Mason bee nests in the orchard of Robert Schreiber at Poysdorf, Austria, pictured during an International Fruit Tree Association tour
Growers should think not about species of beneficial insects, but develop strategies, such as insectaries, to benefit the whole community of natural enemies and pollinators, advises Paul Jepson, director of the Integrated Plant Protection Center at Oregon State University, Corvallis.
“We have a wonderful array of organisms to exploit by these tactics,” he said during a recent workshop on habitat and conservation practices for beneficial insects on farms.
Some natural enemies, such as beetles and spiders, are resident on the farm, and the goal is to not disrupt them. Others, such as hoverflies, lady beetles, and parasitic wasps, move from field to field and the objective is to attract them to the farm while they are moving about the landscape looking for something to forage on, he said.
Matthew Shepherd, senior conservation associate with the Xerces Society for Invertebrate Conservation in Portland, Oregon, said bees are the most important pollinators because they actively transport and collect pollen, but other insects, including butterflies, moths, wasps, beetles, and flies, can serve as pollinators when they visit flowers to feed or lay eggs.
There are 4,000 bee species in North America, of which there are about 600 in Oregon and Washington’s Columbia Basin.
Social bees, such as honeybees and bumblebees, collect pollen and take it back to their nests for their offspring. They are very effective pollinators because they are consistently working the flowers in an area around their nest and tend to work on a single species of flower. They can visit up to 150 flowers in one foraging trip, and there’s little possibility that they will take the wrong pollen to a flower, whereas butterflies will fly from one species of plant to another. Honeybees are also a convenient pollinator because they can be transported into the orchard in hives and don’t need habitat.
Common wild native bees, which include the mason bee, mining bee, sweat bee, bumblebee, longhorn bee, and leafcutter bee, can also play a significant role in agriculture, said Shepherd. Solitary bees nest in the ground or in cracks or crevices in walls, or in wood. Areas with a range of flowers that are in bloom for much of the year will draw bees to the orchard. “The amount of the landscape that’s in natural areas has a big influence on whether you get pollinators in your crop or not.”
Mason bees make nests in reeds and natural holes, creating cells for their brood that are separated by mud dividers. To attract mason bees, growers can provide wooden bee homes with 5/16-inch diameter holes to serve as nesting tunnels. Straws can be inserted in the holes as liners so that they can be replaced each season. The bees also need a source of water in order to make mud.
Mace Vaughan, director of the Xerces Society’s agricultural pollinator conservation program, said that if a grower wants to manage mason bees as a pollinator, they need the same level of management as honeybees. The grower should know how to clean out the tunnels and get rid of the diseased cocoons in the winter.
Shepherd cited studies conducted by U.S. Department of Agriculture researchers in Utah that showed that average cherry production in cold areas was much higher in orchards where mason bees were used for pollination than where honeybees were used. One reason mason bees are so efficient is they are active at low light levels and low temperatures and will fly on cold spring days when honeybees prefer not to. Mason and honeybees also differ in the way they carry pollen. The mason bee, which looks similar to a housefly, has a hairy abdomen and carries pollen on the lower part of its body, where it brushes off onto the anther and stigma of the flowers. A honeybee, in contrast, carries pollen as a wet lump on the back of its legs.
It takes fewer than 750 mason bees to pollinate an acre of orchard versus 20,000 to 30,000 honeybees, Shepherd said.
For more information, check the Web site at www.xerces.org/bees.