How Kansas Crop Consultants Scout for Western Corn Rootworms (Coleoptera: Chrysomelidae) in Field Corn

Abstract

The western corn rootworm (Diabrotica virgifera virgifera LeConte) is one of the most important insect pests of corn in North America. This insect costs farmers $1 billion or more annually in reduced yields and insecticide treatment costs (Metcalf 1986). Corn rootworm larvae damage the corn root system by feeding underground. The root feeding can cause physiological yield losses and make the plants susceptible to lodging and stalk rot fungi (Palmer and Kommedahl 1969). Corn rootworm beetles also cause damage by feeding on silks, which affects pollination and seed set. Corn rootworms traditionally have been managed on a field-by-field basis using crop rotation or insecticide applications. Crop rotation works because corn rootworm beetles tend to lay their eggs in corn fields. of treated areas. They also are seeking to use timely applications of environmentally friendly insecticides to replace standard foliar insecticide treatments. The USDA and cooperating university researchers have evaluated areawide management for controlling western corn rootworm beetles in several large, 41 km2 regions (16 mi2) (Faust and Chandler 1998, Wilde et al. 1998, Chandler 2003). The objective of these projects was to reduce the frequency and number of insecticide applications needed to achieve commercially acceptable suppression of western corn rootworm. The areawide management strategy requires information on corn rootworm populations within the managed area. One method of estimating corn rootworm beetle populations is for scouts to count beetles on corn plants at numerous locations in the The eggs overwinter and hatch in the spring when corn plants are growing rapidly. Crop rotation reduces the likelihood that corn will be planted in soil where large numbers of western corn rootworm eggs have been laid. In some areas, however, the economic advantage of corn production is so large that growers plant corn year after year in the same fields (known as continuous corn). In this case, growers use soil insecticides to protect the plant roots from corn rootworm feeding or foliar insecticide treatments to kill the beetles before they can lay their eggs in the field. Scientists have proposed using an areawide management strategy to manage corn rootworms (Wilde et al. 1998, Whitworth et al. 2004) by reducing insect populations (in this case beetles) over a larger geographical area to reduce the threat of reinfestation