H. armigera populations on cotton have been exposed to BT toxin from sprays and transgenic cotton for a number of years and a CRY 1Ac tolerant strain the “Silver strain” was bred by Dr HT Dang, from the survivors of the CRY 1Ac resistance monitoring programme. There has been some controversy over the CRY 1Ac resistance status of the “silver strain”. This controversy has been exacerbated by BT bioassay methods with a poor delivery of toxin to larvae and hence a poor dose response relationship. As this research project about the apparent ability of the “silver strain” to metabolise C RY 1Ac, is dependent on the assumption of resistance, we have done some research to improve BT bioassay methods and toxin delivery to the insect.