Effects of Bacillus thuringiensis δ-endotoxins on food utilization, growth, and survival of selected phytophagous insects

Feeding experiments using the Bacillus thuringiensis delta-endotoxins, CryIA(c) and CryIIIA, were conducted with herbivorous insects from various orders (Lepidoptera, Coleoptera, Homoptera) in the laboratory. The mortality data obtained indicate a species-specific susceptibility of the insects to the toxins whereby the feeding habits of the given animal seem to play a negligible part. An unexpected, severely damaging effect of CryIIIA on caterpillars was established, for the first time. By computing various development and nutritional indices it could be shown that retarded growth of the insects tested may not only be traced back to reduced feeding but also to a decreased utilization of food containing an endotoxin. The insect gut seems to be the site of operation and of storage or complete degradation of the endotoxins because neither in the faeces nor in the haemolymph and fat body. could the toxins and their degradation products, respectively, be detected hitherto by means of gel electrophoreses. An altering effect of the toxins on the gut-microflora pattern is indicated from the first examinations but has to be further confirmed. Finally the applicability of these trials in corresponding examinations of transgenic plants producing B. thuringiensis toxin is dicussed.