The majority of native and naturalized bees in the U.S. are solitary ground-nesting bees.  The natural habitat that these wild bees require for foraging and nesting is steadily decreasing with the increase in urbanization and commercial agriculture.  The study of nesting substrate and materials is lacking in the literature.  It is thought that ground-nesting bees assess soil conditions before initiating a nest.  Prior observational studies found nest presence to correlate with certain soil characteristics.  Due to the descriptive quality of those studies it is still unclear whether bees prefer these characteristics or respond to other correlated factors.  It is also unclear if areas can be prepared in a way that generally promotes ground-nesting bees.  This is the first study to manipulate substrate characteristics to examine preferences of ground-nesting bees.  In this study I tested the influence of moisture and ground cover on attracting ground-nesting bees to nest at Blandy Experimental Farm in Northern Virginia.  The design consisted of 20 plots distributed across three different habitats in an agricultural landscape.  All plots were assigned a moisture treatment (ambient rainfall (dry) vs. additional simulated rainfall (wet)) and a vegetation type (existing, revegetation with a cover crop, or bare ground). Bee surveys in each plot were done twice a month from June to September, 2008 to quantify nest initiation.  In addition soil moisture and floral resource availability were measured during survey rounds. 

Results/Conclusions

Overall, the ground-nesting bee community at Blandy Experimental Farm preferred to nest in bare ground and revegetated ground over existing vegetation, confirming the conclusions of observational studies but also demonstrating that the substrate can be manipulated to influence local choices.  Bee response to moisture was more complicated, differing with vegetation treatment.  Revegetated ground alone was not the attraction for the bees.  Specifically, female bees preferred nesting in revegetated plots that received the simulated rainfall over revegetated plots that were subject only to ambient rainfall.  This response may simply be explained by inherent species/genera specific preferences which are currently being analyzed; however the mechanism for this is not well understood and will be further investigated this spring in a controlled experiment.  Survival of these pollinators depends on an increased understanding of their life histories.  Identifying these controlling variables could encourage land owners and managers to incorporate management techniques that increase potential nest sites thereby increasing bee species abundance and diversity and insuring pollination services.