Evaluating the effect of foliar insecticides on populations of suspected Bt-resistant western corn rootworm beetles in rotated soybean

The western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte, is the most economically significant insect pest of U.S. corn production and can inflict substantial yield loss. Historically, crop rotation was a successful management strategy because oviposition occurred predominantly in corn. However, beginning in 1995, crop rotation failures were seen in Illinois and Indiana. Commercial Bt corn hybrids targeting this pest were widely adopted and were an effective tool to manage rotation-resistant WCR. Until recently, Documentation of field-evolved WCR resistance to Bt traits was associated with the cultivation of continuous corn expressing the same Bt toxin. In 2013, severe injury to rotated Bt corn was documented in Illinois, adding urgency to existing concerns about Bt resistance. Unexpected WCR injury to Bt corn hybrids in rotated cornfields and high beetle densities in corn and soybeans have increased grower interest in adult management. In 2014, we initiated a three-year experiment to determine how applying foliar insecticides to soybean affects patterns of WCR beetle abundance at trial sites where resistance to Cry3Bb1 is suspected. Treatments are soybean foliar-applied insecticide and include: (1) an early application of Warrior II (lambda-cyhalothrin) applied during the tasseling stage of nearby corn, (2) a late application of Warrior II applied when nearby corn silks are brown, and (3) an untreated check. Adult WCR abundance was evaluated using unbaited yellow sticky traps and sweep samples. Data and interpretation will be presented from the 2014 and 2015 growing seasons.