The concentration-mortality response of third instar larvae of Chrysomya megacephala (Diptera: Calliphoridae) to a synthetic insecticide, imidacloprid, and its impact on histopathological, histochemical, and biochemical parameters were determined in laboratory assays. Larvae displayed a concentration and time-dependent mortality response for the insecticide. Histopathological studies exhibited quite noticeable modifications in the epithelial cells, peritrophic membrane, basement membrane and muscular layer of the larval midgut. The ultrastructural analysis demonstrated alterations in nuclei, lipid spheres, microvilli, mitochondria, rough endoplasmic reticulum and lysosomes. In addition, histochemical tests on the midgut were performed, which revealed a strong reaction for proteins and carbohydrates in the control group and a weak reaction in the group exposed to imidacloprid in a dose and time-dependent manner. Imidacloprid also caused a significant reduction in the total midgut content of carbohydrates, proteins, lipids and cholesterol. Larvae treated with imidacloprid also showed a reduction in the activities of acid and alkaline phosphatases at all concentrations compared to untreated larvae.
Keywords: acid and alkaline phosphatases; histochemistry; insecticide; nutritional parameters; toxicity; ultrastructure.
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