Impact of winter severity and duration on wild bee abundance in Plymouth County, Massachusetts

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Alexander D. VanHelene, Adam Germaine, Folusho Ajayi, Christina Orazine, Prisca Sanon, Andrew Oguma and Michael Bankson, Division of Science and Mathematics, Massasoit Community College, Brockton, MA, Kehinde Agbeleye, Massasoit Community College, Brockton, MA

Background/Question/Methods
Bees are keystone organisms, essential for ecosystem health, and their potential decline has elicited concern for their long-term survival. Anthropogenic changes are thought to negatively impact wild bee communities by limiting nesting and foraging resources. In addition to these long-term changes in the physical environment, transient or seasonal changes may also be important in understanding long-term changes in the bee community. For example, some studies have shown that changing weather patterns may create phenological mismatches between bees and plants. Therefore, we investigated if variations in temperature and seasonal timing correlate with bee abundance. We hypothesized that categorically warmer years, mean temperature of the coldest month, the timing of frosts, and the extent of temperatures over 10°C (growing degree units) of the previous summer will influence bee abundance. We compared these variables to bee abundance sampled from 2016-2019 using pan traps and sweep nets at six sites of varying land attributes in Plymouth County, Massachusetts.
Results/Conclusions
Total bee abundance, spring bee abundance, and fall bee abundance did not differ significantly between warm and cold years (p=0.24, p=0.94, and p=0.26, respectively). Conversely, Agapostamon had two-fold higher spring abundance during cold years (p<0.05) but not total (p=0.21) or Fall (p=0.27) abundance. Years with early versus late last spring frosts showed no significant differences in total abundance (p=0.68). However, years with early last spring frosts had lower abundance in spring (p=0.01), but not Fall (p=0.71) suggesting a rebound late in the season. Growing degree units during the previous summer predicted spring abundance (p<0.001), but not yearly abundance (p=0.68). Together, these data suggest that the timing of last spring frost and growing degree units of the previous summer predict early-season bee abundance. The positive effect of cold weather on Agapostemon abundance suggests winter temperature may have genera-specific effects. Higher spring abundance following summers with a greater extent of temperatures amenable to plant growth suggests that higher floral resources before the cold season increases spring abundance. In conclusion, changing climate necessitates an understanding of weather-based predictors of pollinator abundance.