Risk posed to honeybees (Apis mellifera L. Hymenoptera) by an imidaclopridseed dressing of sunflowers

In a greenhouse metabolism study, sunflowers were seed-treated with radiola belled imidacloprid in a 700g kg(-1) WS formulation (Gauchoo(R) WS 70) at 0 .7mg Al per seed, and the nature of the resulting residues in nectar and po llen was determined. Only the parent compound and no metabolites were detec ted in nectar and pollen of these seed-treated sunflower plants (limit of d etection <0.001mg kg(-1)). In standard LD50 laboratory tests, imidacloprid showed high oral toxicity to honeybees (Apis mellifera), with LD50 values b etween 3.7 and 40.9 ng per bee, corresponding to a lethal food concentratio n between 0.14 and 1.57mg kg(-1). The residue level of imidacloprid in nect ar and pollen of seed-treated sunflower plants in the field was negligible. Under field-growing conditions no residues were detected (limit of detecti on: 0.0015 mg kg(-1)) in either nectar or pollen. There were also no detect able residues in nectar and pollen of sunflowers planted as a succeeding cr op in soils which previously had been cropped with imidacloprid seed-treate d plants. Chronic feeding experiments with sunflower honey fortified with 0.002, 0.00 5, 0.010 and 0.020mg kg(-1) imidacloprid were conducted to assess potential long-term adverse effects on honeybee colonies. Testing end-points in this 39-day feeding study were mortality, feeding activity, wax/comb production , breeding performance and colony vitality. Even at the highest test concen tration, imidacloprid showed no adverse effects on the development of the e xposed bee colonies. This no-adverse-effect concentration of 0.020mg kg(-1) compares with a field residue level of less than 0.0015mg kg(-1) (= limit of detection in the field residue studies) which clearly shows that a sunfl ower seed dressing with imidacloprid poses no risk to honeybees. This concl usion is confirmed by observations made in more than 10 field studies and s everal tunnel tests. (C) 2001 Society of Chemical Industry.