Like the alfalfa leafcutter bee, mason bees belong to the family Megachilidae. As with other members of the Megachilidae family, mason bees use their large, scissor-like jaws to gather mud, pieces of leaf, or flower petals for the construction of their nests. All species of mason bee currently managed in the US belong to the genus Osmia. There are several hun-
Figure 6.1 Osmia sp. on flower.
dred members of the Megachilidae family in North America, and dozens of members of the Osmia genus (including both native and nonnative bees). Cur- rently only three species—Osmia lignaria, Osmia cali-
fornica, and Osmia cornifrons—are commonly avail-
able from commercial suppliers. Other Osmia species are managed regionally.
All Osmia are solitary, meaning that each female bee independently constructs her own nest, provi- sions the nest with pollen, and lays eggs. There is no queen, and the bees do not live together as a social unit like honey bees do. Female Osmia do not inter- act with other bees or with their own offspring after laying their eggs.
Many Osmia are gregarious, however, meaning that they have a tendency to construct their nests near each other—hence large numbers of bees can be housed in a single structure containing multiple nests. Many Osmia species will nest in manmade nests, however most species are difficult to domes- ticate because they are not gregarious. Male bees have no role in the construction or the provision- ing of nests. Upon their emergence as adults, males mate, then die soon thereafter. While they may feed on small amounts of flower nectar to maintain their own energy, male bees do not actively collect pollen, and have little value as pollinators.
Most native Osmia are 9/32 to 19/32 inch in length (~7 to 15 millimeters) with male bees noticeably smaller than females. The majority of North Ameri- can species are metallic blue, black, or green in color although other color variations exist. All female
Osmia have parallel rows of pollen collecting hairs,
called the scopa, on the underside of their abdomen. Female bees also typically have a pair of horn-like projections on the lower face. Male bees do not have facial horns, but often have longer antennae and a distinctive tuft of white hair in the center of their face (figure 6.2).
Despite having a stinger, female mason bees are not aggressive and rarely sting, even when handled. The sting is also much less painful than that of a honey bee. As a result beekeepers do not need any special protective equipment when working with
Osmia. Male bees have round abdomens with no
scopa or stinger (figure 6.3).
The most commonly managed mason bee, Osmia
lignaria, is a temperate species native to most west-
ern states from southern Alaska south to California and eastward to Texas and Montana—and to most eastern states from Maine south to northern Geor- gia. The eastern and western bees comprise two dis- tinct subspecies Osmia lignaria propinqua in the West, and Osmia lignaria lignaria in the East. Few records of the bee exist in the central plains states, prob- ably due to an absence of suitable nesting habitat, although intermediate forms between the two sub- species have been reported.
Osmia lignaria is commonly called the Blue Orchard
Bee, or “BOB” for short. Female BOBs are roughly the size of honey bees, although rounder in shape and metallic blue (figure 6.4, page 56). Male BOBs are similar but smaller with the characteristic tuft of white facial hair common to many Osmia species. BOBs are univoltine, meaning only one generation of
Figure 6.2 Like males of other mason bees, Osmia aglaia have a white patch of hair on the front of the face, and longer antennae.
Figure 6.3 Size comparison from left to right: Osmia atriventris (female), O. cornifrons (male), O. cornifrons (female), O. lignaria (male), O. lignaria (female), O. lignaria (female), Apis mellifera (female).
Mace Vaughan
offspring is produced each year. Currently, only the western subspecies of the BOB is commercially avail- able from bee producers.
The second most commonly managed mason bee, Osmia cornifrons, or the hornfaced bee, is origi- nally native to Japan. It was purposefully imported in the 1970s as a managed pollinator by the USDA Bee Lab in Beltsville, Maryland (see sidebar, below). Hornfaced bees are slightly smaller than the native BOB, and unlike many native Osmia, are brown in color with a striped abdomen and yellow scopa (as opposed to metallic blue or green). Like the BOB, the female hornfaced bee has a pair of horn-like prongs
Figure 6.4 A female blue orchard bee (Osmia lignaria) closes the entrance to her nest with mud.
Mace Vaughan
W
hile the hornfaced bee is typi- cally associated with tree fruit production, its potential on other crops is only recently being appreci- ated by a handful of people. Dr. Todd West, an assistant professor of hor- ticulture at West Virginia University (WVU) is one of them. With sup-port from USDA-SARE he has initiated an ambitious project that is introducing the bee to an entirely new group of fruit growers.
“Hornedfaced bees have the potential to be very useful and sustainable pollinators for blueberry pro- duction by small farmers in the Northeast Region of the US,” says West. “As compared to honey bees, which require year-round maintenance, the horn- faced bee requires minimal input and management. The hornfaced bees are only active for six to eight weeks from April to June which coincides with blue- berry blossom time.”
As part of the program over 300 blueberry grow- ers have been surveyed, and some will be provided with hornfaced bee cocoons and all of the necessary materials for management. The likes, dislikes, suc- cesses, and failures of those growers will be tracked and recorded over a two-year period. “Growers need to understand how to properly manage the bees and that the management practices are different than those of the honey bee,” he says.
So far the results have been promising. “Initial research trials in West Virginia indicate that popu-