Aleurodicus dispersus (whitefly)

Immature and adult stages of A. dispersus cause direct feeding damage by sucking plant sap, which can cause premature leaf fall (EPPO, 2006). In cassava (Manihot esculenta), A. dispersus infestation caused yellowish speckling of the leaves and in severe infestation the leaves crinkled and curled. Infestation spread from the bottom leaves to the top (Palaniswami et al., 1995). Symptoms of infection are mosaic, leaf and vein discolouration and tissue distor­tion such as curling and crinkling or wrinkling (Costa, 1969). However, A. dispersus was mostly commonly impli­cated as a vector and has been associated with more than 25 different diseases and feeds on a larger number of plant species (Russell, 1965; Costa, 1969). Plants are also disfigured and may be unmarketable (EPPO, 2006). Boopathi (2013) described the intensity of damage by using seven grade.

Indirect damage is due to the heavy production of honeydew and white, waxy material produced by the insect. Copious honeydew is excreted which coats surrounding surfaces and often develops a layer of sooty mould.

Biological Control

Aleurodicus dispersus was first recorded in Hawaii in 1978, after which it spread rapidly. Its pest status on guavas (Psidium guajava) stimulated a successful biological control programme (Kumashiro et al., 1983; Beardsley, 1993). The introduction and establishment of the coccinellid beetle Nephaspis oculatus (N. amnicola) and the parasitoid Encarsia haitiensis successfully controlled A. dispersus on guavas in highland and lowland areas of Honolulu, Hawaii. In 1980-1981, peak population densities of A. dispersus were reduced by 79% in the lowlands and 98.8% in the highlands. Rainfall, temperature and previously established predators, particularly Allograpta obliqua, probably also contributed to the reduction of A. dispersus populations (Kumashiro et al., 1983). Mallada astur and Cybocephalus spp. were found to be the most efficient predator in reducing the population of A. dispersus in India (Boopathi, 2013). Inundative releases of Cryptolaemus montrouzieri and M. astur against A. dispersus had only in temporary reduction of the whiteflies during 1998-1999 in Karnataka (Mani et al., 2001).

Since the biological control of A. dispersus in Hawaii, there have been further successes on Pacific Islands; for a review see Waterhouse and Norris (1989). In each case, E. haitiensis was successful, aided by one or more of the introduced coccinellids.

A biological programme in tropical Africa was described by Neuenschwander (1996), in which two exotic hymenopterous parasitoids were introduced. These helped control A. dispersus populations, with indigenous coccinellids playing a minor role. A. dispersus was observed in Benin for the first time in 1993, along with the parasitoids E. haitiensis and E. guadeloupae, which were thought to have been accidentally introduced. Between 1993 and 1996, these parasitoids helped control A. dispersus populations on guava (D'Almeida et al., 1998). E. haitiensis has been successfully introduced into Queensland, as part of the biological control of A. dispersus in Australia (Lambkin, 1998). In India, E. guadeloupae was found to be the most effective parasitoid in the reduction of A. dispersus population on cassava (Manihot esculenta) and eggplant (Solanum melongena; Boopathi, 2013) and Boopathi et al. (2015a, b) evaluated the entomopathogenic fungi Beauveria bassiana, Metarhizium anisopliae, Lecanicillium lecanii and Isaria fumosorosea [Cordyceps fumosorosea] were tested for their efficacy in managing the A. dispersus on cassava and eggplant in India. The fungi I. fumosorosea [C. fumosorosea] and L. lecanii exhibited promising levels of control (>70% mortality). L. lecanii at 1.33 x 10⁷ and Verticel at 7.5 g/l were found to be most effective against A. dispersus at 7, 15 and 21 days after spraying (Mallappanavar, 2000).