Low-dose pesticide effects in Apis mellifera: testing hormesis and reviewing changing trends in honey bee toxicology research

Abstract

Honey bees (Apis mellifera) dominate crop pollination worldwide and are often considered the most important pollinator of agricultural crops. As pollinators, honey bees are likely to encounter insecticides in the field. Neonicotinoids are widely used insecticides that have been at the center of the pollinator-pesticide debate. Hormesis is a biphasic dose response whereby exposure to low doses of a stressor can stimulate biological processes. Insecticide-induced hormesis has been recorded in insects and bees. My thesis examined the idea of hormesis within honey bees. Specifically, I examined whether low doses of a neonicotinoid would stimulate honey bee longevity. Groups of honey bees were individually treated with doses of imidacloprid and kept in bee cages. Their survival was recorded every day until the end of the experiments to determine longevity. In this thesis, I also examined the shifting focus of honey bee toxicology over the decades in an attempt to observe how research has changed, and determine how prevalent insecticide-induced hormesis is within the honey bee literature. I conducted a search using Web of Science to broadly examine pesticide toxicology research on pollinators and then specifically Apis species from 1950-2019. Another, more comprehensive search was done where I examined a total of 73 papers from three specific journals, published between 2000 and 2019, all of which examined honey bees and neonicotinoids. Exposure to low doses of imidacloprid did not result in stimulation of honey bee longevity. I found that most toxicology research surrounding pollinators and Apis species, alike, was published after 2010. I found there to be a focus on harmful sublethal effects and less of a focus on stimulatory effects or hormesis. In studies examining honey bees and neonicotinoids, I found the number of studies that used probable exposure scenarios was consistent throughout the years. Studies that found neonicotinoids to have no and negative effects on honey bees was another consistent pattern over the time span I examined. The possibility of hormetic responses in honey bees has been overlooked in the literature. By studying hormesis new information into how bees adapt to exposure to neonicotinoids could be revealed. This could provide impactful insights for those involved in the pesticide-pollinator debate.