Make a nesting block
Many bees make themselves at home in holes drilled in wood blocks.
To make a nesting block, you'll need a piece of wood at least 4 inches deep and 8 inches long. Use untreated lumber and avoid cedar, which is toxic to insects.
Drill a grid of holes varying from 3/32 to 3/8 inch in diameter, spacing them approximately ¾ inch from each other. Drill deep holes, even going all the way through the block, to maximize the nesting depth.
Attach the block to a backing board and install a sloping roof that extends in front of the block to shelter the holes from the elements. Mount the backing board on a sturdy fence, post, tree, or building in a site where the holes will get only gentle morning sun.
You can buy a ready-made nesting block for orchard mason bees from Planet Natural ($18; 800/289-6656). Or try the Countryside Culture Mason Bee Block House, Northwest Nature Shop; 877/482-3241.
Encourage native bees ― and gather information about them ― this summer by participating in the Great Sunflower Project. Get free seeds, and help map pollination all over the country. Go to Great sunflower.org for details.
Among the many problems with chemical controls is that they are nonselective: They don't just kill pest insects, they kill bees too.
Instead of using pesticides, provide a rich array of native plants to attract beneficial insects like lacewings and lady beetles, which devour aphids, mealybugs, and whiteflies.
The Xerces Society (503/232-6639), a nonprofit organization working to protect bees and other invertebrates, is a great source of additional information, especially its Pollinator Conservation Handbook (2003; $23, including shipping), written in association with the Bee Works and illustrated with revealing close-up photos of bees, butterflies, and other pollinator insects.