Social and environmental factors affecting western corn rootworm tolerance of host crop rotations

Rudy, A., B. Thomas, and C. Harris

Presented at the All Scientist Meeting (2003-09-12 )

Western Corn Rootworm (WCR) in the Midwestern United States illustrates the ways that social factors and biophysical environmental factors interact in agricultural pest systems. The conventional wisdom has been that two- or three-year corn-soybean (or corn-soy-wheat) rotations act as a low-input, non-resistance inducing, means of holding WCR populations below economic damage thresholds. Recently, WCR “behavioral variants” have been found in areas near the Illinois-Indiana border and in isolated areas in Michigan and Ohio. These “rotation resistant” WCR have adapted to rotations and lay eggs in fields planted with soybeans, which leads to WCR populations in first-year corn near, at or above economic thresholds. Feeding assays and field studies by O’Neal et al. (2002) suggest that the WCR variant’s behavior may be derived less from the development of a new genotype and more from the expression of already-present, but heretofore unnecessary, behavioral plasticity induced by new and unevenly distributed agroecological conditions. Our hypothesis is that the emergence of the WCR behavioral variant is largely caused by regional changes in cultivation practices – earlier planting dates and/or planting of new varieties that are more cold-hardy – which have disrupted the synchronicity between corn phenology and WCR development. A second-order hypothesis is that the unevenness of the distribution of the variant is associated with the distribution of rotational and crop-mixture diversity. The purpose of our study is to identify whether or not cultural practices and corn variety selection have changed in the spatial and temporal manner coincident with the arrival of WCR “behavioral variants” and with our hypotheses. Interviews with extension agents, farmers, and seed company representatives make it possible to determine examine these agroecological changes as they have developed over the past 20 years focus on crop rotations, pesticide applications, and crops planted.

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