Mode of Action of Bacillus thuringiensis δ-Endotoxin : Changes in Hemolymph pH and Ions of Pieris, Lymantria and Ephestia Larvae

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Abstract
The general pathology in terms of larval behavior and hemolymph physiology following the administration of Bacillus thuringiensis δ-endotoxin was studied on the so-called Type II insects, Pieris rapae, Lymantria dispar and Ephestia cautella.After the impact of the toxin, larvae of the three species stopped feeding and died in 2-7 days. Pieris became gradually sluggish, suffering from vomiting and diarrhea, while Lymantria and Ephestia looked normal except for occasional vomiting and diarrhea in the former.When the columnar cells of midgut epithelium showed the obvious histopathological changes corresponding to those of the paralyzed Bombyx, hemolymph pH changed from 6.8 to 7.4 accompanied by a rise in K+ level up to 2 times that of the normal hemolymph in Pieris. On the other hand, in both Lymantria and Ephestia there was no change of pH and rises of K+ levels of 1.4 times in Lymantria and 1.1 times in Ephestia were observed. Thus, the degree of rise in the pH and K+ concentration of hemolymph seemed to be associated with intensities of symptoms as weel as cytoplasmic condensation which appeared in the goblet cells as follows : Bombyx>Pieris>Lymantria>Galleria≥Ephestia.