Assessment of sensitivity level of honeybee (Apis mellifera) to neonicotinoid insecticides

Declining population of honeybee day by day is the major threat, and this decline is due to variety of stressors. As honeybees are considered most important pollinators of our managed and wild corps, we investigated the effect of neonicotinoids; acetamiprid, imidacloprid, thiacloprid and clothianidin on honeybees by ingestion and contact method. Finding of this study showed that among these neonicotinoids, imidacloprid and thiacloprid were most toxic insecticides with 100% mortality at realistic field doses by ingestion method with sugar solution as a substitute of nectar after the exposure of 3hrs. Honeybee's workers exposed with insecticides mixed pollen grains showed that imidacloprid and clothianidin were most toxic as compared to other insecticides at recommended field dose with 100% mortality and minimum mortality with 60% was observed at thiacloprid field dose after 3hrs exposure. The results of contact toxicity showed that all four insecticides were most toxic with wet filter paper with 100% mortality at recommend field dose after the exposure of 3hr, and with dry filter paper imidacloprid and thiacloprid showed 100% mortality and acetamiprid and clothianidin with 53.3% mortality after the exposure of 3hrs at field dose. Overall conclusion from the present study indicates that from these four insecticides imidacloprid was the most toxic as compared to all others on both ingestion and contact method at recommended field dose.