Southern Potato Wireworm
Egg - The spherical egg is smooth and translucent white, with an average diameter of 0.5 mm.
Larva - The newly hatched larva is white, later becoming cream colored or yellowish-gray with a reddish-orange head. The mature larva may be as long as 17 mm. The last abdominal segment of this larva, unlike that of the tobacco wireworm, terminates in a closed oval notch rather than a V-shaped notch.
Pupa - Slightly larger than the adult, the pupa is white when first formed, soon changing to a creamy yellow.
Host Plants - The southern potato wireworm appears to prefer potato tubers. Newly transplanted tobacco seedlings, the roots of sweet potatoes, carrots, corn seedlings, and the stems of tomato transplants are also frequently attacked. Less frequently damaged hosts are melons, the roots of beets, the fruit of strawberries, and tomatoes that touch the soil surface. Seeds of various small grains, grasses, and sorghums are damaged.
Damage - Damage from this insect is most severe in nonrotated or minimum-till corn fields of the South. These wireworms threaten the establishment of vigorous stands of field corn by feeding on germinating seeds and the roots of corn seedlings. Above ground, symptoms appear as tip dieback. Later symptoms include yellow streaking in leaves of older plants or severe wilting. Underground symptoms include tunnels in the root crown, a jelly-like exudation from injured corn stems, and root pruning. In severe infestations, tunneling in the roots of larger plants has been observed.
Life History - Although adults are found in fields throughout the year in some areas of South Carolina, southern potato wireworms are believed to overwinter as larvae in North Carolina. Their biology, however, has not been studied in this state. Adults from overwintering larvae begin to appear in large numbers during May, reaching their peak abundance in June. Each first generation female lays an average of 36 eggs. The larvae which emerge comprise the "short-cycle" brood and require 42 to 109 days to mature. Adults of this "short-cycle" brood are abundant in late August and in September. They mate and lay eggs of the "long- cycle" brood, or overwintering generation, which requires 239 to 318 days for development from egg to adulthood. There are two generations annually.
Rotation to nonhost crops such as soybeans should be the first defense. At planting, in-furrow applications of granular insecticides have been used successfully to control this pest in corn fields, but use is limited by expense and by variability in wireworm populations. A problem has been this wireworm's development of resistance to some chlorinated hydrocarbon and organophosphate insecticides. For up-to-date control information, consult the current North Carolina Agricultural Chemicals Manual.