Mode of Action of Bacillus thuringiensis δ-Endotoxin : Effect on Galleria mellonella (Lepidoptera : Pyralidae)

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Abstract
The general pathology of G. mellonella induced by B. thuringiensis .delta.-endotoxin was studied in terms of symptoms, relative roles of crystals and spores, hemolymph chemistry and the associated histopathology of the midgut. Bioassay using pure crystals and spores demonstrated that the primary cause of death of Galleria larvae was the crystals and the presence of spores was supplemented. Four h after 1 administration of crystals, changes appearing in the columnar cells of midgut epithelium were similar to those observed in completely paralyzed B. mori; cells swelled losing their microvilli, burst or sloughed off into the lumen. Changes appearing in the goblet cells differed from those observed in B. mori; mitochondria came out from cytoplasmic projections which diminished in number in some cells. When cells sloughed off from the basement lamina, the projections were totally deformed. Mitosis and development of new columnar and goblet cells to replace the broken cells were more frequently observed in the regenerative cell-masses (nidi) than in those of normal epithelium. Although blood pH scarcely changed, the K+ level rose up to 1.3 times. The reaction of G. mellonella to serotype VII is not that of a type III host species.