| Transgenic corn and cotton expressing crystalline (Cry) insecticidal proteins from Bacillus thuringiensis (Bt) were commercially introduced in 1996. This technology has greatly improved the control of several key lepidopteran insect pests tobacco budworm, Heliothis virescens (Farbricius), pink bollworm, Pectinophora gossypiella (Saunders), southwestern corn borer, Diatraea grandiosella (Dyar), and European corn borer, Ostrinia nubilalis (Hubner). The corn earworm, Helicoverpa zea, has been more difficult to control using Bt crops and supplemental insecticide applications are often needed to prevent economic losses. A major threat to the longevity of transgenic technology is the evolution of resistance, especially when an insect pest infests both Bt corn and cotton in the same growing season. Similar Cry proteins are currently expressed in both corn and cotton commercial production systems. At least one generation per year develops on Bt corn before infesting cotton. Given that H. zea infests both crop hosts at some point every year, the objectives of this study were to evaluate the contribution and influence of Genuity VT3 PRO corn (expressing Cry1A.105 and Cry2Ab) on H. zea density, fitness, and selection on BollGard II cotton (expressing Cry1Ac and Cry2Ab). Non-Bt and VT3 PRO corn fields were sampled for larval density and any observed larvae were collected. Non-Bt field corn supported 61% more larvae compared to VT3 PRO fields. Larvae infesting non-Bt corn developed faster than those infesting VT3 PRO corn. Larvae collected from VT3 PRO corn had significantly higher pupal weight two out of the three years of this study. Pupae from VT3 PRO corn also had longer pupal duration two out of three years compared to pupae of larvae collected from non-Bt corn. Offspring from larvae reared on VT3 PRO corn had a higher LC50 compared to offspring from larvae reared on non-Bt corn. H. zea susceptibility to Bt is highly variable but the results presented here indicate that dual-gene corn hybrids such as VT3 PRO can select for H. zea populations with a higher propensity for causing damage in Bt cotton. |
