Rachel Shuler, 2003

Oberlin College

Farming for bees: pollination as ecosystem service

Native beesí contribution to crop pollination provides an invaluable ecosystem service. In spite of the value of a healthy population of native bees, the influence of agricultural practices on their survival is not well understood. In this study we investigate the relationship between farming practices and the diversity and abundance of native pollinators. We determined the agricultural practices and conducted bee surveys on farms growing cucurbits in Virginia, Maryland, and West Virginia. Although many farmers manage or rent non-native honey bees for cucurbit pollination, cucurbits host many native bees, including bumble bees, sweat bees, and the cucurbit specialist squash bee (Peponapis pruinosa). By far the most surprising finding in this study was the sheer abundance of Peponapis, which has been shown to be a very dependable and effective cucurbit pollinator where it occurs. Although they didnít emerge until mid-July, we found squash bees foraging on almost every farm. This wide-spread dispersal could be a result of excellent survival rates at each farm or recolonization from source populations. Although it was ubiquitous, Peponapis population density differed substantially among farms. Farms with no-till practice had the highest Peponapis density, potentially indicating a higher nest survival rate for this ground-nesting bee at sites where the field is undisturbed. Density of the social generalists Bombus spp. was higher on more diverse farms while that of Peponapis was unaffected by diversity. This finding supports the fact that bumble bees need flowers in blossom throughout the season to support a growing hive whereas squash bees are solitary, oligolectic, and produce only one generation per year. Apis densities were unaffected by keeping hives, demonstrating honey beesí low affinity for Cucurbita while suggesting the possibility of feral hives. Abundance and diversity of native species did not increase on organic farms, though this is potentially because most of the conventional farms in our data set were careful not to spray pesticides during floral antithesis. In the future it would be interesting to integrate these data with GIS information about the proximity of natural habitat to each farm.

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