Tobacco Wireworm
Conoderus vespertinus (Fabricius), Elateridae, COLEOPTERA


DESCRIPTION

Adult - The adult, called a click beetle, is reddish-brown with yellow markings, oblong, and about 8.5 mm in length, though the size varies considerably.

Egg - The newly laid egg is spherical, white and about 0.5 mm in diameter.

Larva - The newly hatched larva is approximately 1.5 mm long and grows to a length of 14 to 19 mm. Except for the head, which is tinged iron brown, the larva is white. Its last abdominal segment terminates in a V-shaped notch.

Pupa - The brown pupa is slightly larger than the adult; it occurs in the soil near the food source.


BIOLOGY

Distribution - The tobacco wireworm is common in the southeastern states. In North Carolina it occurs throughout most of the Coastal Plain. It is much more prevalent in areas where tobacco, cotton or corn are the main crops than in areas planted chiefly with truck crops.

Host Plants - The tobacco wireworm apparently prefers tobacco, but it feeds on a variety of other plants including cotton, corn, potatoes, sweet potatoes, and various truck crops.

Damage - Damage occurs as ragged holes in 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. Damaged roots are downgraded or discarded.

Life History - Eggs, averaging 240 per female, are laid singly on, or slightly beneath, the soil surface in summer. Larvae hatch and feed on roots of corn, tobacco, potato and other plants. Winter is passed in the larval stage. Pupation in June occurs in the soil. Adults emerge during early summer with greatest activity from late June through July. There is only one generation per year. The typical life cycle requires about 348 days in North Carolina: egg, 10 days; larva, 315 days; pupa, 10 days; and preoviposition period, 13 days.


CONTROL

Crop rotation is an effective management tool for control and should be practiced where possible. Fields planted to a winter cover crop, those not plowed during fall and winter, and those not recently in row crops are not suitable sites to plant wireworm-susceptible crops. Low soil moisture, high summer temperatures, disease, predation and cannibalism are helpful in reducing wireworm populations.

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. For specific information on insecticides and rates, consult the current North Carolina Agricultural Chemicals Manual.

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