Female Mate Choice and Fitness Components in Western Corn Rootworm in Relation to Cry3Bb1 Susceptible and Resistant Genotypes

The success of transgenic (Bt) corn to control corn rootworm populations is dependent on high dosage, a refuge of non-Bt corn, and random mating between resistant and susceptible beetles. Resistant populations of western corn rootworm (WCR) have easily been selected for in the lab and currently are being observed throughout the U.S. Corn Belt, possibly related to lack of fitness costs due to lower dosage than expected and/or non-random mating between resistant and susceptible beetles. Non-random mating occurs through male-male competition and/or female choice. To examine whether female WCR prefer to mate with males of similar genotype, we paired combinations of laboratory selected Bt resistant and susceptible males and females. Neither the proportion of pairs that copulated successfully (42%) nor courtship duration varied significantly with genotype; however, copulation duration was shortest for resistant males crossed with susceptible females. Although the genotype of the mating partner had no effect on female longevity, fecundity, or viable egg production, body weight was highly correlated in mated but not unmated pairs. Consequently, with the newly marketed, high-dose pyramid Bt corn available for corn rootworm control or with future high-dose events, the survival of corn rootworms on transgenic crops may correlate with smaller body size, which could promote positive assortative mating among resistant beetles, enhance the spread of resistance, and decrease the durability of the transgenic corn. Ultimately, this new fundamental knowledge of WCR biology and behavior will lead to better corn rootworm resistance management plans.