Matings between western corn rootworms from refuge and Bt corn are not evenly distributed in cornfields with structured refuges

Western corn rootworms (Diabrotic virgifera virgifera LeConte) are the most economically important U.S. pests of corn.  Since 2003, U.S. corn producers have increasingly used Bt (Bacillus thuringiensis Berliner) corn hybrids that express toxic Cry proteins to manage corn root injury caused by larval feeding.  To slow the evolution of resistance, US-EPA requires that producers growing Bt corn hybrids deploy a non-Bt refuge within each Bt cornfield.  The refuge provides a location where rootworms can develop without exposure to Bt toxins.  Use of refuges as part of an insect resistance management strategy carries expectations including that beetles developing on refuge plants will move into Bt corn and mate with the potentially-resistant beetles that survived larval exposure to Bt toxins.  These pairings should yield offspring that are susceptible to Bt toxins.  We studied the distribution patterns of single and mating adults in four refuge configurations (20% structured refuge, 5% structured refuge, 5% seed blend refuge and 0% refuge) for three years (2010-2012).  Our data reveal that most western corn rootworm beetles reside and mate in and near refuges.  The gut contents of each partner in a mating pair were analyzed to determine whether they had been consumed Bt or non-Bt corn tissue prior to mating.  Among the 864 mating pairs collected, 8% were mixed-matings between individuals from refuge and Bt corn.  In structured refuge treatments, these mixed-matings were found predominately near the interface between refuge and Bt corn.  The implications of this information on insect resistance management will be discussed.