Field and laboratory methods for estimating variant western corn rootworm (Coleoptera: Chrysomelidae) risk to rotated corn
Abstract
A variant strain of the western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte, poses a management problem to growers in parts of Indiana and the Midwestern United States by circumventing crop rotation, a formerly successful management strategy. The loss of ovipositional fidelity to corn by this variant results in oviposition by WCR adults into the alternate crop, normally soybeans. New sampling methods are desired to better inform growers of the regional and site-specific risks of damage to first-year rotated corn. A sampling program was conducted at multiple locations throughout Indiana from late July through early August of 2006, 2007, and 2008. Sites were chosen to correspond to a variety of historical variant WCR pressure levels in different parts of the state. As expected, results showed historically higher variant WCR pressure areas corresponding with higher numbers of WCR adults being captured. Soybean herbivory by WCR females is a potential marker for oviposition levels in soybeans and, therefore, the risk of damage to first-year corn grown the following year. Efforts were made to develop a laboratory assay capable of measuring soybean herbivory levels using indirect-ELISA and digital image analysis techniques. Indirect-ELISA proved to be unsuccessful in this aim due to insufficient levels of protein in mature soybean foliage and insufficient specificity of the polyclonal antisera used. Digital image analysis, however, showed promise as a suitable technique. This analysis exploited the characteristic dark-green color of the abdomens of most soybean foliage-feeders. Type I error rates were acceptable when negative controls (beetles reared on corn and known not to have soybean foliage within their guts) were analyzed using this method. When this method was applied to field collected beetles, beetles from low variant pressure-level areas showed lower rates of soybean herbivory than those from moderate or high pressure-level areas. The potential utility of this method to growers and consultants is discussed.
Degree
M.S.
Advisors
Richmond, Purdue University.
Subject Area
Organismal biology
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