The Australian cotton industry has benefited greatly from the introduction of the transgenic Bolgard II cotton. Bolgard II expresses the Bt toxins which kill Helicoverpa larvae after feeding and has subsequently reduced the use of chemical insecticides to control insect pests. As resistance to the Bt toxins in Helicoverpa remains a threat, resistance managment plans for Bollgard II have been developed. These measures include, growing refuge crops to breed genetically suscpetible moths, pupae busting using cultivation to disrupt overwintering pupae in the soil and trap crops to retain the offspring of moths selected for Bt resistance.A limitation in evaluating these measures is that there has been no reliable way of determining whether trapped Helicoverpa adults are derived from larvae which were reared on cotton (and therefore exposed to Bt toxin), or on other crops such as pigeonpeas (widely used in refuge and trap crops). To address this shortcoming, we have reared moths on cotton and other host crops and then examined the adult moths for the presence of plant secondary metabolites. The secondary metabolites identified in moths were then correlated with the levels found in the different host plants.Extraction and analysis of n-alkanes in cotton and pigeon peas identified 15 linear alkanes and it was found that the relative abundance of hentriacontane and nonacosane in the plants was significantly different. Furthermore, a series of plant compounds, namely triterpenes and tocopherols were detected that were unique to cotton and pigeon peas. Moths reared on either conventional cotton, pigeon pea and other host crops were then analysed for the presence of these secondary metabolites. Alkane levels in the moths did not reflect the levels found in the plants indicating that the moths may biosynthesise their own alkanes. Tocopherols were identified and quantified in the moths and the levels found were an indicator of the plant on which the larvae fed.A series of other plant products were analysed in the moths and it is expected that using these biomarkers, along with the amount and type of tocopherol present, will allow for the determination of the larval host plant. The successful development of this assay will allow for the quantitative evaluation of resistance management plans by determining the host plant of adult moths.