Tobacco Wireworm
Conoderus vespertinus (Fabricius), Elateridae, COLEOPTERA


DESCRIPTION

Adult - The adult, called a click beetle, is oblong and about 8.5 mm in length, thought the size varies considerably. It has a distinct and characteristic pattern of light and dark brown markings on the thorax and elytra.

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

Larva - The newly hatched larva is white and approximately 1.5 mm long. The mature larva reaches a length of 14 to 19 mm. 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 and Piedmont. It is much more prevalent in areas where tobacco or corn are the main crops than in areas planted chiefly with truck crops. Grassy and weedy fields are characteristically infested.

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

Damage - The tobacco wireworm is one of several species of wireworms which reduce field corn stands in North Carolina. Problems with this insect result primarily from continual planting of corn in the same field. Larval feeding on newly planted corn seeds causes poor germination and stunted, spindly, chlorotic plants which often die or are nonproductive. The typical above ground symptom is a distinct yellow streaking of the terminal blades. Wireworm damage consists of one or more ragged holes on the underground stem and extensive root pruning in older seedlings.

Life History - The eggs (240 per female) are laid singly on, or slightly beneath, the soil surface in the summer. Larvae hatch and feed on the roots of corn or other plants. The winter is passed in the larval stage. When corn is planted the following spring, these wireworms feed on the germinating seeds and young seedlings. Pupation then occurs in the soil, and adults emerge during early summer. There is only one generation per year. The average life cycle requires about 348 days in North Carolina, as follows: egg, 10 days; larva, 315 days; pupa, 10 days; and preoviposition period, 13 days.


CONTROL

Because infestations occur erratically, controls are still only speculative. Crop rotation is an effective management tool for control and should be practiced where possible. Granular insecticides have proven beneficial on highly susceptible fields. For specific control information, consult the current North Carolina Agricultural Chemicals Manual.