Recent studies have shown that cities provide refuge to native bees across a wide range of geographical locations and climates. Yet, we do not know the mechanisms that allow for increased bee diversity in cities. It has been proposed that social bees respond to urbanization in a more obvious fashion than solitary species. We selected the social sweat bee, Halictus ligatus, in order to elucidate possible mechanisms. Halictus ligatus is one of the most abundant bees across St. Louis city, and has been shown to respond to varying environmental conditions by altering its phenology. We hypothesize that Halictus will exhibit different phenology patterns, consistent with resource abundance and availability, across locations within the city of St. Louis, MO.
We collected individuals from May to October, 2013 to 2016. Specimens were brought back to the lab and curated. We assigned geographic areas within the city as treatments based upon floral resource availability (i.e., north, central and south city), as well as the management type (community garden, prairie pocket, urban farm) of the location. Because development of the tegula (ie, distance between wings) is directly proportional to resource availability, we measured the intertegular width and head width of females H.ligatus.
Results/Conclusions
The largest individuals, which correspond to foraging queens, were found in May, regardless of year. The next largest, unmated gynes, were observed in September, once more independent of year. The smallest bees were found during the summer months of June, July and August, consistent with workers collecting pollen for the brood. This trend was consistent for all the data collected in 2013-2016. In addition, there are apparent differences among north, central and south for both intertegular width and head width, indicating that there is likely a difference in resource availability or acquisition among the populations of Halictus ligatus across the city of St. Louis. How does this differentiation lead to better performance in a city environment remains to be investigated.