This study evaluates the effects of some insecticides on the survival of larvae of Apis mellifera L. The pyrethroids (fenvalerate and λ-cyhalothrin) caused maximum mortality at highest concentration (12.5 ppm), when compared to quinalphos and thiamethoxam. Fenvalerate was observed to be extremely toxic in its maximum concentration, as none among 1-2 days old treated larvae (after multiple exposures) survived after 24 hours (i.e., after 4^th exposure. Lavae were observed to be tolerant to thiamethoxam as 66.67% survival was observed till emergence under similar conditions.

Pesticide residues have been reported in hive-stored products for long periods. Larvae of honey bees experience oral or contact exposure to these products during their normal growth and development inside the cells. We analyzed various toxicological, morphogenic, and immunological effects of residue-based concentrations of two fungicides, captan and difenoconazole, on the larvae of worker honey bees, Apis mellifera. Selected concentrations (0.08, 0.4, 2, 10, and 50 ppm) of both fungicides were applied topically at a volume of 1 µL/larva/cell as single and multiple exposures. Our results revealed a continuous, concentration-dependent decrease in brood survival after 24 h of treatment to the capping and emergence stages. Compared to larvae with a single exposure, the multiply exposed youngest larvae were most sensitive to fungicidal toxicity. The larvae that survived higher concentrations, especially multiple exposures, showed several morphological defects at the adult stage. Moreover, difenoconazole-treated larvae showed a significantly decreased number of granulocytes after 1 h of treatment followed by an increase after 24 h of treatment. Thus, fungicidal contamination poses a great risk as the tested concentrations showed adverse effects on the survival, morphology, and immunity of larval honey bees.

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