Evaluating microbial seed treatments in combination with transgenic corn as a defense against Western corn rootworm (Diabrotica virgifera virgifera)

The purpose of this project is to determine the potential applicability of beneficial microbes applied as seed treatments to manage Western corn rootworm (Diabrotica virgifera virgifera, or WCR) resistance to transgenic (Bacillus thuringiensis- expressing, or Bt) crops.  The rootworm complex, which includes WCR, is considered the most important pest of corn worldwide, and WCR resistance to Bt corn has already been documented (Gassmann 2011).  Our preliminary behavioral assays have shown that WCR does indeed detect and avoid certain pathogenic and non-pathogenic microbes.  Moreover, the degree of avoidance behavior is dependent upon the microbe species tested.  For examples, when given a choice between inoculated and non-inoculated corn seeds, insects display strong avoidance to Metarhizium spp., a lesser degree of avoidance to Beauveria bassiana, and, interestingly, an attraction to Serratia marcescens.  Preliminary behavioral assays have also shown insect avoidance of non-pathogenic bacteria and fungi that form symbiotic relationships with plant root tissue.  These symbiotic microbes are commonly sold as plant treatments for increasing root growth and increasing resistance to plant pathogens.  Our previous research has also shown WCR behavioral avoidance of Bt corn.  However, the interactions between these two behavioral stimuli have yet to be investigated.  We will examine the combined effects of microbes and transgenic corn on WCR behavior, survival, and performance, under both laboratory and greenhouse conditions.