Raspberries, blackberries, dewberries, cloudberries, and their kin belong
to the genus Rubus of the rose family (Rosaceae).
Some varieties will form fruits without floral visitation, but in all
cases, fully sized fruits only result from floral pollination by bees.
Raspberries and to a lesser extent blackberries are attractive to diverse
bees, as their abundant pollen and nectar is readily accessible at the
Fruits of raspberries and blackberries are compound drupes composed of
small turgid drupelets, each of which contains 1-2 seeds. Wild species
vary with regard to self-incompatibility, but flowers of domestic species
and their hybrids are hermaphroditic, self-fertile and to a degree self-pollinating.
Some, like the red raspberry, possess pseudogamous apomicty, meaning that
fertile seeds form without fertilization, but to form the fleshy tissue
surrounding the seed, fusion with male gametes is required. Each
flower consists of ring of stamens centered around a central brush of pistils
setting atop a receptacle. Stigmas of outer pistils can contact the
ring of anthers by themselves, but inner ones do not reach the distance.
Fruits from unvisited flowers thus consist of a ring of plump drupelets
surrounding a central pithy tip of leathery undeveloped drupelets.
Such fruits weigh 1/3 less and are unsuitable for fresh market sales.
Fully formed fruit (far left) that has been well
pollinated, and poorly formed fruit (center and right)
due to inadequate pollination
Fully formed fruits result from bee pollination of flowers. Flowers
of many cultivars provide generous rewards of pale gray or tan, protein-rich
pollen and accessible, often copious quantities of nectar. Superior
pollinators will atop the central column of pistils as they forage, assuring
that the stigmas of these inner pistils receive pollen. Poor pollinators
will stand on the petals instead, circling the flower for nectar and failing
to contact the innermost pistils.
Honeybees can be satisfactory pollinators where weather during bloom is
warm and conducive to flight.
At the Bee Lab, Dr. Jim Cane is studying a promising species of West Coast
Osmia that avidly visits all flowering raspberries and all varieties of
blackberries, consistently making stigmatic contact on every visit.
It is proving to be manageable in foam nesting boards used for alfalfa
Current experiments involve optimizing nest management in commercial cane
crops to increase populations now obtained from trap-nesting.
|This pretty bright green metallic bee named Osmia aglaia, is a good pollinator for berries in the Pacific Northwest.
||Nesting of this bee can be enhanced by providing shelters and nesting
boards. This nesting board was made using nesting boards for the
alfalfa leafcutting bee. Two boards are stacked together to produce
a hole that is twice as deep as the standard for the alfalfa leafcutting
bee. For more information about this shelter, view the
American Bee Journal - July 2006 article.
Photo Credits: Steve Werblow, Homestead Magazine