Assessment of the antimetabolic effects of trypsin inhibitors from cowpea (<i>Vigna unguiculata</i>) and other legumes on development of the bruchid beetle <i>Callosobruchus maculatus</i>

Abstract

Abstract Insect feeding trials were carried out whereby cowpea trypsin inhibitor (CPTI) was incorporated at various levels up to 10% in pelleted meals of both a susceptible variety of cowpea and another susceptible species of legume, the chickpea. The results confirmed that CPTI, prepared by affinity chromatography, is an effective antimetabolite against C. maculatus; furthermore, it is also effective when added to pelleted chickpea meals. Bioassays using soya bean trypsin inhibitor (SBTI) and lima bean trypsin inhibitor (LBTI) showed these protease inhibitors to be relatively ineffective. Methionine supplementation of meals of resistant cowpea resulted in increased adult survival from approximately 43 to 89% relative to the controls; addition of cysteine had a similar effect. Supplementation with both methionine and tryptophan, probably the next limiting amino acid in cowpea, did not increase adult survival any further. It is concluded that CPTI is an effective antimetabolite of C. maculatus and that this type of mechanism may be widespread. However, it relies upon a finely controlled balance within the host plant which has to make available sufficient nutrients for itself but insufficient to maintain predation since this example of resistance can be overcome by by‐passing the limiting sulphur amino‐acid block.