Toshiro Yamada¹*, Yasuhiro Yamada² and Kazuko Yamada<sup>1

1</sup>Division of Material Science, Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa, Japan.
²Department of Applied Physics, Graduate School of Engineering, University of Tokyo, Tokyo, Japan.
 

With exception of our previous study on a comparatively high pesticide-concentration level on the assumption that a pesticide is crop-dusted near an apiary there were no reports as regards the differences in the influence on a honeybee (Apis mellifera) colony between neonicotinoids and organophosphates. In this paper, the differences between neonicotinoids (dinotefuran and clothianidin) and organophosphates (fenitrothion and malathion) on a realistic pesticide-concentration level in the natural environment surrounding an apiary in Japan was investigated. The long-term field experiment was conducted from August 13^th 2013 to April 11^th 2014 (241 days). The colonies where the neonicotinoid was administered became extinct after assuming CCD aspect as was the case with our previous three long-term field experiments. It was shown that neonicotinoids can much more rapidly weaken the colony where it was administered than organophosphates and organophosphates can be rapidly degraded in honey stored as a result of their high degradability. These results roughly produced the findings in our previous experiment conducted at higher pesticide-concentrations than this experiment. Such a difference between neonicotinoids and organophosphates can exist in areas ranging from the vicinity of crop-dusted area to the natural environment. Analyzing the pesticide-concentration in residual honey in comb-cells, neonicotinoids whose concentrations in residual honey were lower than those in sugar syrup fed to each colony were detected but organophosphates were hardly detected. It was deduced from the analytical results that organophosphates are decomposed during storing of honey in comb-cells but neonicotinoids are hardly decomposed and that neonicotinoids can continue to be toxic in food (honey and pollen) stored while being diluted by pesticide-free nectar, pollen for a long period of time (during overwintering) and water in fields but organophosphates can rapidly become non-toxic, hence, making it possible for harmless food to be stored in combs. From our research it was inferred that obscure massive colony losses in winter can be probably caused by toxic food with a long-term persistent pesticide such as a neonicotinoid stored in combs during overwintering after the weakening of the colony due to the ingestion of toxic nectar, pollen and water under the natural circumstances contaminated by long-persistent pesticides such as neonicotinoids just before overwintering.

Key words: Dinotefuran, clothianidin, fenitrothion, malathion, neonicotinoid, organophosphate, realistic level, CCD, sugar syrup, field experiment, long-term pesticide, colony, residual concentration, honeybee, overwintering, colony extinction, collapse, acute toxicity, chronic toxicity, Apis mellifera.