Mason bees and fruit trees share a two-way street


For mason bees, the wait for their first meal is a long one, six months if it’s a day.

There’s no TV, no smart phone, not even a book to while away the time as these solitary bees hang out in their tight cocoons waiting for the cool temperatures of early spring to break them out of lethargy, to convene at the floral banquet waiting for them among the branches of fruit trees.

And because honeybees and other pollinators haven’t made an appearance yet, there’s more sweetness for the native mason bees.

“Mason bees fill a spot in the season when other pollinators like honeybees are not out,” said Brooke Edmunds, a horticulturist with Oregon State University Extension Service. “They’re really important for fruit trees, especially in cool, wet areas.”

After emerging in March – perhaps February this year because of the mild winter — the small, bluish bees start foraging for food for the next generation and combing for suitable nesting sites.

“They’re solitary, non-aggressive bees, so they’re very different from honeybees; they don’t form hives,” said Edmunds, author of the new OSU Extension publication Nurturing Mason Bees in Your Backyard in Western Oregon.

Instead, mason bees, most commonly the native blue orchard mason bee (Osmia lignaria), look for cracks and crevices that fit their need for small spaces where they crawl in and lay eggs. They might find the appropriate spots in wood bored by other insects, siding on buildings or nesting blocks filled with tubes provided by gardeners.

“Gardeners can purchase cocoons containing adult bees as a way of introducing new mason bee populations to their yards,” Edmunds said. “Unfortunately, most garden centers and mail-order sources are probably sold out by now. But you can buy nesting houses and tubes any time. Place these in your garden and you might get lucky and they could nest in them this year.”

To hedge your bets, provide what mason bees need. Fill homemade or purchased nesting houses with cocoons in late winter or spring. You can get elaborate and remove the cocoons each fall, clean them of frass and mites, store them in the refrigerator over winter and reinsert them in the tubes in spring. Or choose the easy way; hang the tubes and wait for the bees to find them. Instructions for both methods are included in Edmunds’ guide.

By far the mason bee’s preferred food comes from early-blooming fruit trees like apples, pears, plums and cherries. So plant one or two. If you’ve got a small lot, choose columnar or dwarf cultivars.

Though not as dear to the bee’s palate, other plants qualify to attract them. Look to crabapples, flowering currant, elderberry, huckleberry, forsythia, pieris and Oregon grape. They’ll head straight for dandelion, Edmunds said, which are in good supply this time of year.

Since mason bees travel only short distances, about 200-300 feet, their favorite plants need to be planted near to nesting spots or away they’ll go. You’ll also need to provide small patches of clay mud, something in abundance in the Willamette Valley. But if you’ve covered your soil with mulch, it’s a good idea to push away a little bit to create a mud pool for them. If the soil dries out, give it a misting. Alternately, put a tray out and fill it with moist clay soil.

The female mason bees use the clay soil to wall up their eggs, which are deposited in the tubes or crevices with nectar and pollen they’ve rolled into little balls, Edmunds explained. They’ll continue to alternate wall, food, egg and wall until they come to the end of the tube or crevice and then wall it up for the next eight months. The eggs develop into small larva that spin cocoons where the adults form. Come spring when temperatures rise to 50 to 60 degrees, the adults break through the cocoon, chew through the clay and fly out to start the process all over again.

In their short three-month life, these single-minded bees do an important job for gardeners. Most significantly they efficiently pollinate prized fruit trees, giving a markedly increased yield. But consider a more altruistic reason, Edmunds said. Mason bees, like other beneficial insects, help diversify the garden, leading to a healthier backyard ecosystem, healthier humans and a healthier planet.

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