The roles of floral resource proximity to nesting substrate in wild bee nest-site selection

Background/Question/Methods Native bees are seen as an efficient alternative for pollination services in crop agriculture.   Farmers currently rely on Apis mellifera for pollination, but colonies of this species are in a decline due to disease and pests.  There is a need to understand the habitat dynamics of native bees and proper management practices that will ensure their survival.   In this study I tried to demonstrate how ground bee nest site selection is influenced by floral availability. The key question in this study is: Does host plant diversity and abundance in three abandoned field localities (Grassland, Bull Pasture, Shrubland) influence the decision of ground bees to nest on those sites? The study was conducted at Blandy Experimental Farm in Northern Virginia, Summer 2008. Twenty plots were established across three different localities to measure bee nesting preference for their flower species composition and abundance. Localities differed slightly in species composition and vegetation structure. All flowers within a 50m radius from the plot were counted the same day that each plot was surveyed for bee nest abundance to correlate flower availability with nesting. Bee species were collected with a bug net at various locations away from plots to decipher plant species use by specific bee species on the same plant species that were found in the vicinity of the plots. Bees were collected away from the plots for it not to affect our results, since we would be intervening with the species that could potentially be nesting in the plots.

Results/Conclusions

Despite different species compositions between localities, we found localities to have similar levels of species diversity (p=.2924). Overall, floral species diversity was not correlated with the abundance of nesting bees per plot (Spearman; p=0.1995). Nevertheless, when broken down by field type, we found that the shrubland locality was positively correlated with abundance of nesting bees (p= .017) and could possibly reflect the characteristic vegetation structure of a shrub habitat. Although we could not sustain the idea that floral diversity was an important factor for nesting site selection per plot, the numbers of nesting bees per plot were positively correlated with the floral abundance of attractive flower species. These results support the theory that the proximity of nesting resources to abundant floral resources is important for ground-nesting bees even at small scales (plot) while the importance of floral diversity can only be seen at larger scales (locality).