Mode of Action of Bacillus thuringiensis δ-Endotoxin : Ultrastructural Changes of Midgut Epithelium of Pieris, Lymantria and Ephestia Larvae

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Abstract
A sequential observation of ultrastructural changes in the larval midgut of P. rapae, L. dispar and E. cautella following the administration of the crystals of B. thuringiensis was performed. Sequential changes which appeared in the columnar cells of the 3 spp. were the same as those seen in Bombyx and Galleria: Cells swelled becoming electron transparent and later burst in the apical portion. The nucleus was enlarged and endoplasmic reticulum assumed vacuole-like configuration. Disintegration of microvilli and deformation of the basal infoldings were characteristic. Only a change in mitochondria was not common to all. In Pieris (like Bombyx) most of the mitochondria were transformed into the condensed form, while in Lymantria and Ephestia they were retained intact (like Galleria). Two different changes among these species were observed in the goblet cells: enlargement of the intraspaces of the basal infoldings and condensation of the cytoplasm were characteristic to Pieris (like Bombyx)-which appeared weakly in Lymantria, while disintegration or disappearance of cytoplasmic projections lining the goblet cavity was observed in Lymantria and Ephestia (like Galleria) and in Pieris in a later stage. The changes which appeared in the goblet cells might reflect different distortions of ion balance among the species following the impact of .delta.-endotoxin.