Effects of Bt Corn on the Development and Fecundity of Corn Earworm (Lepidoptera: Noctuidae)

Abstract

The corn earworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), is only moderately susceptible to most toxins from the bacterium Bacillus thuringiensis (Bt) expressed in transgenic corn. To better understand the impact of Bt corn on the life cycle of H. zea, we collected pupae of H. zea during 2014-2016 in North Carolina, South Carolina, and Mississippi from corn hybrids expressing Cry1Ab, Cry1F, Cry1F + Cry1Ab, Cry1F + Cry1Ab + Vip3Aa20, Cry1A.105 + Cry2Ab2, and Cry1A.105 + Cry2Ab2 + Cry1F, as well as from non-Bt near-isolines. We investigated the effect of Bt corn on pupal weight, fecundity, and egg viability of H. zea. Pupal weights were significantly reduced for males and females from all Bt hybrids compared with non-Bt near-isolines. Female pupae from the hybrid expressing Cry1F + Cry1Ab were also significantly lighter relative to those from the near-isolines expressing only Cry1F. Reductions in pupal weight did not result in any detectable effects on fecundity or egg viability. The reduction in pupal weight in the hybrids expressing Cry1F and Cry1F + Cry1Ab significantly declined over time in South Carolina, possibly indicating developing resistance to these Bt toxins. These data can be incorporated into insect resistance management models used to improve risk management decisions regarding H. zea in Bt crops in the complex landscapes of the southern United States.

Demographic Performance of Helicoverpa zea Populations on Dual and Triple-Gene Bt Cotton

“…In contrast, H. zea pupal weight varied when feeding on different cotton cultivars. Pupal weight is often correlated with fecundity [54], although this correlation might be affected by several other factors [55]. In our study, the heavier pupal weight was linked with higher fecundity, which agrees with reports for other noctuids, such as H. armigera [56].…”

Occurrence and Ear Damage of Helicoverpa zea on Transgenic Bacillus thuringiensis Maize in the Field in Texas, U.S. and Its Susceptibility to Vip3A Protein

“…Field bioassay data also showed that Vip3A technology could provide exceptional protection against H. zea damage [24,42,43,44]. High efficacy of Leptra maize expressing Cry1Ab, Cry1F, and Vip3A proteins against H. zea has been reported in several studies [44,45]. For example, Reay-Jones et al indicated that ear injury in Leptra maize, averaged across locations in the southern U.S., ranged from <0.01 cm 2 per ear in 2014 to 0.05 cm 2 per ear in 2012 [44].…”

Bt Resistance Implications for Helicoverpa zea (Lepidoptera: Noctuidae) Insecticide Resistance Management in the United States

“…The situation is similar for maize, with Bt hybrids now available that include the Vip3Aa20 toxin coupled with Cry1Ab, Cry1Ab + Cry1F, and Cry1A.105 + Cry1Ab2 lepidopteran-specific toxins. While the addition of the Vip3Aa toxin to existing cotton and maize pyramids will improve control of H. zea in the near term (Reay-Jones et al 2016, Little et al 2017, Bilbo et al 2018, the long-term effectiveness of the pyramid to delay resistance for Vip3Aa to H. zea will be reduced, because resistance to Cry1Ac + Cry1F, Cry1Ac + Cry2Ab2, Cry1Ab, Cry1Ab + Cry1F, and Cry1A.105 + Cry1Ab2 has already occurred (Dively et al 2016.…”

“…Although laboratory assays confirmed a baseline effective high dose, H. zea damage observations across a multi-year and state replicated experiment in a Cry1Ab + Cry1F + Vip3Aa20 maize hybrid found greater than expected damage (Reay-Jones et al 2016). In a follow-up study, pupae were recovered that had developed off this same Bt maize pyramid (Cry1Ab + Cry1F + Vip3Aa20; Bilbo et al 2018). Although contribution of viable offspring to the next generation has not been demonstrated at this time, the fact that larvae can survive long enough to cause measurable feeding injury in Vip3Aa maize and cotton and that pupae can develop from Vip3Aa20 maize is concerning.…”

“…Deeply engrained beliefs and practices are influenced only in part by the transfer of scientific information to the target audience. The importance of communicator credibility, the importance of group identity with the communicator, the importance of how the information is delivered to engender trust and membership of the community of the communicator and the target audience are demonstrated by many examples in the social sciences, including obesity reduction (Gray 1997, Gilson 2003, Bleich et al 2007 and beliefs surrounding climate change and evolution (Kahn 2015). Thus, university Extension personnel could make use of the trust and credibility they have with growers and focus more on techniques designed to foster a group identity among maize growers to increase planting of non-Bt structured refuge.…”