Insecticide resistance represents one of the most significant limitations to successful pest control and economic production in Australian cotton industry. This project has continued a long-term resistance monitoring program for Helicoverpa armigera and H. punctigera for three seasons from 2008 to 2011. Other aspects of the project include cross-resistance and resistance mechanism research, accumulation of dose response data for new insecticides and resistance management formulation and promotion.

Insecticide resistance monitoring was conducted in 2008/09, 2009/10 and 2010/11. The objective of the monitoring program was to detect resistance to conventional insecticidal chemistries used for control of Helicoverpa species and monitor trends and changes in resistance frequency. Conclusions from monitoring were:

*Very low resistance frequencies detected to the IPM compatible chemistries of indoxacarb, spinosad, emamectin benzoate and rynaxypyr.

* Resistance remains present but stable in field populations of H. armigera to chemistries that this species has developed resistance to in the past, including endosulfan and methomyl

* Widespread general pyrethroid resistance remains present in H. armigera populations as indicated by high resistance frequencies to fenvalerate. However resistance to bifenthrin is low and low and relatively stable.

* Very low level resistance to endosulfan, pyrethroids and abamectin in H. punctigera.

These results have direct implications for insecticide use within the cotton, grain and pulse industries. They indicate that effective control of Helicoverpa will continue to be provided by the IPM compatible insecticides utilised by these industries. Studies of cross-resistance conducted in this project demonstrate a lack of cross-resistance between these chemistries and Bt toxins which also gives confidence that efficacy will not be compromised by the high uptake of Bollgard II by the Australian cotton industry. Nevertheless, detectable resistance to these compounds, albeit at very levels, highlights the importance that insecticides continue to be used within the IRMS and that they continued to be monitored to ensure that their effectiveness is retained, particularly if their overall use increases.

The observed stabilisation of resistance to older insecticides is consistent a reduction in selection pressure associated with declines in insecticide use since the introduction of Bollgard II.

Comparison of the sequence of one esterase from pyrethroid resistant and susceptible larvae suggested a possible role in resistance for this esterase, with several point mutations between the S and R strain coding for different amino acids. Studies such as this are part of building an overall picture of resistance and the mechanisms behind it, and provide the basis for further investigation.

In addition to resistance monitoring and mechanism research for chemicals currently registered for use on cotton, it is essential that baseline responses be established for new chemistries prior to registration. Following on from similar work in establishing discriminating dose bioassays for rynaxypyr, a pilot study for determining the dose-response of a chemically similar anthranilic diamide, cyazypyr was undertaken. This enables early detection of resistance development in populations before it is evident in the field and allows appropriate management responses to be activated in order to minimise future resistance risk.The final aspect of this research is the formulation and promotion of resistance management strategies and principles. The assessment and formulation of the IRMS by TIMS has utilised resistance monitoring data which has enabled changes to be made to the IRMS at the request of the industry.