Abstract:
Farmers rely almost exclusively on the imported European honeybee (Apis mellifera L.)
for fruit and vegetable crop pollination services. The recent decline in honeybee health
has underscored the danger of relying on a single species to provide vital services.
Increasing pollinator biodiversity with native bees may provide biological insurance
against the decline of any particular species. By examining cropping systems, it is
possible to determine which native bees are providing pollination services and then
augment habitat to increase their numbers or attempt domestication. In this study, we
examined the native bee populations in the cranberry growing area of southern coastal
Oregon in order to determine if native bees play a significant role in cranberry
pollination. This two-year study surveyed four farms across a 22 km north-south
gradient. At least 27 bee species were observed during cranberry bloom (mid-May to
late June), of which five were observed foraging on the cranberry flowers. The imported
European honeybee and bumble bees (Bombus spp.) comprised 99.7% of foragers.
While honeybees and bumble bees foraged at comparable wind speeds, Bombus spp.
foraged at significantly lower average temperatures (P<0.0001). Both honeybees and
bumble bees collected cranberry pollen while foraging, but 37.2% of honeybees were
observed nectar-robbing (collecting nectar but no pollen) versus only 11.3% of bumble
bees. Bumble bees in general, and the western yellow-faced bumble bee (Bombus
vosnesenskii Radoszkowski) in particular, are abundant native pollinators of cranberry,
and may provide adequate pollination for small Oregon cranberry farms. Conservation
of bumble bee habitat and development of managed colonies will help maintain
pollination services.
