Insecticide resistance in the cotton bollworm Helicoverpa armigera has been one of the greatest limitations to successful pest control and economic cotton production in Australia. The introduction of transgenic cotton has reduced the dependence on insecticides for control of this pest, however sprayed conventional (non Bt) cotton is still a viable cropping option in its own right as well as acting as a refuge for transgenic cotton. It is imperative therefore that resistance is monitored and managed to ensure insecticides remain an effective option now and in the future.

This research project focussed on the incidence and cause of insecticide resistance by Helicoverpa armigera and to a lesser extent H. punctigera. The objectives included continuing the insecticide resistance monitoring program for Helicoverpa spp., investigating resistance development within a Helicovpera spp. population, assessing the impact of AWM/IPM on resistance management, and formulating and promoting improved resistance management guidelines. Key findings include:

• Detection of low frequency resistance to the newer IPM compatible chemistries used against H. armigera including indoxacarb (Steward®) and emamectin benzoate (Affirm®).

• Indication that resistance to spinosad (Tracer®)and chlorfenapyr (Intrepid®) which had been increasing in previous years has decreased to low frequencies.

• Resistance is still present at variable frequencies in field populations to those chemistries that H. armigera are known to have developed resistance to, including endosulfan, pyrethroids, methomyl and organophosphates (profenofos).

• Very low frequency detection of resistance to endosulfan, pyrethroids and abamectin (Agrimec®)by H. punctigera in some valleys.

• Information recorded on species complex across time and space within cotton growing regions which has implications for the monitoring project and also for resistance management.

This information was used in assessment of current strategies and formulation of new strategies for managing insecticide resistance by the TIMS committee. The results and general resistance management tactics and information were promoted to the industry both verbally and written.

Various external factors inhibited effective analysis of the effects of AWM and IPM practises on resistance management. These included drought effects, low H. armigera pressure and high H. punctigera pressure resulting in several farms in the Macintyre Trial in 2003/04 and 2004/05 exiting the trial to use harder chemistry on this pressure.

Attempts to study resistance development to indoxacarb and emamectin benzoate, key IPM compatible chemistries about which little is know in regard to resistance, were unsuccessful. Problems encountered however have implications for resistance management, with further research to be undertaken.