Helicoverpa armigera is a major agricultural pest in Australasia. It has proven adept at developing resistance to all the synthetic chemical insecticides used against it, severely limiting the range of options available for its control. Of the insecticidal 8-endotoxins (Cry proteins) of Bacillus thuringiensis (Bt), the most effective against H. armigera is Cry1Ac. However with the advent of transgenic cotton expressing Cry1Ac, there is a greatly increased risk of H. armigera developing resistance to Cry1Ac due to increased selection pressure. In our laboratory we have selected a line of Cry1Ac-resistant H. armigera, demonstrating that genes for resistance already exist in wild populations. There is therefore an urgent need for new insecticides to control H. armigera. We are taking several approaches to identifying new insecticidal proteins that can be used for this purpose, and one of these is to test a range of modified Cry toxins constructed by domain swapping. Cry toxins are produced in the form of a protoxin that is cleaved by proteases in the insect gut to produce the active form. The activated toxin has a three-domain structure in which domain I is recognised as the domain responsible for pore formation, while domains II and III are involved in receptor recognition and binding. By interchanging the individual domains from different members of the Cry protein family chimeric proteins with altered specificity or toxicity can be produced. We have tested a range of chimeric proteins by bioassay to measure their toxicity towards H. armigera. [Texte intégral]