ARS | Publication request: Update on monitoring of resistance to Bt cotton in key lepidopteran pests in the USA

Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: January 6, 2011
Publication Date: May 1, 2011
Citation: Dennehy, T.J., Carroll, M., Greenplate, J.T., Head, G.P., Moar, W., Price, P.A., Akbar, W., Akin, D.S., Bradley, J.R., Cook, D.R., Greene, J.K., Kerns, D., Leonard, B.R., Lopez, J., Roberts, P., Smith, R., Vanduyn, J., Unnithan, G.C. 2011. Update on monitoring of resistance to Bt cotton in key lepidopteran pests in the USA. Proceedings of the Beltwide Cotton Conferences. Paper 11502.

Interpretive Summary: Development of resistance in the tobacco budworm and bollworm to Bt toxins produced by widely-used transgenic cotton varieties continues to be a concern. The Environmental Protection Agency has mandated a large-scale Bt resistance monitoring program as an ongoing condition for approval of use of transgenic cotton throughout the Cotton Belt. As part of the Bt resistance monitoring program, bioassays of larvae collected from various cotton-growing areas during the 2010 growing season did not indicate development of resistance to two different Bt toxins in either species. Continued monitoring for Bt resistance development will be important because high variation in susceptibility of bollworm is being observed in the bioassays. Development of resistance in either the tobacco budworm or bollworm could have a major impact on the successful management of these two important pest species in cotton production throughout the Cotton Belt.

Technical Abstract: Producers sprayed more Bollgard II to control target lepidopteran pests in 2010 than in previous years, and therefore concerns have been expressed that the susceptibility of the target lepidopteran pests to the Bt Cry1Ac and Cry2Ab proteins in Bollgard II has significantly decreased. However, resistance monitoring of tobacco budworm, Heliothis virescens, and bollworm, Helicoverpa zea, for the 2010 cotton field season found no evidence of any change in susceptibility to either Cry1Ac or Cry2Ab in either of these target pests. As has been noted for bollworm in past monitoring results, there was continued evidence of high variation in susceptibility to both proteins, but no evidence that the level of variation has increased.