Accepted 24^th October, 2018

Four long-term field experiments were conducted on the impact of neonicotinoid pesticide (neonicotinoid) and organophosphate pesticide (organophosphate) on a honeybee colony in Japan. A few researchers in Japan assert that the chief culprit of a massive colony loss is not a neonicotinoid but an infestation of mites against our findings that a neonicotinoid would be deeply involved in the massive colony loss judging from the fact that mites and wax moth larvae cannot exist before colony extinction. We inferred from the field experiments in Japan that even when a colony does not collapse and looks active, a neonicotinoid can cause an egg-laying impediment of a queen and a decrease in immune strength of bees leading to the infestation of mites in a colony. In this work, we conducted a long-term (271 days) field experiment in Maui where there are neither mites harmful to honeybees nor distinct seasonal changes in organically-grown circumstances from October 22^nd 2014 to July 20^th 2015 with twelve colonies divided into four groups; each group consists of three colonies: a dinotefuran colony group where dinotefuran of 0.2 ppm was administered, a clothianidin colony group where clothianidin of 0.08 ppm was administered, a fenitrothion colony group where fenitrothion of 1 ppm was administered and finally, a control colony group where no pesticide was administered. These concentrations in the experiment conducted in Maui are same as those in the previous experiment conducted in Japan and are one-tenth of those in the other previous experiment. The results of the experiments in Japan where there are mites have been nearly duplicated on the experiment in Maui where there were no mites. In this work, the extinction ratios of neonicotinoid colony groups (dinotefuran and clothianidin) were 100% but those of both fenitrothion colony group and control colony group were 33.3%. From the long-term field experiments in both Japan and Maui, we can deduce the following conclusions: Neonicotinoid pesticides exterminate honeybee colonies with much higher probability than organophosphate pesticides which have the same extinction probability as control colonies have.

Key words: Dinotefuran, clothianidin, fenitrothion, neonicotinoid, organophosphate, sugar syrup, field experiment, long-term, pesticide, honeybee, Apis mellifera, colony, overwintering, colony extinction, collapse, acute toxicity, chronic toxicity, Maui, wintering, mite, mite-free, seasonless.