Integration of Bt Cotton in Ipm Systems: an Australian Perspective

Insect pests may have a severe impact on cotton production in Australia. Key pests are Helicoverpa spp which are well adapted to exploit cropping systems and often evolve resistance to pesticides. Until recently adoption of IPM has been restricted by a lack of nondisruptive tools. IPM must be founded on a thorough understanding of the ecology of pest and beneficial species, their interaction with the crop and surrounding non-crop environments. Insect resistant transgenic cottons have proved successful in providing a foundation for more sustainable, economically acceptable IPM with the integration of a range of other non-chemical tactics. In Australia, Bt cottons (tradename INGARD®) expressing the CryIAc endotoxin from Bacillus thuringiensis subsp. kurstaki, were commercialised in 1996/97 and gradually increased in area under an industry agreed deployment strategy which limited use to 30% of the cotton area. Two gene (Cry IAc/Cry 2Ab) varieties (Bollgard II) have been commercialised from 2004/05 and have now completely replaced Ingard varieties. All Bt varieties are grown under a comprehensive management strategy designed to minimise the risk of resistance evolving in Helicoverpa armigera, the main target pest. Commercial use of Ingard cotton varieties has reduced pesticide applications for Helicoverpa spp by 60%, providing major environmental benefits. Even greater pesticide reductions now occur with Bollgard II varieties. Pre-release environmental impact assessments demonstrated no significant effect of these Bt cottons on natural enemies. Commercial experience with Bt cotton crops has now shown a 3-4 fold increases in beneficial insect abundance compared to conventional crops. Co-incidentally several selective insecticides (indoxacarb, spinosad, and emamectin) became available for Helicoverpa control on conventional cotton, which further assisted in conserving beneficials. While resistance is the greatest risk for Bt