Interaction of two Bacillus thuringiensis delta-endotoxins with the digestive system of Lygus hesperus.

The active-toxin form of CrylAc (65 kDa) or Cry2Ab was fed to a non-susceptible insect, Lygus hesperus, in an artificial diet. Biochemical and immunocytochemical methods were used to determine the distribution of ingested toxin. The toxins did not elicit a feeding deterrent response. CrylAc and Cry2Ab were ingested; small amounts were absorbed into the hemolymph as holoproteins, but most was excreted. SDS-PAGE analysis of CrylAc and Cry2Ab incubations with salivary gland homogenate showed a small decrease in the molecular weight of the active toxins. Proteolytic processing of the toxins also occurred in vivo, within the digestive system of L. hesperus. Excreted CrylAc and Cry2Ab retained activity toward lepidopteran larvae. Immunocytochemical in vivo localization studies showed negligible association of CrylAc with L. hesperus tissues. In contrast, strong extracellular association of Cry2Ab was observed with L. hesperus midgut brush border microvilli and basement membrane, as well as with cellular outlines within the hemolymph and fat body.