ently than honeybees. These leafcutter bees are provided with predrilled "bee boards" that they use for nest construction. At the end of the season, the nest cells with developing bees are collected and carefully stored, to be released the subsequent season when alfalfa blooms.
Figure 53. Alfalfa Leaf Cutting Bee Pollinating Alfalfa.
Commercially produced bee blocks, consisting of a wood block drilled with a series of dead-end holes, are now widely available. These types of bee nests were initially developed in the 1960s by alfalfa seed producers in the western United States to attract and manage large numbers of the non-native alfalfa leafcutter bee (Megachile rotundata). Their sole purpose is to attract wild populations of these bees.
Bee Block for Attracting Large Population of Alfalfa Leaf Cutting Bees.
More recently they have been modified to manage the blue orchard bee (Osmia lignaria), a bee that is active only in the spring and will not pollinate later-flowering fruits and vegetables. Consequently, all of the nest tunnels are a uniform size and depth, which may be either too large or too small for many other species. Nest blocks with a greater diversity of hole sizes and depths are necessary to attract a variety of bees that are active throughout the year.
Under the best circumstances these nests can attract large numbers of cavity-nesting bees and boost their local populations. However, because these nests concentrate bee populations in unnaturally large numbers in a small space, they can become infested with parasites and disease spores after several seasons.
Without regular sanitation or the phasing out of nest materials, these parasites and diseases threaten long-term pollinator health wherever they are used. Because contaminated nest blocks left unattended in the landscape continue to attract wild bees from the surrounding area, they have the potential to do harm. Only with proper management can these nests maintain healthy bee populations indefinitely.
Alfalfa flowers provide an example of native be