This project was designed to support the deployment and continued use of transgenic (INGARD) cotton in the Australian cotton industry. To maximise the efficacy and useful lifespan of transgenic cotton we need to monitor the production of the toxin from Bacillus thuringiensis (Bt) in cotton plants throughout the growing season. Transgenic cotton contains a gene which encodes for the production of an insecticidal crystal protein (referred to as the &quote;toxin&quote;) which is highly toxic to Iepidopteran species including Helicoverpa, a major pest in the Australian cotton industry. These plants have been shown to successfully produce the toxin, but field studies indicated that the efficacy of plants was reduced later in the season (Fitt et al 1994). The cause of this reduced efficacy was not understood, although it is possible that production of the toxin is influenced by plant age or reproductive stage, and/or by a variety of environmental factors. Also, to ensure that resistance management strategies designed for use with transgenic cotton are successful, we need to assess the exposure of insects to the toxin.