Toxicity of dietary avidin and streptavidin to the cowpea bruchid, Callosobruchus maculatus (F.)

Avidin, a large protein from egg whites, powerfully binds biotin, a vitamin for many insects. When avidin was incorporated into the diets of larval Callosobruchus maculatus (F.), the cowpea bruchid, at relatively low levels (10–30 ppm), there was a marked dose-dependent increase in mortality, as well as a small increase in the developmental time of survivors. Avidin toxicity was prevented when biotin was added to the diet together with avidin. Sub-lethal doses of avidin caused reductions in fecundity. Avidin had no effect on the larval feeding rates during the first three instars, even when the larvae were consuming amounts of the protein that would later cause death. In the fourth instar there was a dose-dependent reduction in the rates of feeding as the avidin level in the food increased. Death of the C. maculatus larvae usually occurred at the pupal/adult stage still within the host seed. Streptavidin, a biotin-binding protein from a bacterial source, had effects similar to chicken egg avidin.