Cytopathological action in mosquito larvae fed with Bacillus sphaericus (strain faiyoum) spore/crystal complex

Ingestion of Bacillus sphaericus (strain faiyoum) spore/crystal complex by larvae of Anopheles pharoensis, Culex pipiens and Aedes caspius was rapidly followed by a dissolution of the protein crystalline inclusions inside the anterior stomach of the three species. During the first day of the, B. sphaericus spores germinated within the mid-gut lumen, and were in a vegetative stage between 36-48 hours after ingestion when larvae began to die. Ultrastructural observations focused on larval mid-gut showed alterations, which differ according to the mosquito species, being localized mainly in the gastric caecae and posterior stomach. With the bacterial concentration used, neither general cell swelling nor complete breakdown of the mid-gut epithelium was recorded before larval death. In An. pharoensis larval mid-gut epithelium large low-electron-density areas appeared, rough endoplasmic reticula formed numerous concentrical structures and mitochondria swelled. Large vacuoles (of unknown origin) appear early in the Cx. pipiens mid-gut cells and rough endoplasmic reticula broke into small vesicles. Mid-gut epithelial cells of Ae. caspius showed mitochondria swelling except in the anterior stomach and a vacuolization of smooth reticula: these aspects remained unchanged until the larvae died.