Southern Potato Wireworm


Conoderus falli Lane, Elateridae, COLEOPTERA

DESCRIPTION

Adult - The adult, 6 mm to 8.5 mm long, is a brownish, oblong click beetle. Its legs are light tan.

Egg - The spherical egg is smooth and translucent white with an average diameter of 0.5 mm.

Larva - The newly hatched larva is white and later becomes cream colored or yellowish-gray with a reddish-orange head. The fully grown larva is about 17 mm long. 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 but soon changes to a creamy yellow.


BIOLOGY

Distribution - The southern potato wireworm was apparently introduced into the U.S. from South America. In this country, it has been reported on coasts from North Carolina to Louisiana. Within North Carolina, it occurs mainly in the southeastern counties of the Coastal Plain.

Host Plants - The southern potato wireworm appears to prefer potato tubers. Newly transplanted tobacco seedlings, roots of sweet potatoes, carrots, corn seedlings, and stems of tomato transplants are also frequently attacked. Less frequently damaged hosts are melons, the roots of beets, and the fruits of strawberries, cantaloupes, watermelons, and tomatoes that touch the soul surface.

Damage - Wireworms chew ragged holes on the roots. Oftentimes a single root may have 10 or more small holes. Early feeding appears as shallow but large cavities. Late or most recent feeding appears as ragged, deep holes. This wireworm usually attacks sweet potatoes late in the season.

Life History - While the biology of this insect pest has not been studied in North Carolina, in South Carolina adults are found in fields throughout the year. There are two generations annually. 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. They hatch into the "short-cycle" brood, which requires 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 the overwintering generation, which requires 239 to 318 days for the eggs to reach adulthood.


CONTROL

No insect parasites or predators of this wireworm have been discovered. Three disease-causing agents - a fungus, a protozoan, and a parasitic nematode - have been isolated, but their usefulness in the control of this wireworm has not been determined.

As a cultural control, susceptible crops should not be planted in fields that were planted with a winter crop, those not plowed during the fall and winter, or those not recently in row crops. No resistance to this pest has been found in Irish potatoes. However, the sweet potato varieties Nugget and All Gold do possess some resistance.

Insecticides for the control of wireworms can be applied in furrow at planting, broadcast and incorporated into the soil, or broadcast later over the top of sweet potato foliage. A problem has been this wireworm's development of resistance to chlorinated hydrocarbons and organophosphate insecticides. Therefore, for specific information or insecticides and rates, consult the current North Carolina Agricultural Chemicals Manual.

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