Influences of an herbicide and an adjuvant on the behavior and colony growth of the common eastern bumble bee (Bombus impatiens)

Recent declines in bumble bee populations pose a risk to bee diversity and the pollination services provided to both agricultural and natural areas. Pesticides may be a factor in declines, but agrochemicals such as herbicides and adjuvants have rarely been tested for pollinator safety. Our goals were to determine if two commonly used agrochemicals, the adjuvant Dyne-Amic (Helena Chemical Co.) and the herbicide 2,4 D,  1) influenced colony growth, and /or 2) altered bumble bee foraging behavior in a field setting. Concentrations of the chemicals resulting in 10% bumble bee worker mortality (LC₁₀’s) were determined through oral exposures to be 3% for 2,4-D and 14% for Dyne-Amic. Entire hives were then treated with LC₁₀ doses of Dyne-Amic alone, 2,4 D alone, both chemicals, or none (control). Foraging trips and hive growth were measured using radio-frequency identification (rfid) technology. We found that both agrochemicals decrease the number of workers in a colony and colony weight. Additionally, 2,4-D treated bees took less foraging trips than control bees in one of two experiments. Our research highlights the some of the impacts of non-insecticidal agrochemicals on non-targets. Both herbicides and adjuvants are highly utilized worldwide, and further analysis of the full non-target impacts of these compounds is warranted.