Characteristics of mating western corn rootworms, Diabrotica virgifera virgifera LeConte, in refuge and Bt corn

Western corn rootworm, Diabrotica virgifera virgifera LeConte, has been managed using Bt, Bacillus thuringiensis Berliner, corn hybrids since 2003. To delay resistance to Bt toxins, US EPA requires that non-transgenic refuges be planted in each Bt cornfield; refuges allow Bt-susceptible beetles to develop without exposure to Bt toxins and are expected to mate with beetles from Bt corn. Mating beetles were hand-collected from refuge and Bt corn in fields planted as 20% structured, 5% structured, 5% seed blend and 0% refuge configurations. Mass and elytron length were recorded by sex; teneral status, spermatophore presence, sperm presence and ovary development were recorded for females.  Most mating pairs were collected near refuges. Mean male elytron length was greatest in refuge corn (3.89 ± 0.02 mm) and did not differ between seed blend and Bt-corn (3.79 ± 0.02 mm and 3.76 ± 0.02 mm, respectively). Mean female elytron length was also greatest in refuge (4.03 ± 0.02 mm) and did not differ between seed blend and Bt-corn (3.86 ± 0.02 mm and 3.85 ± 0.02 mm, respectively). Among females, 55.4% were teneral, and 93.6% had no observed ovary development. Spermatophores were found in the bursa copulatrix of 86.3% of females; 41.7% had sperm in their spermatheca. Among those with spermatophores, 96.4% had large spermatophores; 1.5% had mated multiply and contained two spermatophores. Beetle size was influenced by collection site corn type, but mating measurements were not. Females are mated soon after emergence, some mate multiply. Multiple mating may impact insect resistance management.