The effects of thiamethoxam on Bombus impatiens foraging efficiency

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Emma C. Grover, Environmental Sciences, University of Virginia, Charlottesville, VA and T'ai Roulston, Environmental Sciences, University of Virgnia, Boyce, VA

Background/Question/Methods
The recent and continual decline in the global bumble bee population has been a major source of anxiety for environmentalists, and pesticides are potentially one of the main factors driving this unwanted development. This experiment broadly examines whether a particular neonicotinoid pesticide, thiamethoxam, impacts the foraging efficiency of an adult worker bumble bee (Bombus impatiens). Sublethal levels of thiamethoxam were established through experimentation in the lab. We determined that exposure to dosages of 25 μg L-1 of thiamethoxam and below were nonlethal and showed no evidence of effect on Bombus impatiens individuals in the lab. We then intentionally chose to test the bees with a level of pesticide that was not only sublethal but showed no apparent effects in the lab. Therefore, we could see how this toxic substance interferes with the challenging task of foraging naturally in the environment. Individual bumble bees were then randomly assigned to either a pesticide or control treatment, exposed to their treatment, and returned to a naturally foraging colony system. Over the course of five weeks, the movements of all the bees in and out of the colony were tracked with RFID technology. Their weights were documented before and after each foraging trip.
Results/Conclusions
We found that bees exposed to thiamethoxam were significantly less efficient at foraging than bees that did not come consume the poison. Bumble bees in the control treatment were able to return from foraging trips carrying a larger proportion of their body weight than those in the pesticide treatment. In addition, control bees were able to bring back a greater amount of resources with respect to the duration of time they spent outside the colony. Therefore, it is clear that the pesticide produces negative, sublethal effects within the bees, decreasing their ability to assist their colony in nutrient collection. This experiment seeks to provide information that can better identify the significance of pesticides in the decline of bumble bees while also shedding light on conceivably influential and contemporary areas of methodology.