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

Feeding experiments using the Bacillus thuringiensis delta-endotoxins, CryI A(c) and CryIIIA, were conducted with herbivorous insects from various orde rs (Lepidoptera, Coleoptera, Homoptera) in the laboratory. The mortality da ta obtained indicate a species-specific susceptibility of the insects to th e toxins whereby the feeding habits of the given animal seem to play a negl igible part. An unexpected, severely damaging effect of CryIIIA on caterpil lars was established, for the first time. By computing various development and nutritional indices it could be shown that retarded growth of the insec ts tested may not only be traced back to reduced feeding but also to a decr eased utilization of food containing an endotoxin. The insect gut seems to be the site of operation and of storage or complete degradation of the endo toxins because neither in the faeces nor in the haemolymph and fat body. co uld the toxins and their degradation products, respectively, be detected hi therto by means of gel electrophoreses. An altering effect of the toxins on the gut-microflora pattern is indicated from the first examinations but ha s to be further confirmed. Finally the applicability of these trials in cor responding examinations of transgenic plants producing B. thuringiensis tox in is dicussed.