taken in 

drogue nets towed behind light aircraft in Australia, the Galapagos Islands and the 

USA or in kite mounted nets in the Canary Islands (Glick 1939; White 1970a, 1973; 

Ashmole and Ashmole 1988; Peck 1994). Psyllids form a major component of the 

insect flotsom found on the surface of the sea at sites around the UK coastline and 

off the west coast of the USA (Cheng and Birch 1978; Hardy and Cheng 1986). 

Species belonging to several genera including Aphalara, Craspedolepta, Livia, 

Cacopsylla, Euphalerus sensu lato, Acizzia, Bactericera and Trioza are a common 

component of aerial deposition on high altitude snowfields in California and 

Tenerife (Papp and Johnson 1979) or early successional volcanic areas in the Azores 

(Ashmole et al. 1996). Thirty-seven species have been recorded as vagrants in yellow 

water traps in northern Italy and several, including Cacopsylla melanoneura, C. 

affinis, Bactericera albiventris and Trioza urticae, overwinter on Pinus in northern 

England at a distance of around 13km from the nearest host plant (Hodkinson 1972,



1983c). Trioza apicalis similarly moves up to 1km on to its overwintering shelter 

plants (Kristoffersen and Anderbrant 2007). 

Tropical forest species may also move considerable distances. The coastal 

mangrove-feeding Limbopsylla lagunculariae has been taken inland in central 

Panama, many kilometres from the coast (Brown and Hodkinson 1988). 

Populations of Boreioglycaspis melaleucae, newly introduced for the biological 

control of Melaeuca, spread at a rate of up to 10km per year. Further testimony to 

the rapid dispersal powers of psyllids is the time (,10 years) in which Heteropsylla 

cubana spread from an origin in Central America to colonize virgin plantings of its 

forage legume host Leucaenca leucocephala in the Pacific, Asia, Australia and Africa 

(Hodkinson 1988b). 

Experimental studies suggest that in species such as Arytainilla spartiophila, 

Acizzia russelli and Trioza erytreae females disperse further than males, as evidenced 

by an increase in the female: male sex ratio with increasing distance, 90–1500m 

depending on species, from the source (Dempster 1968; Webb 1977; van den Berg 

and Deacon 1988). However, this would be an ineffectual strategy in species with a 

post-dispersal ovarian diapause. For psyllids living on short herbaceous plants, such 

as Trioza urticae, the effective dispersal boundary layer, within which most directed 

dispersal movements take place, is probably less than 1m (Omole 1980). It is the 

individuals that stray above this height that are more likely to be wind dispersed. 

Adaptive significance of dispersal 

Multivoltine psyllids often show differences in dispersal behaviour among 

generations. Summer and autumn emerging adults of Cardiaspina densitexta in 

Australia, for example tend to show what White (1970c) calls ‘‘concentrative’’ 

behaviour. Adults blown out of a given Eucalyptus tree usually fly back into the 

same tree, and appear to neglect adjacent trees with significantly lower populations. 

This results in some trees supporting high psyllid densities while other nearby trees 

have low-density populations. By contrast, long-distance ‘‘dispersive’’ behaviour is a 

characteristic feature of the spring generation that has developed at shorter day 

length and lower temperatures. This parallels certain multivoltine north temperate 

species, such as Cacopsylla pyricola in which the winter morph, with its relatively 

longer wings produced under short day length, shows significantly greater dispersive 

behaviour than the spring or summer generation (Hodgson and Mustafa 1984; 

Horton, Burts, et al. 1994). The actual duration of the flight activity period is similar 

in the two morphs but flight frequency is much greater in the former (Horton and 

Lewis 1996). The actual rate of dispersal of these winter forms out of pear orchards 

tends to be correlated with the rate of leaf fall, lower temperature and density (Fye 

1983; Horton, Burts, et al. 1994). 

Univoltine species moving onto overwintering shelter plants, by comparison, 

exhibit both an autumn and a spring period of peak dispersal as they move to and 

from their winter host. Where significant dispersal occurs in summer generations, as 

in Arytainilla spartiophila, Acizzia russellae and Trioza erytreae it is usually 

associated with interspecific competition arising from high populations and declining 

host-plant favourability or increasing pressure from natural enemies (Dempster 

1968; Webb 1977; van den Berg, Anderson, et al. 1991). Psyllids disperse to new, 

more favourable plants.



Dispersal opens up the opportunity for host-plant alternation in multivoltine 

psyllids but this behaviour, so typical of many aphid species, is rare in psyllids, with 

just two known examples. Bactericera crithmi on Malta undergoes a winter 

generation on Ferula during the period when its normal host Crithmum is dormant 

(Mifsud 1997). It moves back to Crithmum in spring. Similarly, the vector of psyllid 

yellows disease of potato, Bactericera cockerelli overwinters as source populations 

on Lycium and other wild Solanaceae in the warmer southern USA. In spring there is 

a general northwards wind-assisted dispersal of adults to establish sink populations 

breeding on potato (Solanum) in regions far to the north (Knowlton 1933; Knowlton 

and Thomas 1934; Swenk and Tate 1940; Wallis 1946, 1955). 

Dispersal allows psyllids to track spatial and temporal changes in the availability 

of host-plant tissues suitable for growth and development. Many psyllids require 

flushes of young, rapidly growing leaf tissues on which to breed. As these leaves 

mature they become unsuitable for psyllid development and the psyllid must seek out 

new breeding sites. This is most acute where individuals of particular tree species drop 

leaves completely but asynchronously. In some Australian species, such as Cardiaspina 

densitexta and C. albitextura, this can result in progressive waves of psyllid outbreak 

and decline spreading across the landscape as psyllids track the flushing pattern of 

their host Eucalyptus (Morgan 1984). This precludes the need for diapausing stages. 

The problem may be particularly acute for tropical rainforest psyllids where individual 

host plants are usually sparsely distributed within a highly species diverse tree 

community and often flush asynchronously. A high level of dispersive behaviour by 

psyllids is necessary constantly to track the spatial and temporal availability of their 

food resource (Brown and Hodkinson 1988; Hodkinson and Casson 2000). 

Even in temperate regions individual host plants may vary markedly in 

suitability between successive years. Many species of Rosaceae, for example, exhibit 

biennial or irregular patterns of flowering by individual plants that may affect their 

suitability as psyllid hosts (Sutton 1984). It is unsurprising, therefore, that highly 

dispersive psyllids like Cacopsylla melanoneura and C. affinis are associated with one 

such rosaceous plant species, namely Crataegus (Sutton 1984). 

Overwintering on shelter plants 

Many temperate species of psyllids are known to disperse to, and overwinter as 

adults on, evergreen shelter plants before moving back onto their true host in the 

spring (Reuter 1909; McAtee 1915; Hodkinson 1972; Ha˚gvar and Ha˚gvar 1975; 

Kristoffersen and Anderbrandt 2007) (Table 1). Such hosts are usually conifers, 

primarily species of Pinus, Picea, Abies, Taxus, Tsuga, Cupressus and Juniperus but 

may also include thorny evergreen shrubs such as Ulex. InTrioza apicalis there 

appears to be a distinct order of preference, with Picea supporting higher 

populations than Pinus or Juniperus (Kristoffersen and Anderbrandt 2007). The 

period spent on shelter plants, which usually matches periods when the host is 

dormant or unfavourable for psyllid development, is normally accompanied by an 

ovarian diapause. This adaptive overwintering strategy is found in almost all 

temperate psyllid families but is most frequent among species of Aphalara, Livia, 

Cacopsylla, Bactericera, Phylloplecta and Trioza. It is, however, recorded more 

sporadically in a wider range of genera including Pachypsylla, Calophya, 

Camarotoscena, Togepsylla, Ligustrinia, Cyamophila, Livilla and Epitrioza (Table 1).



Psyllids on conifers are easily caught and observed whereas those overwintering 

in leaf litter or grass tussocks are much less obvious. Careful studies on some species 

such as Bactericera perrisi, Aphalara avicularis, A. exilis and A. longicaudata show 

that individuals overwinter both on conifers and in litter, perhaps raising the 

question for other species of what actual proportion of the overwintering population 

is on conifers (Lauterer 1976, 1982, 1991). Furthermore, several species of Aphalara, 

Cacopsylla and Trioza, known to overwinter on conifers, can also be overwintered 

successfully in grass tussocks maintained in pots (Heslop-Harrison 1937). These 

individuals tend to be much lighter coloured than those spending winter on conifers 

(Heslop-Harrison, 1937). 

One question that has not been fully answered is whether overwintering psyllids 

feed on conifers or other shelter plants. Experiments in our laboratory using Pinus 

shoots labelled with C14 and P32 repeatedly failed to provide definitive evidence for 

winter feeding by Cacopsylla melanoneura, although the maintenance of body 

condition and levels of hydration suggest that some feeding must take place (Jackson 

et al. 1990). There is, however, some evidence that overwintering Cacopsylla pyricola 

may feed on transitory hosts such as Prunus persica (Ullman and McLean 1988b). 

Mate finding and aggregation on host plants 

Small dispersive insects, such as psyllids, are faced with the problem of finding 

suitable mates, either on their breeding or overwintering host plants. Species are 

frequently found as highly-aggregated, mixed-sex colonies on the tissues of their 

host. Several are known to emit species- and gender-specific stridulation calls or to 

make drumming sound or vibrations with their tarsi on leaf surfaces (Campbell 1964; 

Ossiannilsson 1950; Heslop-Harrison 1961; KL Taylor 1985; Carver 1987; 

Tishechkin 1989, 2005, 2007; Percy et al. 2006), which are thought to aid mate 

location and aggregation. There is also some evidence for chemical mechanisms 

leading to aggregation and mate finding. Male Cacopsylla pyricola are attracted to 

volatile chemicals emanating from pear shoots with receptive post-diapause females 

present or from shoots that have recently supported populations of such females. 

The precise nature of the chemical stimulus is unknown and it remains to be 

determined whether the chemicals involved originate from the psyllid, the host plant, 

or a combination of both (Horton et al. 2007; Horton and Landolt 2007). However, 

in some other species, such as Cardiaspina albitextura, host-plant tissues previously 

occupied by psyllids appear less favourable for oviposition than formerly 

unfrequented sites (Clark 1962, 1963b). 

Variation in fecundity among species 

It might be predicted that the fecundity of psyllid species is related to their type of 

life cycle, with species having larvae living in protective galls or lerps producing 

fewer eggs than those living on exposed growing tips. There is, however, surprisingly 

little pattern in the fecundity of psyllid species (Table 3). Experimentally measured 

fecundity differs widely, even among species within the same genus or family. Where 

repeated measures have been made on the same species in different localities or at 

different times, such as in Trioza erytreae, Heteropsylla cubana or Diaphorina citri, 

mean fecundity may differ by a factor of two or more (Table 3). Furthermore, there 

is little to suggest major differences in fecundity related to taxonomic position.



Table 3. Fecundity of selected psyllid species on preferred host, illustrating variation in 

potential reproductive output across the group. Numbers given are mean and maximum egg 

production per female under non-limited experimental conditions. 

Family Species Maximum Mean Reference 

Psyllidae Aphalara 

c. 300 Lauterer (1982) 

polygoni 

(as rumicicola) 

Paurocephala 

psylloptera 

640 { 

Hsieh and Chen (1977) 

Diclidophlebia 

eastopi 

502 Osisanya (1974a) 


harrisoni 

131 Osisanya (1974a) 


xuani 

532–758 Aléné et al. (2005a) 

Ctenarytaina 

86–92 Mensah and Madden 

thysanura 

(1992a, 1993b) 

Agonoscena 

893–1087 Mehrnejad and Copland 

pistaceae 

(2005) 

Gyropsylla 

spegazziniana 

180 108* Leite and Zanol (2001) 

Diaphorina citri 807 630 { 

Hussain and Nath (1927) 

Diaphorina citri 748 Liu and Tsai (2000) 

Diaphorina citri 858 Tsai and Liu (2000) 

Diaphorina citri 700 266 Mangat (1966) 

Diaphorina citri 520 210–300 Pande (1971) 

Cacopsylla 

melanoneura 

116 84 Domenichini (1967) 

Cacopsylla 

pyricola 

664 Burts and Fischer (1967) 

Cacopsylla 

pyricola 

445 McMullen and Jong (1977) 

Cacopsylla 

pyricola 

665 Rasmy and MacPhee (1970) 

Cacopsylla 

pyricola 

387–486 An et al. (1996) 

Cacopsylla pyri 47–406 Kapatos and Stratopoulou 

(1996) 

Cacopsylla pyri 2527 Lyoussoufi et al. (1988) 

Cacopsylla pyri 471 Nguyen (1970a) 

Cacopsylla pyri 588 Nguyen (1973) 

Acizzia 

uncatoides 

463 { 

Koehler et al. (1966) 

Acizzia 

986 Madubuny and Koehler 

uncatoides 

(1974) 

Arytaina genistae 962 435 Watmough (1968a) 

Arytainilla 

spartiophila 

354 93 Watmough (1968a) 

Heteropsylla 

cubana 

758 Patil et al. (1994)




Family Species Maximum Mean Reference 

Heteropsylla 

cubana 

857 394 Takara et al. (1990) 

Heteropsylla 

texana 

100 Donnelly (2002) 

‘Psylla’ isitis 828 479 { 

Grove and Gosh (1914) 

Spondyliaspididae Euphalerus 

clitoriae 

1148 Junior et al. (2005) 

Cardiaspina 

albitextura 

220 124* Clark (1962, 1963b) 

Cardiaspina 

albitextura 

290 45 Morgan and Taylor (1988) 

Boreioglycaspis 

melaleucae 

78 Purcell et al. (1997) 

Calophyidae Apsylla cistellata 141–150 Monobrullah et al. (1998) 

Apsylla cistellata 141 Prasad (1957) 

Carsidaridae Carsidara limbata 1701 Ding et al. (1987) 

Allocarsidara 

malayensis 

50 Gadug and Hussein (1987) 

Mesohomotoma 61 48 

tessmanni 

{ 

Igboekwe and Adenuga 

(1983) 

Triozidae Phylloplecta 

tripunctata 

202 94–164 Petersen (1923) 

Trioza erytreae 560 327 Moran and Blowers (1967) 

Trioza erytreae 787 Van den Berg, Deacon and 

Thomas (1991a) 

Trioza erytreae 827 Van den Berg (1990) 

Trioza eugeniae 331 198 Young (2003) 

Trioza hirsuta 180 99 Dhiman and Singh (2004) 

Trioza 

magnicauda 

692 Chang et al. (1995) 

Bactericera 

cockerelli 

1176 439 Pletsch (1947) 

Bactericera 

cockerelli 

1300 318 Knowlton and Janes (1931) 

Bactericera 

tremblayi 

803 431 Tremblay (1965b) 

Schedotrioza 

multitudinea 

487 GS Taylor (1985, 1987) 

Trichochermes 

walkeri 

279 201 McLean (1998) 

Neotrioza 

taveresi 

219 Butignol and Pedrosa (2003) 

Pauropsylla 

depressa 

.150 Abbas (1967) 

Note: occasionally, where means were not calculated in the original paper, they are calculated 

as (minimum+maximum)/2 (indicated by*); alternatively, some means (indicated by { ) are 

calculated directly from raw data given in the original paper; a range of values indicates 

recorded differences in means among seasons.



Typically mean fecundity per female ranges from 40–50 to over 1000, with a majority 

of species lying within the range 200–800. Lowest values (40–50) occur in some but 

not all Spondyliaspididae and Carsidaridae but highest values are often found in pest 

species of Psyllidae and Triozidae such as Agonoscena pistaciae, Trioza erytreae and 

Bactericera cockerelli in which some individual females produce up to 1300 eggs. 

Oviposition usually occurs over an extended period with females often maturing 

successive batches of eggs (An et al. 1996; Dhiman and Singh 2004). In species such 

as Cacopsylla pyricola, Trioza erytreae and Agonoscena pistaciae, repeated mating is 

necessary for a female to produce a full egg complement (Burts and Fischer 1967; 

van den Berg, Deacon and Thomas 1991a; Mehrnejad 1998; Mehrnejad and 

Copland 2006a), emphasizing the importance of continuous mate finding for 

successful life cycle completion. 

Factors influencing fecundity 

Several factors influence fecundity, including temperature, day-length and season, 

host condition and crowding. Fecundity, as noted earlier, tends to decline above and 

below an optimum temperature, as in Acizzia uncatoides, Agonoscena pistaciae, 

Cacopsylla pyri and Bactericera cockerelli (List 1939a; Madubunyi and Koehler 

1974; Nguyen 1970a; Mehrnejad and Copland 2006a). In multivoltine species such as 

Agonoscena pistaciae, Diclidophlebia xuani, Cacopsylla pyri, Cacopsylla pyricola egg 

output per female also varies significantly between seasons, with day length as well as 

temperature often an important determining factor (Nguyen 1970a; Kapatos and 

Stratapoulou 1996; Mehrnejad and Copland 2005; Aléné et al. 2005b). Moderate 

crowding initially enhances fecundity in species such as Trichochermes walkeri, 

Cardiaspina albitextura, Cacopsylla pyri and Arytaina genistae but increasing density 

beyond the optimum leads to declining fecundity (Watmough 1968a, 1968b; Clark 

1963a; Nguyen 1971, 1973; McLean 1998). The presence of eggs also acts as a 

deterrent to oviposition in Trioza eugeniae (Luft and Paine 1997). 

The previous discussion of life history parameters shows that psyllid species exhibit 

considerable variation in their life history characteristics and their adaptive response 

to their environment. It is now appropriate to examine the distribution of 

characteristics across the Psylloidea and to identify how the life cycle parameters 

are combined within the life histories of species both within and among higher taxa. 

Analysis of psyllid life history characteristics 

Table 1 shows the detailed life history characteristics of 342 psyllid species culled 

from the literature. Species are arranged in descending taxonomic sequence by 

family, tribe and genus. The key references from which data are drawn are listed. In 

the large genus Cacopsylla the Salix-feeding species with similar life histories are 

separated from the other species, which themselves are split into subgenera. 

Information is provided for each species on the major climatic zone within which it is 

found, the functional growth form of its host plant, the overwintering stage(s), the 

overwintering site, either on or off the host, voltinism, feeding site on the host and 

whether or not the larva forms galls of a particular type or lerps on the host plant. A 

full explanation of the various life history categories and their abbreviations as used 

in this table are listed in the note of Table 1.



Methods of coding and analysis 

The categorical life history data in Table 1 were numerically coded as the basis for a 

full analysis of the dataset, with each category of each characteristic given a separate 

numerical code. Voltinism presented a slight problem of coding and species were 

coded as semivoltine, univoltine or multivoltine, depending on the maximum life 

history duration. Taxonomic status of the psyllids was coded at the family, tribe and 

genus level. The basic objective of the analyses was to test whether there were 

recognisable and consistent patterns in the data linking particular life history traits 

with specific psyllid groups. 

Three separate multivariate analyses were employed to explore the structure of 

the dataset using the MINITAB 14 statistical package, namely Multiple 

Correspondence Analysis (MCA), Linear Discriminant Analysis (LDA), and 

Cluster Analysis (CA) of both the descriptive variables and of the species. 

MCA attempted to measure the extent to which different characters correspond 

with each other across the dataset and whether particular sets of characteristics 

correspond to particular taxonomic groupings within the psyllids. Analyses were 

initially conducted using life history characters alone to explore relationships among 

these variables and then repeated with psyllid groupings added. These analyses used 

the full dataset for all species. 

LDA tests whether suggested groupings of species are justified on the basis of the 

measured life history variables. This analysis was conducted three times using genus, 

tribe and family as the suggested species grouping. The output displays how many 

species are correctly or incorrectly allocated objectively to the proposed grouping. A 

high level of correct prediction indicates that life history characteristics tend to be 

relatively uniform within the group and are good predictors of taxonomic position. 

A low level suggests that life history characteristics are highly variable within 

proposed groups and thus poor predictors. This may, however, indicate greater 

adaptive flexibility as species have evolved differing life cycles to exploit varying 

opportunities within different environments. In conducting these analyses it is 

necessary to remove monobasic genera and tribes from the dataset, where necessary, 

as a single taxon cannot form a group. 

CA measured similarity among taxa or among variables within the main dataset 

using Euclidean distance: clustering was by average linkage. 

Results of analyses 

CA of variables (Figure 1) indicates two major groupings of characters and two 

outliers. The first grouping links voltinism and overwintering stage, not unexpectedly, 

to climate. The second links feeding site and overwintering site to plant 

functional type. The two outlying characters are gall type and lerp formation. Their 

separation from other characters appears to lie in the fact that lerp formation is 

largely concentrated within one family, the Spondyliaspididae, while gall instigation/ 

type is spread broadly but rather haphazardly across taxa. 

Overall, the level of correspondence among characters in MCA (Table 4) was 

low, with cumulative correspondence across species along the first five axes totalling 

only 26%. Introducing psyllid tribe as an additional character actually reduced 

correspondence further (19%). Gall and lerp formation were again the main outlying 

characters.



Figure 1. Dendrogram illustrating the level of correspondence among life history parameters 

measured across psyllid species. Note: similarity is measured by Euclidean distance; clustering 

is by average linkage. 

The total percentage of species allocated to the correct tribe by LCA was 

generally around a weighted mean of 47% (Table 5) but this hid wider variation 

among taxa, with one large group the Triozini in particular, dragging the total down 

but with other smaller tribes, such as Acizziini, Gyropsyllini, Mastigimatini and 

Phytolymini, showing good predictability. However, the correlation between group 

size and predictability (%) was non-significant (r50.01, p.0.05). Despite wide 

variability among taxa, predictability increased stepwise from the genus (n5302, 

40% correct) to the family level (n5322, 50% correct). This suggests that 

differentiation and thus discrimination among taxa, related to life history traits, 

increases with taxonomic level. 

Discussion and conclusions 

Within the Psylloidea there is considerable variation in the body form of the larvae 

related to phylogeny and one might predict that particular physiognomies are best 

Table 4. Results of multiple correspondence analysis across species showing percentage of 

cumulative correspondence explained by the first five axes. 

Cumulative Variation (%) 

Character set 1 2 3 4 5 

Excluding tribe 7 13 17 22 26 

Including tribe 5 9 12 16 19 

Note: analyses are presented both with and without the inclusion of psyllid tribe as a 

character. 

Axis



Table 5. Percentage of species allocated to their correct tribe using linear discriminant analysis 

based on life history characteristics. n is the number of species on which the percentage is 

based. 

n % correct 

Acizzini 3 100 

Aphalarini 27 67 

Arytainini 25 16 

Calophyini 7 43 

Ciriacremini 3 0 

Ctenarytainini 4 25 

Diaphorinini 3 33 

Diclidophlebiini 7 100 

Euphalerini 4 0 

Euphyllurini 6 17 

Gyropsyllini 2 100 

Liviini 4 75 

Mastigimatini 2 100 

Mesohomotomini 2 50 

Pachypsyllini 8 13 

Pachypsylloidini 11 100 

Paurocephalini 3 66 

Pauropsyllini 6 33 

Phytolymini 2 100 

Psyllini 72 68 

Psyllopseini 9 89 

Rhinocolini 6 33 

Spondyliaspidini 11 91 

Strophingiini 2 100 

Triozini 86 16 

Total 315 47 

adapted to exploiting plants in different ways (Loginova 1982; White and 

Hodkinson 1985). Thus, for example, larvae of many Triozidae and Calophyidae 

are strongly flattened and rounded and one might expect them to be best adapted for 

a sedentary existence, living on the surface of leaves or within open pit galls on the 

leaf surface. By contrast, larvae of many Psyllidae and Spondyliaspididae are less 

flattened and more robust, with relatively longer legs. They appear best adapted for 

a free living existence on expanding shoots or developing within larger enclosed leaf 

galls. While many species conform to this expected typology others do not. Thus, 

many Triozidae and Calophyidae live on growing shoots or within enclosed galls 

while several Psyllidae form pit galls and many Spondyliaspididae live on leaf 

surfaces. It is against this phylogenetic history that interpretations and conclusions 

regarding psyllid life history adaptations can now be made. 

Several important conclusions can be drawn from the analyses of the life history 

data. Firstly, and perhaps most significantly, the linkage between phylogenetic 

grouping and life history characteristics, while discernible, is not of overriding 

significance in determining the type of life history a psyllid undergoes. The 

phylogenetic signal, as revealed by MCA is marginally stronger at the family level



than at the generic level but at best only explains about a quarter of the total 

variation observed. Similarly, LDA on average, using life history characteristics as 

predictors, only allocates species to the correct genus, tribe or family group with at 

best 50% mean accuracy. This again suggests high within group variation in life 

history characteristics, even at ascending taxonomic levels. However, within these 

average figures there do appear to be individual taxa that display a higher level of 

predictability, such as Craspedolepta, Aphalara and Psyllopsis, but this is 

compensated for by others such as the large genus Trioza that show low 

predictability. Nevetheless, these general findings accord with Danks (2006, p. 9) 

who reviewed published data on life history traits across the Insecta. He concluded 

that: ‘‘…phylogenetic history of a group or species does determine the core structure 

of seasonal responses… but that perhaps more striking is the large number of traits 

linked to habitat or its seasonal components that have evolved many times 

independently.’’ Among such traits he lists diapause, cold-hardiness, reproductive 

pattern, paedogenesis, gall formation etc. (see also Danks (2002, 2005, 2007)). He 

concludes (2006, p. 9) that: ‘‘…how the different responses are integrated to provide 

coherent, seasonally relevant development trajectories can be understood only by 

reference to ecological demands.’’ 

Extending these conclusions to the psyllids we can observe the manner in which 

environmental and host-plant factors overlay the phylogenetic signal to produce the 

wide variation observed in psyllid life history traits observed today. Thus, the CA for 

life history variables recognizes two major groupings of linked parameters. First, 

voltinism and overwintering stage is linked to climatic environment. Second, larval 

feeding site and overwintering site is linked to plant functional type. Gall formation, 

by contrast appears to have evolved independently on several occasions across 

disparate psyllid taxa. Lerp formation is more tightly constrained within the family 

Spondyliaspididae. It should be noted, however, that plant functional type is itself 

largely a plant response to climate. 

It now becomes possible to suggest how environmental and ecological 

constraints have led to the observed diversification of psyllid life histories and to 

draw together the various threads into a coherent exposition of psyllid life history 

adaptation on a global stage. Global temperature and moisture gradients and the 

adaptive biology of host plants provide the backdrop against which such psyllid 

adaptations have evolved. 

Psyllid species living within tropical moist habitats, as typified by lowland 

tropical rainforest, probably suffer the least constraint on their development. They 

are usually associated with evergreen phanerophytes and chamaephytes, undergo 

continuous reproduction and are thus typically multivoltine. However, even in these 

benign habitats, host tree species frequently display cycles of flushing of suitable 

tissues for larval development, with individual trees at different stages of the flushing 

cycle at any one time. In such high diversity forests, a continuous life cycle demands 

continuous and effective population dispersal to seek out the sparsely distributed 

trees of the host species in an appropriate phenological state for reproduction to 

continue (Hodkinson and Casson 2000; Brown and Hodkinson 1988). It may also 

select for small and highly dispersive species (Hodkinson and Casson 2000). 

In tropical habitats with increasing seasonality of rainfall an increasing 

proportion of host tree and shrub species are deciduous, with some host species 

being leafless for several months of the year and some tree species showing various



levels of deciduousness between individuals. Under these circumstances adult and/or 

egg diapause allows associated psyllids, independent of taxonomic provenance, to 

arrest their life cycle and therby align development with the phenology of their host, 

but at the expense of a reduced number of generations per year. As tropical habitats 

become even more seasonally dry then deciduousness among hosts becomes the 

norm and seasonal diapause responses assume even greater significance for psyllid 

survival. Here again successful dispersal over a wide area may be necessary to 

relocate hosts following periods of inactivity. 

As one moves from the wet tropics into the moist temperate regions or at higher 

altitudes within the tropics a number of developments and trends in psyllid life cycles 

are observed. There is a general reduction in the temperature threshold for 

development, development rates are often slower, voltinism is reduced and life 

histories become strongly seasonal, with developmental or reproductive diapause 

becoming increasingly important for maintaining developmental synchrony with the 

host plant. Some species display morphologically distinct seasonal forms. Winter 

survival mechanisms, involving increased levels of cold-hardiness, assume increasing 

significance. There is also an increase in the availablity and use of herbaceous hostplant 

species falling within the hemicryptophyte and geophyte functional categories. 

Typically the growing tips of these plants overwinter at or below the soil surface, 

produce a flush of growth each year and then die back in the autumn. This 

necessitates a psyllid overwintering strategy that involves movement onto the winter 

bud or root or hibernation away from the host plant and movement back onto the 

new foliage in spring. 

Psyllids living on temperate phanerophytes and chamaephytes have alternative 

life history possibilities. Many psyllid species on deciduous phanerophytes overwinter 

as diapausing eggs on the buds or apical shoots where they are exposed to the full 

rigours of winter. Hatching is timed to coincide with spring bud burst. Alternatively, 

adults may overwinter either on the host or on shelter plants. In both cases a 

reproductive diapause is necessary to delay oviposition until the spring growth of the 

plant commences. Movement onto and from winter shelter plants necessitates the 

development of two phases of pre-reproductive dispersal in autumn and spring. 

On evergreen phanerophyte/chamaephyte species many psyllid species overwinter 

as diapausing larvae on the green shoots or leaves. On such plants the requirement 

for precise phenological synchrony with plant growth is less demanding as larval 

growth simply recommences as shoots or leaves resume growth in the spring. 

Development time can, as a consequence, be potentially extended beyond one year. 

Overwintering as mixed populations of eggs, larvae and adults also becomes feasible 

on such plants. 

Within temperate regions, where rainfall becomes strongly seasonal, as in areas 

of Mediterranean climate, periods of psyllid development and reproduction often 

become compressed into the short period of the year, such as early spring, when 

temperatures are sufficiently high but not too hot and when rainfall is adequate to 

stimulate the flushing of new plant growth. Such compression of life histories, with 

long periods of spent inactive as diapausing eggs, larvae or adults, becomes even 

more pronounced in psyllid species associated with host plants growing in steppe and 

desert environments. 

As one moves north from the temperate to the cold boreal regions psyllid faunas 

become much less diverse and individual species are usually associated with


prominent host taxa such as Salix, Alnus and Betula on which they typically undergo 

rapid annual life cycles during a short summer growing period. These woody host 

plants almost invariably exhibit a low chamaephyte growth form: other herbaceous 

hemicryptophytes and geophytes appear less commonly as hosts. Overwintering is 

either as eggs on growing shoots or as adults that overwinter in leaf litter around the 

base of the plants, often covered by a protective snow layer. 

It is reasonable to conclude on the previous evidence that the two prime 

environmental variables, temperate and moisture availability, acting within an 

ecological context, are either directly, or mediated through the physiognomy and 

ecological adaptations of host plants, the major pressures acting on the evolution of 

psyllid life histories. Together they have frequently resulted in similar strongly 

convergent life histories across taxonomically disparate sets of psyllid species and 

divergent life histories among related species. Danks’s (2006) conclusions regarding 

the comparatively low importance of group phylogenetic history in determining life 

history parameters are well supported by the psyllid data. 

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