In the mid-1990's the Australian cotton industry adopted Ingard®, a transgenic variety that contains a Bt toxin (CrylAc) which is specific to the group of insects including the target Helicoverpa armigera, but excluding natural predators and parasitoids of this pest. . In the 2004/05 season, Bollgard II® replaced Ingard as the transgenic variety of cotton available to Australian growers. It improves on Ingard® by incorporating an additional insecticide protein (Cry2Ab) to combat H armigera. In its first available season Bollgard II® was well adopted, with an average of 70% of the planted area throughout the industry.

·We know from artificial selection experiments in the laboratory that H armigera can develop Bt resistance. In addition, CSIRO Entomology has worked on resistance by natural populations of H armigera to transgenic cotton for many years, and presently maintains strains that are resistant to CrylAc or Cry2Ab. In both cases, the forms of genes (alleles) that confer resistance were isolated from field populations (CSE102C and CSE104C).

. To help prevent the development of Bt resistance in field populations of H armigera and thus prolong the utility of Bollgard II®, growers that use this tool must follow a resistance management plan (RMP). The RMP involves, in part, the growing of dedicated refuge crops aimed at producing sufficient Et-susceptible H armigera moths such that there is a high probability of them mating with resistant moths that may arise from the transgenic crop. The RMP is largely based on information from studies of the ecology and population genetics of H armigera, and the outputs of computer simulation models that use biological information to predict the likelihood of resistance developing under different scenarios. These models assume that any individuals which are resistant to the toxins in Bollgard II® survive to successfully reproduce in cotton landscapes.

However, natural enemies that frequent Bollgard II® crops may kill Bt resistant individuals. Such mortality is not represented in current models which predict the temporal aspects of development of resistance,. and is currently unquantified in the field. It would also be useful to know if such mortality differs between Bollgard II® crops and the common refuge crops (unsprayed conventional cotton, pigeon pea).

Some studies have characterized the arthropod fauna in fields of Bollgard II® versus sprayed conventional cotton. Bollgard II® crops are believed to contain a higher abundance and diversity of arthropods because broad-spectrum synthetic insecticides are not usually applied to this crop to control Helicoverpa. These arthropods include species that are natural enemies (predators or parasitoids) of a range of species including Helicoverpa. However they can also include secondary pests of cotton, such as mirids, which are controlled with synthetic

chemistries (e.g., Regent®) that also kill other sucking pests, thrips, and hymenoptera. Some of these arthropods include natural enemies of Helicoverpa (e.g., mirids attack eggs of Helicoverpa). Therefore, improved abundance and diversity of natural enemies in Bollgard II® fields may prevent Bt resistant larvae from reaching adulthood, but the frequency of use of synthetic insecticides to control secondary pests such as mirids might also affect this situation.