Transgenic (Bt) cotton varieties provide a substantial basis for economically and environmentally sustainable insect pest management within the Australian cotton industry. The introduction of Bt cotton has significantly reduced pesticide use for the control of key pests such as Helicoverpa spp. and encouraged a greater emphasis on the management of beneficial invertebrates in pest control. A major risk now facing the cotton industry, from a pest management perspective, is the development within H. armigera of resistance to Bt. As a result, mandatory requirements are placed on growers of Bt cotton to provide refuge crops (no Bt exposure) as sources of susceptible moths that will mate with any potentially resistant moths arising from the Bt crops – thus swamping resistance development. Various refuge crops are available as options (pigeon pea, maize, sorghum, conventional cotton). To properly evaluate the utility of such refuges, we need improved knowledge of the degree to which moths generated by them and those emerging from Bt crops effectively mate. A core assumption of the current Bt Resistance Management Plan for Bt cotton is that moths from different crop origins mate at random. Using carbon isotope signatures characteristic of C3 and C4 plants (e.g. cotton and pigeon pea cf maize and sorghum), this project demonstrated that mixed matings of Helicoverpa moths from such different plant host origins can be common on the landscape, but the assumption of random mating in such instances may not strictly be true. More research is planned to further confirm these conclusions.

This project also continued monitoring of long-term (and seasonal) changes in Helicoverpa abundance in cotton growing regions through networks of pheromone trapping in the Namoi Valley and St George / Dirranbandi regions that began prior to the introduction of Bt cotton. The pheromone trap catches for H. armigera in the Namoi Valley suggested this species has increased in abundance (at landscape scale), especially late in the cotton growing season, since the advent of Bt cotton. The mechanisms driving such change are not understood, but could be related to reductions in pesticide use and / or concurrent variations in the use of other crops on the landscape that are attractive to the moth. The abundance of H. punctigera has also increased in the last few years. Spring surveys of crops, weeds and native vegetation showed promise as early warning indicators of the forthcoming seasonal bias in Helicoverpa spp. in cotton crops.

Concurrent with our work on Helicoverpa, we opportunistically gathered data on the abundance of secondary cotton pests and beneficial invertebrates within refuge crops and their associated Bt cotton crops. Refuge crops (especially pigeon pea crops which were the focus of much of the work done in this project) supported substantial populations of mirids and predatory beetles and bugs. The balance of effect of such pests and beneficial species for cotton production needs further study with respect to movements to cotton crops and the hindrances beneficial species may provide to effective Helicoverpa production within refuges.

In addition, we explored the potential of jasmonic acid, a chemical involved in plant response to herbivore damage, to act as an attractant for beneficial invertebrates in cotton crops. Such responses have been suggested by overseas research. Identification of attractants for beneficial species could provide useful tools to enhance IPM in Australian cotton systems. However, jasmonic acid failed to influence aggregative behaviour of beneficial invertebrates in trials we conducted in conventional cotton fields.