The Ecology of 'Helicoverpa Punctigera': Adaptations for a Changeable Climate

Abstract

The native budworm 'Helicoverpa punctigera' is an important pest of field crops in Australia alongside the cotton bollworm 'Helicoverpa armigera', and both share a number of host plants. 'H. punctigera' moths are known to migrate into cropping regions, from inland Queensland, Western Australia and South Australia but multi-year weather perturbations such as the Millennium drought may have reduced migration from drought-stricken areas in inland Queensland. Resistance management in Bt cotton may be at risk from reduced migration as migrants dilute any resistance genes that might be present in 'H. punctigera' that have been exposed to Bt toxins. In southeast Australia 'H. punctigera' appears to be becoming more abundant later in the cotton growing season, and thus, the overwintering ecology of 'H. punctigera' needs to be re-examined. Laboratory studies were conducted under a range of temperatures and photoperiods to determine under what conditions diapause occurs in 'H. punctigera', and to compare the results with similar published studies. At 25°C the least amount of diapause was induced at 14L:10D, and the highest percentage of diapause at 12L:12D. Temperatures of a constant 19°C or cooler produced the highest percentages of diapause, even under a summer 14L:10D photoperiod. At 12L:12D photoperiod the highest percentages of diapause were induced at temperatures below 19°C. Larvae and pupae moved from 25°C to 19°C showed an increase in diapause levels while larvae moved from 19°C to 25°C did not. A statistical model was created from my data, showing the significant effects of temperature, photoperiod, and photoperiod-temperature interaction on diapause induction.