Abstract:  Bombus hypocrita (Hymenoptera: Apidae) is one of the dominant bumblebees in China, and is widely used as one of the most crucial pollinators in greenhouse due to easy mass-rearing, strong population and effective pollinating performance. However, it is often threatened by organophosphate and carbamate insecticides which are widely used in China, as these insecticides can inhibit the acetylcholinesterase (AChE) activity in insects. In order to avoid harm to bumblebees by these insecticides and improve the pollination technology and conservation of bumblebees, we optimized the reaction conditions to assay the AChE activity from the head of B. hypocrita, and evaluated the effect of six common organophosphate and carbamate insecticides on the AChE activity. The results showed that the optimal conditions are as follows: enzyme concentration 0.25 g protein/L, substrate concentration 0.8 mmol/L, pH 7.5, reaction temperature 40℃, and reaction time 5 min. The inhibition of six insecticides to AChE from B. hypocrita showed a dosage effect. The medium inhibition concentration (IC₅₀) values for chlorpyrifos, profenofos, triazophos, isoprocarb, bassa and propoxur are 0.39, 1.79, 0.42, 0.04, 0.43 and 0.63 mmol/L, respectively. The inhibitory effects of six insecticides to AChE from high to low are in the following order: isoprocarb> chlorpyrifos> triazophos> bassa> propoxur> profenofos, and B. hypocrita is more sensitive to isoprocarb than to the other five insecticides.

Key words:  Bombus hypocrita, acetylcholinesterase, orthogonal experiment, optimal assay conditions, insecticide sensitivity, medium inhibition concentration (IC₅₀)