Compatibility of traditional and novel acaricides with bumblebees (Bombus terrestris): a first laboratory assessment of toxicity and sublethal effects

Abstract

This project assessed the potential hazards of different classical and novel acaricides against an important non-target and beneficial insect for the pollination of wild flowers and cultivated crops, the bumblebee Bombus terrestris (L). Twenty-three acaricides used commercially in the control of phytophagous mites (Acari) were tested in greenhouses and/or the open field. Side effects included acute mortality and also sublethal effects on nest reproduction. The different compounds were administered in the laboratory via three different worst-case field scenario routes of exposure: dermal contact and orally via the drinking of treated sugar water and via treated pollen. The compounds were tested at their respective maximum field recommended concentration (MFRC), and, when strong lethal effects were observed, a dose-response assay with a dilution series of the MFRC was undertaken to calculate LC(50) values. From the different acaricide classes, several chemistries caused high levels of acute toxicity in bumblebee workers, especially bifenthrin and abamectin which resulted in 100% mortality by contact. In addition, several acaricides tested were found to have a detrimental effect on drone production. For oral exposures via treated sugar water, the dose-response assay showed the LC(50) values for abamectin, bifenazate, bifenthrin and etoxazole to be 1/15 MFRC (1.17 mg AI L(-1)), 1/10 MFRC (9.6 mg AI L(-1)), 1/83 MFRC (0.36 mg AI L(-1)) and 1/13 MFRC (4.4 mg AI L(-1)) respectively, indicating that their use should be carefully evaluated. Overall, the results suggest that most of the acaricides tested are compatible with bumblebees, with the exceptions of abamectin, bifenazate, bifenthrin and etoxazole. However, the risks also depended on the type of treatment. As a result, the sugar water treatment seems to present the worst-case situation of exposure, indicating that this approach is suitable for determining the hazards of pesticides against bumblebees. Finally, it is suggested that future tier testing under more field-related conditions is required for a final decision of their risks.