ARS | Publication request: Microsatellite analysis of bumble bee foraging in mass flowering agricultural fields

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 2, 2012
Publication Date: N/A

Interpretive Summary: Bumble bees are important native pollinators in North America. Each species of bumble bee has a species specific foraging range which determines how far individuals from one nest will fly to find food. This affects both the survival and success of the bumble bee nest, but also the pollen movement from plant to plant that the bumble bees visit. The current study investigates how far a common bumble bee, Vosnesenski's bumble bee, flies during clover bloom in the Willamette Valley of Oregon. We used DNA markers to determine the foraging distance and number of bumble bee colonies that were visiting ten clover fields in 2007 and 2008. In all, 768 bees were used in the analysis. Interestingly, Vosnesenski’s bumble bee seems to be capable of long distance flight and has one of the longest flight ranges (11.6km or 7.2 miles) of any bumble bee studied so far. This may have important implications on the movement of pollen across the landscape, including implications for isolation of fields where genetically modified crops are being grown. In addition to the long flight range, the number of colonies contributing pollination service to a single field can be quite large. On one intensively sampled field, we observed foragers originating from 152 different colonies. This implies that either the density of nests in the locality of the field is very high, or that bees are flying in from a long distance to forage for pollen and nectar.

Technical Abstract: Bumble bees, social insects that provide pollination services in native and agricultural habitats, have declined, in part, due to habitat fragmentation. They require food resources within foraging distances of the nest for colony survival and growth. Foraging distances of workers have been assumed to be short (<2.5 km), based primarily on estimates made in natural and semi-natural landscapes in Europe. Little is known about foraging distances of nearctic species, especially in fragmented patches of mass flowering crops in agricultural landscapes. Here, we studied the foraging patterns of Bombus vosnesenskii, a common species in the agricultural-dominated Willamette Valley in Oregon, USA. Workers from 10 clover fields collected during mid and late summer over two years were genotyped using eight microsatellite loci, and assigned to full sibling families (=colonies). After estimation of numbers of unseen species, we inferred the presence of 215 colonies from 472 bees genotyped in 2007, and 162 colonies from 296 genotyped in 2008 indicating that 46% and 55% of the bees, respectively, originated from different colonies. Across both years, 145 colonies were observed foraging in two fields, 22 in three fields, and two colonies on four fields, indicating that many colonies are utilizing common resources within the landscape. The foraging range for B. vosnesenskii workers was estimated to be at least 11.6 km, half the distance between fields visited by the same colonies that were furthest apart. The results indicate that bumble bee species with extended flight ranges can thrive in agricultural landscapes with fragmented mass flowering crops.