Histopathological alterations in alimentary canal of Periplanata americana induced by oral administration of cypermethrin, carbaryl and monocrotophos

Oral administration of sublethal dose (less than the LD₅₀ value for 96 hours) of cypermethrin (2.0x10⁻³ mg), carbaryl (5.0x10⁻² mg) and monocrotophos (1.8x10⁻¹ mg) for 96 hours induced noticeable changes in the alimentary canal of Periplanata americana. Histolopathological changes due to insecticide treatments in foregut include contraction of the circular muscles with air spaces around them, breakdown in continuity of circular muscle, detachment of longitudinal muscles from the epithelium and shrinkage in epithelial lining cells along with the nuclei. The changes observed in midgut of the exposed cockroaches were the detachment of longitudinal muscle and shrinkage of circular muscles, shrinkage of the columnar cells along with nuclei, fusion of columnar epithelial cells, evacuation of the nuclei, vacuolization of cytoplasm and loss of cytoplasmic density and organization. Of the three insecticides tested, carbaryl treatment elicited more severe changes in the alimentary canal as compared to the other insecticides. In case of carbaryl treatment, the cell membranes were completely destroyed and cytoplasm was evacuated into the lumen leaving behind the nucleus and excessive vacuolization of the epithelial cells. The intima secreted by the epithelial cells was destroyed at most of the places after carbaryl treatment but remained unaffected under cypermethrin and monocrotophos ingestion. The present study reveals that the alimentary canal is grossly affected by insecticides and might be one of the factors contributing to death of the cockroaches.