D3120: Toxicity of spray adjuvants combined with pesticides to adult honey bee workers

Spray adjuvants are composed of “inert” principal functioning agents and do not undergo the same testing for bee safety as traditional pesticide active ingredients. These products are widely used in California almonds during bloom and pollinating honey bee colonies can be exposed to these applications. Primary research on the effects of adjuvants on honey bees is scarce and has focused on the organosilicone surfactant class of pesticide adjuvants. This study aimed to identify the acute effects on adult worker honey bees of a broad range of adjuvants when applied alone and in combination with common fungicides and insecticides applied during almond bloom. We aimed to simulate direct spray exposure through application with a Potter Spray Tower to treat 3-day-old workers with adjuvants, fungicides and insecticides at field relevant application rates. This research showed that the adjuvants Dyne-Amic, Surf-90, and Liberate can cause acute effects when applied alone. However, adjuvants are meant to be applied in tank mix combinations. This research showed that common tank mix combinations with pesticides demonstrated significantly increased toxicity over that of their constituents. These findings highlight a potential explanation for the honey bee losses reported during almond bloom and highlight the need for additional research to identify adjuvants and adjuvant-pesticide combinations carrying risks to insect pollinators.