Effects of altitudinal gradients on social thermoregulation and pesticide sensitivity in bumble bees: Insights from a low-cost and automated behavioral tracking method

Bumble bee populations span large ranges, inhabit radically different environments across North America, and face diverse environmental pressures. Research shows that precipitation and temperature are key variables in determining environmental niches of bumble bee species, and there is evidence of local altitudinal and geographic adaptation and differentiation in populations’ thermal tolerances, both within and between species. There is also a growing body of research quantifying the effects of sub-lethal neonicotinoid exposure on behavior and thermal physiology of wild bees. Given the widespread use of this neurotoxic insecticide in the United States and globally, it is vital to understand whether neonicotinoid exposure differentially affects distinct bumble bee populations based on habitat-specific adaptations. Here, we examine the effects of cold and neonicotinoid stress on the within-nest social behavior of 45 Bombus vosnesenskii colonies reared from queens caught in Hood River, Oregon. We test whether intra-colony variation in critical thermal limits is correlated to behavior across a range of temperatures, and whether neonicotinoid exposure might alter these results. To test this, we developed a low-cost, high-throughput tracking system takes advantage of recent advances in tracking algorithms that can be implemented on open-source devices. We use this to automatically monitor the behavior of uniquely-identified workers across colonies. This cheap and reliable method of data capture could be broadly applicable for studying bumble bee behavior, which is especially useful for documenting the behavioral effects of neurotoxic insecticides such as neonicotinoids.