38th Annual Meeting of the Society for Invertebrate Pathology

The size and dominance of fitness costs associated with resistance have a large impact on the spread of resistance alleles. We used near-isogenic lines of Helicoverpa armigera to assess the nature of fitness costs associated with resistance to the Cry1A insecticidal proteins of Bacillus thuringiensis. Experiments were conducted with transgenic cotton producing Cry1Ac at two stages of development in which the level of expression was significantly different and on two crops that are offered as alternatives to cotton for the mandated refuges. First instar larvae of a resistant, a susceptible and the F₁ hybrid of these lines were placed individually on transgenic and conventional plants to assess their survival and development. The reproductive potential of the resulting adults was determined. These experiments showed significant variation in the nature of fitness costs associated with Cry1Ac resistance between cotton at different stages of maturity and between the conventional refuge plants. The implication of this variation for the use of refuges in resistance management will be discussed.