Mortality of western corn rootworm larvae on MIR604 transgenic maize roots: field survivorship has no significant impact on survivorship of F1 progeny on MIR604.

Mortality of western corn rootworm, Diabrotica virgifera virgifera LeConte, larvae due to MIR604 transgenic corn, Zea mays L., expressing the modified Cry3A (mCry3A) protein relative to survivorship on corn with the same genetic background without the gene (isoline corn) was evaluated at three Missouri sites in both 2005 and 2006. We made these comparisons by using wild-type western corn rootworm at three different egg densities (6,000, 3,000, and 1,500 eggs per m) so that the role of density-dependent mortality would be known. The mortality due to the mCry3A protein was 94.88% when averaged across all environments and both years. Fifty percent emergence of beetles was delayed approximately 5.5 d. Beetles were kept alive and their progeny evaluated on MIR604 and isoline corn in the greenhouse to determine whether survivorship on MIR604 in the field for one generation increased survivorship on MIR604 in the greenhouse in the subsequent generation. There was no significant difference in survivorship on MIR604 in greenhouse assays between larvae whose parents survived isoline and larvae whose parents survived MIR604 in the field the previous generation, indicating that many susceptible beetles survived MIR604 in the field the previous season along with any potentially resistant beetles. The data are discussed in terms of rootworm insect resistance management.

Native resistance to western corn rootworm (Coleoptera: Chrysomelidae) larval feeding: characterization and mechanisms.

Seven maize, Zea mays L., genotypes selected for native resistance to western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), larval feeding damage (SUM2068, SUM2162, CRW3(S1)C6, NSS1 x CRW3(S1)C6, PI583927, CRW2(C5), and AR17056-16) were evaluated along with three control maize genotypes in the field for plant damage, larval recovery, adult emergence, root size, and root regrowth. Larvae recovered were further analyzed for head capsule width and dry weight and adults for dry weight. All factors evaluated with the exception of adult dry weight varied significantly among maize genotypes. Control genotypes included a highly susceptible hybrid, B37 x H84, a transgenic rootworm-resistant hybrid expressing the modified Cry3A protein (MIR604), and the untransformed modern hybrid with the same genetic background as the MIR604 we used (isoline) as a second susceptible control. In general, the genotypes previously selected for resistance to western corn rootworm larval feeding had less damage, fewer larvae recovered, smaller larvae recovered, and fewer adults recovered than the susceptible controls. SUM2162 was significantly less damaged than all other native sources of resistance. Western corn rootworm larvae recovered from SUM2162 and SUM2068 were significantly smaller in terms of head capsule width and average weight than larvae recovered from all other maize genotypes, indicating that antibiosis is a mechanism of resistance for these two hybrids.

Impact of MON863 transgenic roots is equivalent on western corn rootworm larvae for a wide range of maize phenologies.

The effects of maize, Zea mays L., phenology on establishment, damage, and adult emergence of the western corn rootworm, Diabrotica virgifera virgifera LeConte, on MON863 transgenic maize expressing the Cry3Bb1 protein and its isoline was evaluated in field trials in 2002 and 2003. As expected, plant damage, western corn rootworm larval recovery, and adult emergence were significantly lower on MON863 than isoline maize. The average weight of larvae and adults recovered from MON863 and isoline maize was generally not significantly different. If western corn rootworm larvae were able to establish on transgenic rootworm-resistant plants, larval growth was relatively normal. Plant damage, the number of western corn rootworm larvae recovered, and adult emergence from MON863 did not significantly differ between egg hatch times from widely varying phenologies in either year of the study. Although the extractable level of Cry3Bb1 decreased significantly from vegetative (V)4 to V9 maize in previous studies, in the current study, the amount of Cry3Bb1 did not vary from V3 to R3 in a way that affected neonate survival by western corn rootworm larvae in the field.