Influence of pesticide use in fruit orchards during blooming on honeybee mortality in 4 experimental apiaries

Samples of dead honey bees (Apis mellifera L.) were collected periodically from 4 different locations during citrus and stone fruit trees blooming season to evaluate the potential impact of agrochemicals on honey bee death rate. For the determination of mortality, dead honey bee traps were placed in front of the experimental hives entrance located in areas of intensive agriculture in Valencian Community (Spain). A total of 34 bee samples, obtained along the monitoring period, were analyzed by means of QuEChERS extraction method and screened for 58 pesticides or their degradation products by LC-MS/MS. An average of four pesticides per honey bee sample was detected. Coumaphos, an organophosphate acaricide used against varroosis in the experimental hives, was detected in 94% of the samples. However, this acaricide was unlikely to be responsible for honey bee mortality because its constantly low concentration during all the monitoring period, even before and after acute mortality episodes. The organophosphates chlorpyrifos and dimethoate, as well as the neonicotinoid imidacloprid, were the most frequently detected agrochemicals. Almost 80% of the samples had chlorpyrifos, 68% dimethoate, and 32% imidacloprid. Maximum concentrations for these three compounds were 751, 403, 223 ng/g respectively. Influence of these pesticides on acute honey bee mortality was demonstrated by comparing coincidence between death rate and concentrations of chlorpyrifos, dimethoate and imidacloprid.