Bee populations are declining. In 2014, of the 407 European bee species with known population trend data, 37% of those species were in decline. There are numerous explanations behind this decline, from increased parasitism, habitat loss, pesticide use, and climate change. Bumblebees (Bombus spp.), which provide a myriad of ecosystem services, have been among the groups showing significant declines. The historic range of the Rusty Patched Bumble Bee (Bombus affinis) has contracted by 87%, and in 2017, was listed on the U.S. Federal Endangered Species List. Numerous other Bombus are also declining in the US. In Virginia, declining bumblebees include Bombus pensylvanicus, Bombus fervidus and Bombus auricomus. From Mid-June to the end of July in 2019, common bumblebees, B. impatiens, and B. griseocollis, along with declining B. pensylvanicus, B. fervidus and B. auricomus were collected from sites primarily in Fauquier County, Virginia to understand whether there is a difference between declining and common Bombus spp. in the plants they used for pollen foraging. We collected pollen loads from the corbiculae and stained the pollen using carbol fuchsin. Pollen grains were identified at the genus or species, creating an overall pollen composition profile for each Bombus spp. collected.
Results/Conclusions
For analysis, we included the five most dominant pollen species categories: Solanum carolineaus (55.6%), Carduus spp. (5.7%), Trifolium spp. (15%), “Other” (12.5%), and “Unknown” (11.0%). “Other” was a group that consisted of species that were identified but not present in high numbers. “Unknown” was a group that consisted of 25 unknown species that were present, however, most of the unknown species made up less than 1% of the total pollen collected. A principal component analysis revealed that B. auricomus and B. fervidus utilized “Other” significantly more often and underutilized Trifolium relative to other the Bombus. Common bees, B. impatiens and B. griseocollis collected a more limited diet of S. carolineaus, Carduus spp. and Trifolium spp., with the declining B. auricomus and B. fervidus collected pollen from a broader group of seemingly less abundant plants (Other and Unknown). Comparative analysis of the pollen compositions of declining species and the more common Bombus spp. can help inform what plant species are valuable to threatened Bombus spp. Analysis of pollen is a powerful tool in understanding how habitat loss and changing floral diversity and distribution may be impacting B. pensylvanicus, B. fervidus and B. auricomus.