Summary — Newly emerged adult workers of Apis mellifera and A cerana indica tolerated a topically applied dose of 100 μg diflubenzuron (DF) and penfluron (PF) in acetone but the treated bees weighed less than control bees at 2 and 6 d of age. Oral administration of 100 μg DF (as Dimilin 25% wettable powder) in 10 μl sugar syrup proved fatal to A c indica. After 6 d of feeding 50 μg DF, hypopharyngeal gland development, measured as size of acini, was significantly suppressed in both bee species. The suppressed gland development in the treated group could be a consequence of poor gain in weight. Foragers of both bee species readily accepted DF-contaminated sugar syrup and, with increasing doses, there was decrease in time required to consume the contaminated sugar syrup in a dose-dependent manner. The treated bees weighed significantly less than the control bees. Thus, at higher doses chitin synthesis inhibitors may also prove harmful to adult bees.

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Summary — Diflubenzuron (DF) and penfluron (PF) in acetone were found to be equally toxic to Apis mellifera and A cerana indica in topical application tests based on equivalent body weights. Toxicity resulting from median lethal dosage was highest for pupae and was lower for IV and III instar larvae. Acetone proved lethal to eggs, I and II instar larvae. There was no delayed lethal and morphological effect of the treatment on larvae, but some adult bees, treated in the same manner as pupae, showed morphological abnormalities, such as crumpled wings and poor interlocking at stylet and lancets of the sting apparatus. Feeding of 50 mg DF to small experimental colonies of both bee species enhanced egg laying but significantly reduced the amount of unsealed and sealed brood within 10 days of treatment.Apis mellifera / Apis cerana / diflubenzuron / penfluron / median lethal dose / toxicity / pesticide

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