Is ‘pupae busting’ or destroying overwintering pupae of Helicoverpa spp. (Lepidoptera: Noctuidae) still relevant today in Australian Bt cotton?

Abstract

Transgenic Bt cotton was developed to control lepidopteran pests like the cotton bollworm, Helicoverpa armigera. However, there was concern that H. armigera would develop resistance to Bt cotton as this species had developed resistance to many insecticides and Bt toxins. To counter resistance, the cotton industry developed a resistance management plan (RMP) that included techniques to block resistant genes surviving from one season to the next (seasonal quarantining). One such technique is pupae busting, where cotton fields are cultivated after harvest, destroying potentially resistant pupating Helicoverpa spp. While pupae busting was important when there was only one insecticidal gene in Bt cotton, is it still relevant now Bt cotton has three insecticidal Bt genes? To address this question, we reviewed the development of pupae busting as a tool and its role in the current RMP. This included examining the ecology and behavioural characteristics of Helicoverpa spp. that impact on pupae busting efficacy (e.g., diapause, pupal mortality and pupae depth); the effect of soil type and different tillage techniques on pupae busting efficacy; and pupae busting within the context of Australia's current cotton farming system. We also looked at alternative forms of seasonal quarantining, such as using bisexual attract-and-kill techniques against adults. We confirmed that soil for pupae busting needs to be checked for moisture, which ideally should be less than the soil plastic limit. Comparisons between reports indicated that under good conditions, ‘go-devils’ and chisel ploughs were excellent pupae busters. While a bisexual attract-and-kill strategy of late season moths has a place within the industry, pupae busting is still the best method in seasonal quarantining and has a good fit within the modern cotton industry, particularly given differences in the biology and ecology of H. armigera and H. punctigera, and the presence of dominant resistance to Bt toxins by H. armigera in China.