tablishing 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 