This project aimed to provide ecological information on an important pest species to underpin strategies for resistance management in Bt cotton. The cotton industry relies on Bt, now in Bollgard III® varieties, which provide security to growers, enable new farming systems and reduce pesticide use, ensuring continued social license to farm. At the time the project began, these benefits were threatened by rising frequencies of alleles giving resistance to Bt, especially to the Cry2Ab toxin in H. punctigera. Current resistance management plans were designed for H. armigera, but now they also had to consider H. punctigera. Updating our understanding of H. punctigera was therefore crucial. We needed to revisit key questions such as immigration from the remote inland, which was previously thought to be extensive and a valuable asset for resistance management, because it brought genes from unselected populations into cropping areas, thus diluting resistance.

For the previous three years, we had studied the ecology of H. punctigera in western Queensland, and compared results to the work we and others did in the 1980s and 90s. We had found that many remote inland areas still regularly produced many H. punctigera, but there was evidence of decreasing immigration to cropping areas. We speculated that the Millennium Drought of 2001 -2009 may have changed the distribution and abundance of key host plants, especially in mulga regions of western Queensland which act as a bridge to enable migration from the floodplains and sandy deserts of central Australia to cropping regions. However, in such a variable environment as inland Australia, we needed more data. This project aimed to provide better understanding of long term changes in H. punctigera populations that might affect pest impacts on cotton and other crops, and management of resistance to Bt in cotton.

We established ten pheromone trapping sites, six in western Queensland and four in non-cropping regions of South Australia, to monitor moth populations. Results showed fewer moths than before the Millennium Drought in parts of western Queensland, but substantial numbers in some South Australian sites, suggesting alternative migration routes from the inland. Eleven survey trips were made to inland regions, during which larval populations were sampled by sweep netting, and vegetation conditions and the presence of host plants were recorded. These results indicated a depletion of good host plants in the mulga regions since the drought, which probably contributed to reduced migration. We also studied diapause induction and termination and the timing of spring emergence in inland populations, and the potential for host plants with the C4 photosynthetic pathway to contribute to inland populations.

We added results from this project to data from earlier projects in a geographic information system which provides a long-term record that is unique in the study of insect pest ecology in Australia. The information will be crucial for the development of pest forecasting systems for a range of crops affected by H. punctigera. For cotton it has provided a long-term perspective of changes in resistance to Bt which indicates that increases in the frequency of resistance alleles in H. punctigera may occur from time to time due to prolonged droughts. However such increases are unlikely to be sustained, and the greatest resistance risk continues to be posed by Helicoverpa armigera rather than H. punctigera, because this species does not develop large populations in the inland.