The Resistance Management Plan (RMP) for Australian Bt cotton aims to minimise the development of resistant Helicoverpa moths. This project aims to assess if the legislated distance between pigeon pea and Bt legislated in the plan is adequate for preventing the movement of larvae between crops on commercial farms. To do this the behaviour and movement of larvae was observed. An experiment was set up to test how the movement of larvae was affected by factors such as the distance between pigeon pea and cotton (25 - 100cm), crop attractiveness (cotton either had or did not have flowers) and the presence of water. The experiments showed that larvae will move up to one metre over bare soil to reach Bt cotton. Furthermore, the likelihood of larvae reaching the cotton is increased by the presence of cotton flowers. Larvae were also observed swimming on water suggesting that this is a way in which young Helicoverpa can move within the field. This information indicates that, to improve the efficiency of the current RMP refuges should not be adjacent to Bt cotton within the same field but future work is needed to validate these laboratory findings under field conditions.

Helicoverpa armigera and Helicoverpa punctigera are destructive and adaptable pests that co-exist within the Australian cotton industry. There has been minimal research regarding how these two species interact within cotton crops to understand if one species dominants the other, or in which environment this dominance occurs. As part of the RMP, refuges are planted next to Bt cotton to produce high numbers of moths. If larval numbers are high in these refuges, then one Helicoverpa species could force out the other onto the neighbouring Bt cotton, where it would be exposed to Bt toxins. The aim of this work was to establish how H. armigera and H. punctigera competed for food, and whether in times of high density, one species was more likely to be pushed out of the pigeon pea into Bt cotton. Mixed and single species groups of 3rd to 5th instar H. armigera and H. punctigera larvae were set up on non-flowering pigeon pea or flowering non-Bt cotton refuges, and given the option of moving onto Bt cotton. H. armigera were likely to move off non- flowering pigeon pea irrespective of larval density. In mixed species groups, H. armigera and H. punctigera behaved as if they are one species complex and neither were more likely to move off the non-Bt flowering refuge. Both larvae species also seemed to be gregarious, but this needs further investigation. These results indicate that interspecific competition will not cause one species to be more exposed to Bt cotton than the other, but that there may be differences between the species in whether they will move onto Bt cotton.