by Bob Heath

With the noted decline in success of rearing honeybees, many growers and home gardeners have begun to worry about the reliability of counting on honeybees alone for pollination of their crops and gardens.  Besides the problems with maintaining hives of honeybees because of loss of habitat, pests and increased use of harmful pesticides, there are several other reasons to look beyond honeybees for adequate pollination of fruits and flowers.  Honeybees are good, but not great, pollinators of many flowers.  Their time per flower is longer than some bees, and there are bees that carry more pollen per visit than honeybees. Honeybees avoid pollinating members of the nightshade family (Solanaceae), which includes tomatoes, peppers, eggplants and potatoes. Honeybees avoid dim habitats (such as the edge of forests), become disoriented in greenhouses, and take the day off if it rains. Finally, honeybees aren’t fully active until May, although many flowering crops bloom from late March through April. For these reasons, many people are looking for native bee species for crop pollination. Bees that are gentle and easily handled are at the top of the list. Among the best of these native bees for use in Northeast Ohio is the blue orchard bee (Osmia lignaria).

The blue orchard bee (BOB, for short) is a member of the family of mason bees, so named because they lay their eggs in small chambers walled off with mud, just as a mason lays bricks separated by cement.  No queen bees here. As with most bee species, these are solitary bees that build individual nests rather than an organized social-colony hive headed by a queen.  BOB overwinters in a cocoon, emerging when temperatures reach above 55 degrees Fahrenheit for several consecutive days. The males emerge first, followed in a couple days by the females. The first thing the female BOB does is mate with one or two males. After mating, she spends several days sucking up nectar until her ovaries mature, then she gets down to business of building a nest. She will seek out a nesting site that is a tube-shaped cavity around six inches long and just the right diameter of 5/16 inch. When selecting a nest, the female BOB flies back and forth in front of the hole to make sure she can remember exactly where it is located. She also wants to be sure the correct type of mud–a silt-clay mixture moist enough to be balled up–is in the vicinity to pack into the nest.

She begins building the nest by carrying some mud in her mandibles and packing it at the back of the nest. Then she forages for pollen and nectar in nearby flowers, generally within 100 yards of the nest. BOBs prefer Rosaceae–flowers of the rose family, such as apples, pears, almonds and blackberries. The female BOB can visit as many as 75 flowers in one trip to provision the nest with a mix of pollen and nectar; it takes about 25 trips to provision one compartment in the nest. She flies from dawn until dusk, even if it’s windy or drizzly. When the compartment in the nest is sufficiently provisioned, she lays a fertilized egg and then closes the compartment with a dollop of mud. Next, she collects pollen and nectar for the next compartment, lays an egg and closes it off. She builds the nest from the back to the front but, as she approaches the front of the nest, she lays unfertilized eggs. Fertilized eggs become females, while unfertilized eggs become males; the sex ratio in BOBs is two females to three males. When the nest is complete, she walls it off with a dollop of mud, then begins the process all over again, seeking a new nesting site and so on. Inside the nest the eggs hatch. Each larva goes through three molts, then pupates and overwinters in the cocoon, hatching only when the weather turns from cold to cool the following spring.

Think about all the flowers the female BOB visits to complete one compartment of the nest: 75 flowers per trip x 25 trips per compartment = more than 1,800 flower visits, and there are about eight compartments per nest. And each female BOB builds several nests during her lifetime, which is only four to eight weeks long. Wow!! BOBs visit more flowers per minute than honeybees, and they collect more pollen per visit than honeybees, making them highly efficient, valuable pollinators. They are so valuable that a cottage industry has sprung up, selling mason bee “hotels,” which provide the right length and diameter for BOB nests. But wait, there’s more! You also can buy BOB cocoons and mason bee mud. Mud, cocoons and “hotels” can then be placed in an orchard or a flower garden. It has been noted that by encouraging BOBs into an orchard, crop yields can be noticeably improved. The blue mason bee is active early in the season, from late March through early June.

References:

Wilson, J.S., & Carril, O.M. (2016). The Bees in Your Backyard: A Guide to North American Bees. Princeton University Press. ISBN 978-0-691-16077-1

Wikipedia. Retrieved from https://en.wikipedia.org/wiki/Osmia_lignaria