l 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 bee efficiency. The stamen (the structure holding the anthers) of alfalfa flowers is held under tension by two flower petals, and springs forward with force when released by a visiting bee. This triggering discourages many bees, including honey bees, which learn to avoid being hit by the stamen by approaching the flower from behind, where they can gather nectar but not pollen. The alkali bee (Nomia melanderi), a native ground-nesting megachilid bee, is not discouraged by this unusual flower structure and is a major pollinator of alfalfa seed in some western states. It has been used as an effective pollinator of alfalfa when grown for seed in the western United States. In this case large areas of barren soil are provided for the nesting of this bee,
Mason Bees. These are a gentle beneficial insects that has potential as a pollinator of apples, cherries, and other tree fruits. It is found throughout most of North America, particularly in wooded areas but often around homes in towns and cities.
Mason Bees. Image C