Melanotus communis (common wireworm)

Characteristically, crops will show symptoms only in a restricted part of infested fields where hosts that have been attacked may appear stunted or wilted, as a consequence of larval root feeding. Seedlings and young plants are especially vulnerable, although older plants can also be attacked. Maize plants can establish poorly if kernels are attacked and completely eaten out, preventing germination. Potato tubers with small holes in their surface could indicate damage by M. communis. Other symptoms on potato tubers and carrots are narrow scars up to 3 mm diameter and up to 2 mm deep (Jansson and Seal, 1994).Ingerson-Mahar et al. (1997) provide illustrations of damage symptoms.

Cultural methods of controlling wireworms include summer ploughing of fallow fields and crop rotation. Ploughing to a depth of approximately 25 cm in late summer will dry out the soil and break up the insects' pupal chambers, killing large numbers of pupae and adults. It will also expose them to predators. Legumes are more tolerant to feeding by these pests and are therefore excellent crops with which to rotate maize. Rotating maize with small grains and planting crops in well-drained soils are additional control measures effective against M. communis (Anon., 1982).
M. communis populations are reduced by discing the soil before planting. This physically injures the larvae and brings them to the soil surface where they can dessicate or be predated on by birds. However, this does not prevent M. communis from reaching economically damaging levels in Florida, USA, where soil insecticides or flooding of fields are tactics that are also used (Hall and Cherry, 1993). In sugarcane, short-term flooding lasting from 7 to 21 days has been shown to be a potential measure to control wireworm damage (Glaz and Cherry, 2003). Longer periods of flooding can be deleterious to the crop. For example, 6 weeks of flooding caused 72% mortality of M. communis larvae in Florida sugarcane trials, but ratoon cane production was reduced due to the flooding, with yields of only 20-120 t/ha compared with yields of 85-216 t/ha from the unflooded (control) sugarcane (Deren et al., 1993).

Hall and Cherry (1993) provide an equation (Y = -94.4 + 7.1F + 4.3C2, where Y is the expected percentage mortality, F is flood duration in weeks, and C2 is temperature in degrees Celsius). The equation may be used to estimate how long a flood should be continued at a given temperature to obtain a desired level of M. communis control.

Seeds susceptible to M. commnuis larval damage have been coated with potential feeding deterrents and tested (Villani and Gould, 1985a). Maize seed coated with crude extracts of butterfly milkweed (Asclepias tuberosa) acted as a significant feeding deterrent (Villani and Gould, 1985b).

Before applying any chemical insecticides against wireworms, the use of baits is recommended for pre-planting sampling in potato fields in southern Florida (Jansson and Lecrone, 1989). Of eight insecticides tested by Hall and Cherry (1985), chlorpyrifos was the least toxic insecticide tested. In separate tests, among six candidate insecticides studied in laboratory trials, bifenthrin and thiamethoxam reduced damage by wireworms to germinating eyes of sugar cane seed planted in organic soils. The chemicals did not cause great mortality but repelled the wireworms (Hall, 2003). 

M. communis larvae can attack seeds, germinating seedlings, tubers and the roots of well-established plants. Most plants are attacked in the early summer, although in cooler years larvae develop more slowly and feed longer, so plants continue to be attacked later into the year (Riley et al., 1974). The most significant damage is incurred by germinating seeds and seedling plants. Seeds can be hollowed out, thus preventing germination. M. communis does more damage in fields that have been grassy or weedy the preceding year (Anon., 1982). Much of the literature concerning the impact of M. communis damage concentrates on sugarcane or potatoes.Damage to sugarcaneM. communis can be the most abundant and largest elaterid species found in sugarcane fields in Florida, USA, hence it is the most significant (Cherry, 1988). Larval feeding can cause significant economic damage. Hall (1990) quantified damage to sugarcane by M. communis larvae in small and large plot tests. Stand reduction varied from 6.2 to 7.8% per wireworm per 1.5-m row, 12 weeks after planting. However, tillering during the growing season compensated to some degree for early stand losses, but at harvest, stalks from plots infested by elaterids tended to weigh less. At harvest, the weight of cane harvested was reduced by 3.8% per larvae per 1.5-m row, the equivalent of a yield loss of 5.9 metric tons per larvae per 1.5-m row. Larvae did not cause reductions in sucrose levels in juice. However, because cane weight at harvest was reduced, the amount of sugar produced was reduced by the same amount.Damage to potatoes and other cropsThe most serious damage to potatoes is caused to developing tubers (Wolfenbarger, 1965). Third-instar larvae make very narrow and shallow holes 1 mm deep in potato and carrots. Older instars make deeper holes up to 3 mm diameter and 2 mm deep (Jansson and Seal, 1994). In trials, 30-48% of tubers in untreated potato plots suffered injuries, largely due to M. communis (Baranowski and Waddill, 1975). In southern Florida, USA, wireworms are the most serious insect pests of potatoes, with M. communis being the most important. In two consecutive growing seasons in the 1980s, up to 45% of many potato crops were downgraded due to damage from wireworms (Jansson and Lecrone, 1989). M. communis has been the single most important constraint on potato production in southern Florida (Jansson and Seal, 1994). In trials in Florida, where potato crops are grown following summer cover crops, delaying the planting of the summer crop can reduce wireworm damage to tubers the following season by nearly 10% and save $1,300 to $3,300 per ha (Jansson and Lecrone, 1991).Wireworms, including M. communis, play only a minor role in groundnut pod damage (Herbert et al., 1992).