Acute toxic effects of insecticide-fungicide-adjuvant combination on honey bees

Emily Walker
Graduate (MS)
Reed Johnson

Significant decreases in honey bee (Apis mellifera) populations have been reported by beekeepers and farmers over the last couple of decades without a clear explanation. This decrease in the honey bee population poses a major problem for the California almond industry because of its dependence on honey bees as pollinators. Pesticides are a common factor that affects honey bee health and thought to be a possible explanation for these losses. Pesticide adjuvants are relatively unexplored and lightly regulated yet widely used in agriculture. This research aimed to determine if tank mix combinations of pesticides and pesticide adjuvants applied during almond bloom were a possible explanation for these honey bee losses. In this study, we mimicked the spray application route of exposure by using a Potter Spray Tower to spray adult honey bees with the various treatments. Acute mortality was recorded for each treatment and data was then compiled and analyzed in R. This research determined that the combination of the fungicide Tilt (active ingredient propiconazole) and the insecticide Altacor (active ingredient chlorantraniliprole) displayed synergistic toxicity that was not observed when the treatments were applied individually. This study also showed that the adjuvant Dyne-Amic was toxic to honey bees at concentrations slightly above the recommended field applications (LC50 3.05X). Dyne-Amic also showed synergistic toxicity when combined with the fungicide Pristine (active ingredients pyraclostrobin and boscalid) and the addition of Dyne-Amic increased toxicity in the Tilt and Altacor combination treatment. These results suggest that the application of Tilt and Altacor in combination with an adjuvant at the recommended field application rates could cause significant mortality in adult honey bees. These findings highlight a potential explanation for honey bee losses around almond bloom and present novel findings that adjuvants can be acutely toxic to honey bees. The findings from this study support that adjuvants should receive the same testing as other pesticides.