A semi-field study to evaluate effects of sulfoxaflor on honey bee (Apis mellifera)

A semi-field study was conducted to investigate the effect of sulfoxaflor on honey bees and the residues in matrices after being used on cucumber. A suspension of 22% sulfoxaflor concentration was applied on cucumber at full bloom, at the rates of 75 g a.i./ha and 100 g a.i./ha, both with 2 applications at 6-day interval. Colonies were introduced into the tunnels one day after the first application, then mortality and behaviour of the test bees were observed and recorded every day. Cucumber flowers were taken and analysed for sulfoxaflor residues. The second application occurred 6 days later, then, observations of mortality and behaviour were conducted for 5 days, and then the colonies were removed from the tunnels and transported back to the apiary for 14 days additional observation. Besides, general conditions of the colonies were assessed before and after exposure, at the end of the field study. After being introduced into the tunnels, the colonies stabilized after 3 days’ adaption. During the exposure period, sulfoxaflor showed lethal toxicity on bees, but the effect was less than that caused by dimethoate. After being removed from the tunnels, the mortalities of all groups fluctuated at a low level, indicating that sulfoxaflor had no long-term lethal effect on bees. During the whole exposure period, sulfoxaflor had no effect on the flight intensity of the bees. Meanwhile, sulfoxaflor had no obvious adverse effect on the strength and the condition of the test colonies. Residue analysis showed that: on the days of application, the residue of sulfoxaflor in cucumber flower was between 5.004 mg/kg and 5.832 mg/kg. After the applications, the residue of sulfoxaflor reduced gradually, until the 6th day after the first application, the residue reduced to 0.100~0.198 mg/kg, until the 5th day after the second application, the residue reduced to 0.155~0.304 mg/kg.