The bumble bee pollination findings offer promise for the use of bumble bee crop pollinators as an alternative to European honey bees, whose populations have recently declined in many areas of the United States.
Red clover, which is grown for forage and as a rotation crop to improve soil, is raised for seed in western Oregon's Willamette Valley. It will not produce seed without pollination, so growers typically place two to five European honey bee hives on each hectare.
Search for Alternative Pollinators
Bee diseases, mites, and colony
collapse disorder have recently limited availability and resulted in
higher costs for hive rentals. Given these changes, an alternative
pollinator for red clover seed crops is needed.
Worldwide there are
over 200 species of bumble bees; some of whom are known to pollinate
red clover. While commercially reared bumble bee species are available
to growers elsewhere, they are considered exotic species in Oregon and
cannot be introduced into the state. This leaves Oregon growers
dependent on naturally occurring populations of bumble bees as
pollinators. However, there is currently no information on the
pollination efficiency of native bumble bee species.
Scientific Evaluation of Blooms and Seed Set
Through funding from the Clover Commission, scientists at Oregon State University investigated native bumble bees in commercial fields of red clover seed crops in the Polk County region of the Willamette Valley. Prior to bloom, researchers covered plants with mesh-screened cages. European honey bee hives were placed in some cages and nests of B. vosnesenskii, a native Oregon bumble bee,in others. Some cages were also left vacant. After bloom, seed yield and seed set were compared amongst the different cages. Seed set was also evaluated in four different fields without cages to assess the efficiency of existing bee pollinators. In addition to analyzing seed set, researchers assessed the diversity and abundance of native bumble bees through visual observations of foragers on red clover flowers and through trapping bumble bees in blue vane traps.
Pollination Differences between Bumble Bees and Honey Bees
While there were no
differences in seed yield or average seed set in cages with bumble bees
compared to honey bees, the study revealed:
- Variability across
cages was lower with bumble bees indicating that bumble bee pollination
is more uniform than pollination by European honey bees.
- The abundance of bumble bee peaked during
mid-to-late bloom.
- They recorded six species of bumble bees gathering
pollen from red clover flowers. Of these, more than 92%
consisted of B. vosnesenskii, indicating that it is the key pollinator
in Oregon.
- 25 more species of native solitary bees, belonging to 12 genera and five families, were collected in the bee traps.
Research Findings
The study has not only documented a great diversity of native bees in synchrony with red clover bloom, but it has also found that seed set was uniform and high across four fields. Under current pollinator regimes, researchers believe red clover seed production is close to its maximum in Oregon.
Solutions for Pollination
"To sustain
these high yields in Oregon, we must
- Conserve the habitat of bees,
- Use
pesticides judiciously and
- Provide floral resources prior to red clover bloom
Oregon State University entomologist Sujaya Rao, one of
the researchers on the study, concluded, "Globally, where red clover seed is
produced, similar studies are needed. If seed set is found to be well
below the maximum, appropriate alternative options such as augmentation
with commercial bumble bees could be considered."
Research is
ongoing at Oregon State University to determine whether high yields can
be achieved by native pollinators alone. If so, European honey bee hive
rentals would not be required, and this could lead to more economic red
clover seed production in Oregon.
The Crop Science Society of America (CSSA), founded in 1955, is an international scientific society comprised of 6,000+ members with its headquarters in Madison, WI. Members advance the discipline of crop science by acquiring and disseminating information about crop breeding and genetics; crop physiology; crop ecology, management, and quality; seed physiology, production, and technology; turfgrass science; forage and grazinglands; genomics, molecular genetics, and biotechnology; and biomedical and enhanced plants.
SOURCE: ©2009 Newswise, Inc
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