Density and diversity of bees in the Midwestern agricultural landscape: Comparing vegetable and biofuel production to native remnant prairies

Background/Question/Methods

Recent trends in land management practices have led to dramatic population decline in bees and other insect pollinators.  Concerns about “Colony Collapse Disorder” in domestic honeybees, for example, have received widespread high-profile attention in the scientific community.  While concerns have centered mainly on the domestic honeybee, native bees also provide indispensable, cost-free pollination services to crops production.  Despite the value of native bee species, little is known about native bees in the Midwest region, and recent studies suggest their populations may be in decline due to a lack of native vegetation in this highly agricultural landscape.  Vegetable farms and lands managed for cellulosic biofuels have the potential to provide usable habitat, but their utility is not well understood.  We set up pan traps at organic vegetable farms and at a nearby biofuel production site and sampled over two summers to measure the pollinator species richness and composition.  Additionally, pollinator density and composition was compared to data from other studies of remnant prairie communities to determine whether pollinator communities differed between these land uses.

Results/Conclusions

During the first summer, 487 individual bees were collected.  The community composition at the biofuel site closely resembled the organic farm, with Halictidae bees in high abundance early in the season and Apidae bees dominating in the late season abundance scores.  Surrounding landscape variables were similar between sites, suggesting that diverse areas in an agricultural matrix, without a nearby remnant community with high bee diversity, maintain similar bee communities.

At the biofuel site, four treatments were seeded five years prior with varying species diversity.  There was a significant difference in flower abundance between seed treatments (p<0.05), suggesting bee abundance might vary accordingly.  However, bee abundance values for the different treatments were comparable, suggesting larger scale landscape factors influence community composition.

Remnant prairie populations are superficially more diverse and further tests must be performed in order to determine whether landscape variables, plant community composition, lack of source populations, or a combination of all contribute to the diversity and abundance of isolated bee communities.  Additionally, a pollen load study will be beneficial in determining the efficacy of native bees as a suitable alternative to managed European honeybees.