out of the cocoons and through the mud plugs. The females, which are almost always in the inner cells of the tunnel, emerge several days later. One or two weeks may be required for all the bees to emerge during cool weather.
Females mate soon after emerging and begin nesting in 3 to 4 days. The bees forage on a number of different flowers. In wooded areas, they seem to prefer ballhead waterleaf. In urban areas, dandelion and Oregon grape are commonly visited, in addition to cherries and apples.
The mason bee is non-aggressive and will sting only if handled roughly or if it should get trapped under clothing. It is less objectionable than the honey bee as a pollinator in urban areas and should be encouraged. Efforts are being made experimentally to develop large populations of these bees to use as a supplement to honey bees for fruit pollination, much as the alfalfa leaf cutting bee was developed for alfalfa seed pollination.
Populations for pollinating around a home or commercial orchard can be developed by establishing trap nests to collect the bees. Trap nests can be made by drilling holes 1/4 to 3/8 inches in diameter and 3 to 6 inches deep in pine or fir 4x4's. A "brad-point bit" leaves a nice, smooth hole. (Figure 57) Alfalfa leaf cutting bee boards with hole diameters of at least 1/4 inch can also be used. These boards are then attached to a house or other structure where bees have been seen. Some protection from rain is desirable. Boards can also be placed on dead trees or posts in wooded areas near streams where there is a good supply of mud for nest construction and wild flowers on which to forage.
Predrilled Drilled Block Infested with Mason Bees. Image Courtesy of Red 58bill.
Boards should be positioned where they will receive morning sunlight and started in March before the bees begin nesting and remove them in early to mid-summer when nesting is completed. If the boards are stored outdoors over winter (under cover to protect them from rain and snow) the bees will usually emerge in March and April. They should forage for pollen during the period of cherry and apple bloom and afterwards, if sufficient other flowers are available to them.
For large populations for orchard pollination, the nests should be under humid refrigeration at 35 to 40° F. This will permit control of emergence time and reduce predation and parasitism by the insect enemies of the bees. Do not place the nests in storage until September or October to assure complete development of the adults. The following spring, place the boards in the orchards in plywood shelters facing east to catch the morning sun. To hasten emergence, incubate the boards at room temperature for 24 hours before placing the bees in the orchard. The boards and some new nesting material should be in place a few days before apples begin to bloom, or earlier if other fruit bloom such as cherries, is available. Provide 500-1000 filled holes per acre. These should contain 750-1000 females, assuming an average of 1 1/2 females per hole. Males also visit flowers, but they do not live long and are not as effective as pollinators. Competing flowers such as dandelions should be mowed as soon as the fruit begins to bloom.
Developing large populations of the bees may be a slow process under orchard conditions; the short duration of bloom does not allow the bees to accomplish maximum reproduction. The orchard mason bee also has a tendency to fly away rather than using or reusing nests in the near vicinity. However, relatively large populations have been developed in 2 or 3 years in urban situations. Once established, orchard bees will nest in containers filled with large-diameter drinking straws or paper tubes folded in half.
Orchard Mason Bee, Osmia lignaria. This is a megachilid bee that as do other mason bee makes nests in reeds and natural holes, creating individual cells for their brood that are separated by mud dividers. They are unlike carpenter bees in that they cannot drill holes in wood. O. lignaria is a common species used for early spring fruit bloom in Japan, Canada, and t