Wireworm, Coleoptera: Elateridae

Description

Several species of wireworms occur in Arkansas and descriptions of the different species vary. In general, wireworm adults, also known as click beetles, are dark brown hard bodied beetles. The term “click” comes from the ability to snap the hinge between the thorax and abdomen resulting in a flip that rights the upturned insect. Size varies but adult wireworms in grain sorghum are about 1.25 inch long. Larvae occur in the soil. Although the larvae of some species are white, the most common in Arkansas is tan and at maturity about 3/4 inch in length (Photo 6). True legs are evident and the head is somewhat flattened.

Distribution, damage and impact

Wireworms occur throughout the state but the major damage resulting from their feeding has been observed in Clay County in northeast Arkansas and near Paris in Logan County. Larvae feed on newly planted seed, emerging seedlings, and can be found infesting the lower stems of larger grain sorghum plants. Damage in some fields has been substantial and at times fields have been replanted due to stand loss.

Life History

The biology of wireworms is also quite variable. Some species complete two generations per year while some require up to 5 years for a single generation. In general, adults emerge from overwintering larvae in the spring and search for grassy fields. Eggs are laid in the soil usually where grasses are available for the larvae to feed. When grain sorghum is planted the seed and emerging seedlings are burrowed into. Seedlings can be weakened and killed. Wireworm larvae can be found by carefully digging up weak seedlings and searching the soil. In dry conditions wireworm larvae move deep into the soil and are difficult to detect.

Management

In Arkansas avoidance of recently plowed grassy fields including pastures will reduce the likelihood of damage from wireworms. Crop rotations, i.e., grain sorghum following a broadleaf like soybean, will reduce damage but with wireworms that require multiple years for development, damage may be substantial. Damage also is more severe in fields where seed are slow to germinate and where seedling growth is retarded. Thus, delaying planting until soil is warmer may reduce the impact of the wireworms. Although the use of treated seed and soil insecticides applied at planting may provide some control, wireworm problems persist in Clay County despite insecticide application. Foliar insecticide application to seedlings is of no benefit.

Insecticide recommendations for wireworms on grain sorghum

See Table 1 for insecticide recommendations current at time of publishing. Current updated recommendations can be found in the Cooperative Extension Service publication MP-144 and on the world wide web at WWW.cdms.net/manuf/default.asp. Always follow instructions on pesticide labels.