The silverleaf whitefly (SLW) Bemisia tabaci B-biotype is a major problem to cotton growers overseas and is a threat to the cotton industry in Australia. It is currently established in plant nurseries in most states and is a pest of various horticultural crops in the field in North Queensland. The genetically modified INGARD cotton contains a Bt gene which codes for an endotoxin that is active against major lepidopteran pests such as Helicoverpa spp. Bt cotton has been trailed in Australia over the last few years with some positive results (D. Murray pers. comm. ). However, the key to the success of transgenic cotton will be to integrate it with other management strategies, such as crop refuges, in an effort to slow resistance development (Fitt 1996). Pigeon pea is highly preferred by Helicoverpa spp. and is being used as a refuge or trap crop (Walker et al 1998). Lucerne is also being investigated as a refuge or breeding ground for beneficial insects (Mensah & Singleton 1998; Walker et al 1998), such as predators or parasites of Helicoverpa spp. Sowthistle, a common weed in cotton agro ecosystems, may also act as a refuge for beneficial insects or for the pests themselves. Cotton and lucerne are both hosts of the SLW overseas. These and other plants in the cotton agro ecosystem may become important hosts in Australia. This project assessed the suitability of these key hosts to SLW development.