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The Other Guys: Don't Forget About Secondary Insect Pests

Kevin L. Steffey
Kevin L. Steffey
Professor and Extension Entomology Specialist
Department of Crop Sciences
(217) 333-6652; ksteffey@illinois.edu
Nathan L. Wentworth
Nathan L. Wentworth
Graduate Research Assistant
Department of Crop Sciences
(217) 244-2124; nwentwor@illinois.edu

Corn rootworms have earned the designation as “the billion dollar bug,” and justifiably so. Year in and year out,corn rootworms are the most destructive pests of corn throughout the Corn Belt. However, in recent years, damage caused by so-called secondary insect pests has become more prevalent. Secondary soil insect pests—e.g., grape colaspis, white grubs, and wireworms—cause injury to corn early in the season. It’s probable that the trend toward early planting has elevated the importance of these pests. At a time when secondary soil insect pests have become more problematic, the tools for management ofall subterraneaninsects that affect corn have changed.

figure 1Although granular and liquid insecticides still can be used to control soil-dwelling insects in corn, new insecticidal seed treatments and transgenic hybrids have expanded the list of options. With more options for control of soil insect pests, management scenarios are changing.

The newest insecticidal seed treatments are nicotinoids, including clothianidin (Poncho), imidacloprid (Gaucho and Prescribe), and thiamethoxam (Cruiser). These systemic products provide control of an array of subterranean insects, as well as some insects that feed above ground (e.g., flea beetles and southern corn leaf beetles). The higher rates of these products also are intended for control of corn rootworms.

figure 2Early in 2003, the EPA approved the registration of Monsanto’s MON 863 event (containing the Bt Cry3Bb1 protein) for control of corn rootworms. YieldGard Rootworm® hybrids were available on a limited basis in 2003 and will be more widely available in 2004. These hybrids offer no control of secondary pests such as white grubs and wireworms. In addition, the resistance management plan for YieldGard Rootworm hybrids includes a minimum 20 percent non-transgenic refuge. Consequently, there is a potential need for control of secondary insects in fields of YieldGard Rootworm corn and in refuge acres. So, the future for management of soil insects that damage corn likely will be some combination of insecticides (granules, liquids, and/or seed treatments) and transgenic hybrids.

The increased prevalence of secondary insects and the changes in management of soil insect pests of corn demand improved knowledge of the biology and economic impacts of secondary insect pests. We have focused recent research efforts on the Japanese beetle, Popillia japonica, an insect that causes injury to corn in both its larval and adult stages. Japanese beetle grubs feed on corn roots early in the season, and the adults feed on corn silks in July, potentially interfering with pollination. In multiple trials established in 2003, the impact of both types of injury has been investigated. Preliminary results from these studies will be presented.

For the development of future IPM programs that ensure appropriate use of insect-control technology, we need to learn much more about the prevalence and impact of secondary insect pests of corn. Modern scientific literature offers few answers to questions about these pests. Through surveys and targeted research efforts, we hope to accumulate a body of knowledge that will enable growers to select the right strategies for managing these troublesome pests.

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Department of Crop Sciences
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