Exposure of honey bees during pesticide application under field conditions

Although pesticides are assessed before registration for whether or not they are harmful to bees there is little information available about the exposure of individual bees during pesticide application under practical conditions. We investigated the exposure of bees in real application situations in flowering apple orchards and Phacelia fields (Phacelia tanacetifolia Benth) in the years 1992-1997. In application trials we used a fluorescent tracer (sodium-fluorescein) at a dose rate of 20 g per 10 000 m(2) sprayed area. Bees were collected at the closed hive entrance over a period of 20-30 min in 5-min intervals. The deposit was individually measured on about 100 individual bees per sampling point. Mean initial deposit per trial varied from 1.62 to 20.84 ng/bee in apple orchards (nine trials) and from 6.34 to 35.77 ng/bee in Phacelia crops (five trials) with very few highly contaminated individuals. Earlier investigations prove these magnitudes to be realistic. The data give information concerning maximum exposure of individual bees. Results contribute to the discussion of altering concentration-based dose recommendations to product quantities related to the sprayed area.