Habitat fragmentation and loss due to expanding agricultural land-use is one of the most prevalent threats to native wildlife, including pollinators. Programs such as the Conservation Reserve Program (CRP) are thus often aimed at creating or enhancing habitat within agricultural landscapes, which could benefit wild bees indirectly through improved bee performance. To determine the value of CRP plantings for cavity-nesting bees in northeastern Colorado, we surveyed 32 sites, including both managed rangelands and CRP plantings, with a combination of bamboo and wooden block trap-nests over the summer of 2014. We extracted all nests from trap-nests and collected data on both bee population size and individual female bee performance (measured as number of cells per nest). To estimate the success of the Conservation Reserve Program in promoting cavity-nesting bee populations and performance, we compared the mean number of nests found in rangeland and CRP sites as estimates of bee population sizes, and the number cells per nest as an estimate of female bee reproductive effort and performance.
Results/Conclusions
We collected a total of 283 nests from traps in the fall of 2014 and extracted 1,238 cells over the course of the winter and spring of 2015. All of the bees found in both site types were in the family Megachilidae, primarily in the genus Megachile. On average, CRP sites produced 23% more nests and 37% more cells per nest than rangelands. The higher number of nests per site could be attributed to higher population sizes in CRP fields or multiple generations of bees emerging during the 2014 summer season. The higher number of cells per nest indicates that females had higher reproductive success when nesting in CRP versus rangeland sites. These results suggest that CRP fields benefit cavity-nesting bees through increased populations and performance. This could likely be due to both a closer proximity to floral resources and greater abundance of floral resources on conservation land verses rangeland. Even though CRP fields have lower floral richness than rangelands, given that they are not grazed, it is likely that floral resources are more constant for foraging bees compared to rangeland sites. Overall, our results suggest that CRP plantings in agricultural areas of Colorado do provide crucial habitat for pollinators.