Neonicotinoides are long-persistent and highly toxic pesticides that have become popular instead of organophosphates and are strongly suspected to cause massive disappearance of bees. On the other hand, the evaluation of a long-term influence of a pesticide on a honeybee colony in the natural environment is not yet established. In this paper, we conducted a long-term field experiment and found different impacts on honeybee colonies (Apis mellifera) in an apiary between the neonicotinoid dinotefuran and the organophosphate fenitrothion. Each concentration of the pesticides in sugar syrup provided for honeybees was adjusted at the same insecticidal activity to exterminate stinkbugs. The colony where dinotefran was administered (dinotefuran colony) became extinct in the administration period of 26 days, while the colony where fenitrothion was administered (fenitrothion colony) survived long after the same administration period. The fenitrothion colony succeeded in overwintering and staying alive for more than 293 days after administration, which seems to be able to recover even after the exposure to fenitrothion. The dinotefuran colony became extinct though the intake of dinotefuran was estimated to be comparable with that of fenitrothion in terms of the LD50 to a honeybee. Judging from the results in this work and our previous works, we speculate that colonies exposed to dinotefuran hardly recover from the damage because dinotefuran has a much longer persistent ability than fenitrothion and toxic foods stored in cells over a prolonged period of time can affect a colony.

Key words: Dinotefuran, neonicotinoid, fenitrothion, organophosphate, CCD, sugar syrup, field experiment, long-term, pesticide, honeybee, colony, overwintering, colony distinction, acute toxicity, chronic toxicity, Apis mellifera.