Enhancement of pollination by native bees in blueberries and cranberries
Pollination is critical for production of blueberries and cranberries. In the Pacific Northwest, growers rent honey bee hives for pollination. However, honey bees do not perform as well as native bees in these crops due to prevailing weather conditions during bloom, and due to their preference for other flowers from which nectar is easier to access. In contrast, native bees forage in wind, rain and on cloudy days. Also, native bees are less expensive and invasive. Hence, the study was conducted to determine strategies for enhancing populations of native bees for increasing pollination and improving yield and grower profit.
1. Estimate native bee pollinator species diversity and abundance in berry fields.
2. Compare honey bee and bumble bee foraging behaviors in berry fields.
3. Evaluate the impacts of insecticide sprays on native bees.
4. Examine strategies for enhancing native bees in berry fields.
5. Build capacity in growers to identify, protect and enhance native bee pollinators in their fields for increasing berry production.
Objective 1: Estimate native bee pollinator species diversity and abundance in berry fields.
Methods: Native bee abundance was monitored in three blueberry fields in the Willamette Valley in western Oregon in 2009 and 2010. Native bees were sampled using blue vane traps that were set up, three per site, for 48 hours. Bees were sampled over six weeks before, during and after bloom. Bees that were trapped were preserved and identified.
Results: In all, over the two years, 51 species of native bees belonging to 16 genera and five families were trapped (Table 1). Overall, there were greater numbers of bumble bees than honey bees trapped. Seven bumble bee species were trapped, of which Bombus vosnesenski was captured in greatest abundance. In 2010, the region experienced very cool temperatures. As a result there were three times fewer bees caught compared with the previous year.
Representative specimens of each taxa collected are being processed for development of a reference collection of native bees present in the Willamette Valley during bloom in blueberries.
Methods: Blue vane traps were placed around cranberry bogs of four growers. At each site, two traps were set for 24 hours. Sampling was conducted sixteen times over the two year study. Bee specimens that were trapped were preserved and identified.
Results: In all, over the two years, 27 species of native bees belonging to 12 genera and five families were trapped (Table 2). Bumble bees (Bombus spp.), metallic sweat bees (Agapostemon spp.) and small sweat bees (Lasioglossum spp.) were recorded in higher abundance than honeybees. Bumble bees comprised 25.1% of all bees captured, with five species represented: B. vosnesenskii B. mixtus, B. melanopygus and B. californicus. The most abundant was B. vosnesenskii, which constituted 50.1% of all trapped bumble bees. Two species of Agapostemon were trapped, of which A. texanus (24.6% of all bees and 98.5% of all Agapostemon captured) was more abundant than A. virescens. Bees in the Lasioglossum species complex, which could not be separated to named species, were also trapped.
A reference collection of native bees associated with cranberries was prepared and donated to the Coos County Extension office.
Objective 2: Compare honey bee and bumble bee foraging behaviors in berry fields.
Pollen traps were placed for two days in honey bee hives in three blueberry orchards in 2009 and 2010, one-three times during bloom. A subsample of 50 pollen loads from each trap was subjected to acetolysis which burns internal parts so that structures on the external pollen shell are preserved for identification. Out of 850 loads processed over two years, on average, 0.38% of the pollen loads in 2010 alone consisted of blueberry pollen (Fig. 1). In a separate study, out of 65 honey bees collected on flowers, only 3% had pollen loads. In comparison, 23% of bumble bees collected at the same time had pollen. Thus, honey bees do not appear to forage extensively for pollen in blueberries. This may be because blueberries need buzz pollination – the flowers have to be shaken by bees for pollen release. Unlike bumble bees, honey bees are unable to buzz pollinate. Thus, alternative pollinators are required for blueberry pollination.
On four different dates in May, June and July 2009, we collected honey bee pollen using pollen traps on four honey bee hives on an Oregon cranberry farm. Later, in the laboratory, we used acetolysis to process the samples and are currently in the process of using light microscopy to identify the pollen grains. The results thus far are presented in Table 3.
Objective 4. Examine strategies for enhancing native bees in berry fields.
Bloom in berry crops lasts around three weeks while native bee life cycles last several months. Hence native bees need alternative foraging resources before and after crop bloom. To determine the presence of floral resources in the landscape, the landscape surrounding berry fields was scored, and the plants that are present in hedgerows and in adjacent habitats were recorded. Organization of data for determining if there are any correlations between native bee abundance and floral resources in surrounding habitats is in progress.
Meanwhile we are compiling a list of plants that bloom before and after bloom in berry crops. This will be presented to growers interested in adding floral resources to their orchards for build-up of native bees.
Objective 5. Build capacity in growers to identify, protect and enhance native bee pollinators in their fields for increasing berry production.
Native bees that are common in blueberry and cranberry fields during bloom were photographed and a pictorial identification key was prepared. A bee identification workshop was organized for cranberry growers on February 3, 2010 in Bandon, Oregon. Fifteen cranberry growers signed up for the workshop. They were initially provided background about external characters in bees. Subsequently they learned to distinguish between honey bees, bumble bees and yellow jackets by examination of specimens under a microscope. Then, using the pictorial key, they learned the differences between various bumble bee species. They also learned to recognize other native bees such as sweat bees, Agapostemon and blue orchard bees, Osmia, to the genus level.
A similar bee identification workshop is being organized for blueberry growers in winter 2011.
Impacts and Contributions/Outcomes
At the Annual Cranberry Growers’ meetings in February 2010, we gave talks during which research plans for the year were presented to all 100 attendees. Subsequently, we met with growers to discuss future research and extension plans.
The research has increased awareness about the value of bumble bees in pollination of berry crops. Bumble bees are not commercially available in Oregon since all the commercial species are not native to the state; hence, growers have to rely on native populations which are not consistent from year to year. As a result, beekeepers have exhibited interest in rearing native bumble bee species. One honey bee keeper was motivated to submit a Small Business Innovation Research grant to USDA for rearing of native bumble bee species. Two other bee keepers have sought advice on how to rear bumble bees. In response we are developing a protocol fr dissemination to bee keepers.
The study has generated interest from blueberry and cranberry growers in enhancement of floral resources in areas surrounding their berry fields/bogs. This led to preparation of a list of plants that bloom during periods before and after bloom.
The feedback from the cranberry workshop was positive. One grower participant indicated in an email after the workshop: “The workshop was very interesting for Esther and I. On Monday I saw a very large Bombus melanopygus and a smaller Bombus vosnesenskii in my yard on some heather. I was very proud of the fact that I actually knew what they were specifically, instead of saying a kind of black bumble bee and a kind of orange one. Also interesting to know about their life cycles and realize that these were both queens.”
Presentations made related to blueberry and cranberry pollination research:
Skyrm, S., Rao, S. and Fisher, G. Impact of pesticide residues on a native bumble bee pollinator, Bombus vosnesenskii (Hymenoptera: Apidae). Annual Pacific Northwest Insect Management Conference 69th Annual Meeting, Portland, OR. January 2010.
Rao, S., McKenney, M. and Phillips, K. Native Bees and Honey Bees Associated with Cranberry Pollination, 2010 Oregon Cranberry School, Bandon, OR. February 2010.
Phillips, K., Rao, S., Stephen, W. P. and White, L. Bumble bees versus honey bees: a comparison of pollination success in Oregon cranberries. Annual Meeting of the Pacific Branch Entomological Society of America, Boise, ID, March 2010.
Phillips, K., Rao, S., Stephen, W. P. and White, L. Comparison of pollination efficiency by bumble bees and honey bees in Oregon cranberries. Insect Explorer Series, Entomology Program, Oregon State University, April 2010.
McKenney, M. Rao, and Stephen , S. Pollination by Native Bees and Honey Bees in Cranberry. Celebrating Undergraduate Excellence, Oregon State University, May 2010.
Phillips, K. Oregon cranberry pollination research updates. Cranberry Field Day, Oregon State University Extension Service and Oregon Cranberry Growers Association, June 2010.
Phillips, K., Rao, S., Stephen, W. P. and White, L. Bumble bees versus honey bees: a comparison of pollination success in Oregon cranberries. Annual Meeting, Entomological Society of America, San Diego, CA, December 2010.
Publications related to blueberry and cranberry pollination research:
Phillips, K., White, L., Rao, S., and Stephen, W. P. 2010. Bumble bees versus honey bees: a comparison of pollination success in Oregon cranberries. South Coast Grower News. 4(2): 4-5.
Skyrm, K. and Rao, S. 2010. Impact of pesticide residues on a native bumble bee pollinator, Bombus vosnesenskii (Hymenoptera: Apidae). In Proceedings of the 69th Annual Pacific Northwest Insect Management Conference. Portland, OR. pg. 15-18.
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