Bt cotton has enabled the cotton industry to reduce its use of insecticides and improve the lifestyles of cotton growers by producing a more reliable and sustainable crop through controlling the major pests, Helicoverpa armigera and H.punctigera. However, unexpectedly high numbers of H. armigera and H. punctigera moths have been emerging from Bt cotton field tests, suggesting that about half the moths emerging from the cotton/refuge system could be originating from Bt cotton.

As the moths emerging from refuges do not appear to be overwhelming those emerging from Bt cotton, the above results indicate a potential weakness in the refuge strategy of the Resistance Management Plan (RMP). Consequently, we need to quantify the relative number of moth emergences from Bt cotton and refuges as Bollgard III is adopted, to test that our anti-resistance strategies are working with Bollgard III.

Given the apparently low numbers of moths emerging from refuges, other sources of susceptible moths, such as unstructured refuges, may be more important than previously expected. Researchers will measure the ability of some unstructured refuges to produce moths and therefore support the RMP.

From the RMP perspective, survival in Bollgard III is relative to survival in refuges, but refuge attractiveness & productivity is very variable, again compromising the refuge strategy. Here we aim to reduce refuge variability by calibrating moth emergence from well managed and poorly managed refuges.

Despite the higher than expected numbers of Helicoverpa emerging from Bt cotton, these moths were not resistant to Bt toxins. Instead, they apparently survived on poorly expressing flowers and bolls and therefore could have been tolerating low amounts of toxin. Work from CES 1304 indicated that the F2 generation of field caught moths tolerated proportionately higher levels of Cry1Ac toxin (c. 8x higher) than Cry2Ab toxin (NS) when compared to laboratory colonies. There was further evidence that moths emerging from Bt crops were particularly tolerant to Cry1Ac.

Although Bollgard III with Vip3A will reduce the resistance risk, both the expression of Vip3A and the resistance frequencies of Helicoverpa are less than ideal, so control via Cry1Ac & Cry2Ab remain crucial. Consequently, researchers will continue the work of CES 1304 to compare the level of resistance and amount of tolerance to Bt toxins in moths emerging from Bt crops and refuges.