The histopathological effects of Bacillus thuringiensis subsp. kurstaki δ-endotoxin on the Malpighian tubule cells of Pieris canidia larva were studied after mucosal and serosal treatment. Results showed that tissues examined after one minute of exposure to the toxin had already undergone fine structural alterations. The number of vacuoles in the cytoplasm increased, and the apical microvilli and the basal intracellular channels became slightly disorganized. The mitochondria, however, appeared normal. After ten minutes of toxin treatment, the ground cytoplasm had large vacuoles or cytoplasmic spaces, the microvilli were damaged extensively, there was extrusion of apical cytoplasm, and the basal infoldings were damaged. After twenty minutes of toxin treatment general cell disintegration was observed. The microvilli were severely damaged, the apical membrane lysed, all the mitochondria became very swollen, the rough endoplasmic reticula and cytoplasm were extremely vacuolated, the basal infoldings were greatly disorganized, and the basement membrane was eroded. These results indicate that Bacillus thuringiensis δ-endotoxin could effect cell leakage by forming large pores in cell membranes.
Bacteria, Insect excretory system, Ultrastructure
