Lethal and sublethal effects of some insecticides recommended for wild blueberry on the pollinator Bombus impatiens

Managed and wild colonies of common eastern bumble bee (Bombus impatiens Cresson) (Hymenoptera: Apidae) are effective pollinators of wild blueberry (Vaccinium angustifolium Aiton) (Ericaceae) in Atlantic Canada. Because insecticides are used during bloom to manage insect pests, bumble bees may be at risk of exposure. We therefore assessed the susceptibility of B. impatiens to some insecticides used or projected for use in blueberry pest management. Workers were killed by topical applications of spinosad, spinetoram, deltamethrin, and phosmet, but not flubendiamide. Similarly, when ingested in honey solution, spinetoram and deltamethrin were toxic, whereas flubendiamide did not cause mortality up to double its recommended label rate. In another experiment, workers were fed one sublethal dose of contaminated honey solution and placed in microcolonies to assess impacts on feeding, life span, and reproduction. The highest concentration of deltamethrin (17 mg a.i./L) reduced feeding. Workers treated with deltamethrin had shortened life spans and produced fewer males. Flubendiamide (2000 mg a.i./L) and spinetoram (0.8 mg a.i./L) caused no sublethal effects. These results indicate that flubendiamide should be safe to apply to blueberries where B. impatiens is foraging, while some other insecticides we tested may be hazardous under different exposure scenarios.