Resistance research and monitoring to enhance stewardship of Bt cotton and management of Helicoverpa spp.

This project continued a long-term program monitoring resistance in field populations of Helicoverpa spp. to enable the industry to respond to emerging issues related to Bt resistance. During 2017/18, F1 screens were used to assess populations of H. armigera and H. punctigera with no increase being found, over time, in the frequencies of resistance to Cry1Ac, Cry2Ab and Vip3A. F2 screens found no dominant forms of Bt resistance but did detect a new recessive Vip3A resistance in H. armigera. There is no indication from the characterisation work that a novel variant of Cry2Ab resistant H. armigera poses a different threat to that of the first isolated variant.

The project also considered whether multiple resistance to Bt toxins in Helicoverpa spp. poses a threat to 3-gene cotton. Laboratory bioassays demonstrated that it is possible to select for Cry1Ac resistance in a Cry2Ab / Vip3A background, however, field experiments suggest the existence of a fitness cost that results in the death of most larvae.