Natural selection plays the central role in shaping the biological world, yet its glacial pace makes the evolutionary change occurring around us appear all but invisible. Occasionally, exceptional circumstances permit us to witness the process of natural selection. Such circumstances exist today in an expanding area of Illinois, Indiana, Ohio, and Michigan: the behavior of the western corn rootworm (Diabrotica virgifera virgifera), an important pest of corn, has been shifting since the mid-1980s under intensive selection by annual crop rotation, allowing it to circumvent our single most cost-effective and environmentally benign management tool. The failure of crop rotation presents us with an exceptional opportunity to study evolution in our midst while working toward a solution to one of the most vexing agricultural problems of our time.
Rotation resistance involves frequent beetle flight between corn and crops rotated with corn to lay eggs and feed in both areas. Beetles that once laid all of their eggs in cornfields are now laying many of their eggs in soybeans and other crops. By hedging their egg-laying bets and depositing eggs in many places, female beetles assure that some of their eggs will hatch in cornfields the following spring where their larvae will find the corn roots they need to survive.
Male western corn rootworm on soybean leaf.
For most insect problems, our first response has been to use insecticides as "fire-fighting tools" in an attempt to quench a pest outbreak before it has a chance to rage out of control. For many insects, we possess a number of effective options and at worst suffer only spotty "scorchings" in the process of gaining control. Crop rotation-resistant western corn rootworms are different. In essence we have learned that widespread use of our best western corn rootworm fire-fighting tool, annual crop rotation, sparked a behavioral resistance to rotation that is spreading like a prairie fire across the Corn Belt, the flames of which we are ill-equipped to fight. Many of the insecticides that serve as our second line of defense against the western corn rootworm are in jeopardy of losing their registrations with the EPA. Without crop rotation or soil insecticides and with transgenic corn for rootworms not yet a commercial reality, growers have few options for extinguishing a rotation-resistant western corn rootworm problem. The potential added cost to Illinois growers (more than $100 million annually) of the rotation-resistant western corn rootworm is substantial, and the potential economic and environmental impact of crop rotation's collapse across all the Corn Belt states would be staggering.
Beginning this summer, western corn rootworm research at the Illinois Natural History Survey and the University of Illinois will make a quantum leap in its scope. Mindful of the threat to corn production and the urgency of mounting a multipronged attack on this problem, the Illinois Council on Food and Agricultural Research (C-FAR) recently awarded the University of Illinois/Illinois Natural History Survey western corn rootworm research team a three-year $1,083,900 grant to study the western corn rootworm through its inaugural C-FAR Sentinel Grants Program.
Western corn rootworms decimating a soybean leaf.
The purpose of the project ("Crop Rotation Collapses as a Pest Management Tool for Western Corn Rootworms: In Search of a Solution") is to broaden the study of this problem well beyond the "fire-fighting" stage. Though rotation resistance is fundamentally a problem of movement (i.e., beetles now leave corn to lay their eggs), to understand it we must study factors that influence movement across the biological spectrum, from gene expression to agroecology. Our goals include development of a mechanistic understanding of rootworm movement and rotation resistance, improvement of grower management options, prediction of the continuing expansion of the affected area, and identification of a genetic signature for the adaptation. The new support will expand our capacity to investigate the biology and ecology of the western corn rootworm while applying the latest molecular techniques to seek a genetic understanding of rotation resistance.
The project involves scientists from the Illinois Natural History Survey (Joseph Spencer and Eli Levine); the University of Illinois Departments of Crop Sciences (Mike Gray and Sue Ratcliffe), Geography (Scott Isard), Natural Resources and Environmental Sciences (David Onstad), Entomology (Hugh Robertson), and Texas A&M University (Paul Mitchell); along with researchers at the Keck Center for Comparative and Functional Genomics (Harris Lewin, Mark Band, Jose Pardinas, and Lei Liu). The research team combines diverse expertise, years of experience, and a wealth of scientific resources needed to address rotation-resistance at multiple levels of analysis.
C-FAR supports research in Illinois that 1) expands markets and profitability for our agricultural products, 2) discovers and develops alternative products, practices, and enterprises that enhance healthy urban and rural communities, 3) increases our capacity to address the world's changing food and agricultural demands, 4) improves food quality and safety, and 5) facilitates sustainable use of our natural resources. Sentinel Grant Program funding is intended for projects with a broad scope and interdisciplinary flavor, needing substantial support to address a problem of significance to Illinois. Our goal is restoration of crop rotation to its former utility as a cultural control for management of western corn rootworms.
Joseph L. Spencer, Eli Levine, and David W. Onstad, Center for Economic Entomology; Michael E. Gray and Scott A. Isard, University of Illinois
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