Cavity-Nesting Bees: Are Simple Habitat Solutions Useful for Bee Conservation?

Figure 1: This bee (Megachilidae: Megachile) lives in above-ground cavity-nests that can be easily constructed from materials found at the hardware store. Bees from the Megachile genus, often called leafcutter bees, have been sustainably managed for alfalfa pollination in eastern Washington, but little is known about the wild leafcutter bees in the Puget Sound Region.
Figure 1: This bee (Megachilidae: Megachile) lives in above-ground cavity-nests that can be easily constructed from materials found at the hardware store. Bees from the Megachile genus, often called leafcutter bees, have been sustainably managed for alfalfa pollination in eastern Washington, but little is known about the wild leafcutter bees in the Puget Sound Region.

Nests are essential for the reproductive success of bees (Almeida 2008). These nests provide shelter for developing immature bees, and protection from the environment. The vast majority of bees are solitary, creating burrows in a substrate and dividing this burrow into individual brood cells. Brood cells then contain an individual egg, which will hatch into a larvae, and feed on a pollen-nectar substrate before pupating. Adults from the previous generation usually do not come in contact with the next generation, and most immature bees receive no parental care beyond the pollen and nectar supplied for the larval stage.

Figure 2: Some bees do not collect exogenous materials like mud to partition their nests. The masked bees (Colletidae: Hylaeus) use a cellophane-like material produced internally by the Dufour’s gland to partition brood chambers. Masked bees like this one can be found in the Puget Sound Region, and are likely important pollinators.
Figure 2: Some bees do not collect exogenous materials like mud to partition their nests. The masked bees (Colletidae: Hylaeus) use a cellophane-like material produced internally by the Dufour’s gland to partition brood chambers. Masked bees like this one can be found in the Puget Sound Region, and are likely important pollinators.

Earthen burrows are quite common, with the vast majority of bees creating their nests in a soil substrate. Alternatively, a summary by Cane et al. (2007) indicates that linear nests in hollow or pithy stems, pre-existing tunnels left in wood by wood-boring beetles, and even snail shells can serve as habitat for bees that nest above the soil surface (Figure 1). Similar to soil-dwelling bees, bees that nest above the soil surface, hereafter cavity-nesting bees, partition the nest into individual brood chambers, sealing each cell with a variety of exogenous materials including, leaf tissue cut from nearby plants, leaf hairs, mud, resin, pebbles, or a combination of these materials (Figure 2) (Cane et al. 2007).

Figure 3: Not all bees are pollinators. Instead, some wild bees may be kleptoparasite, entering the nests of other bees, removing the original egg, and laying an egg of its own. This bee (Megachilidae: Coelioxys) has been found in our cavity-nesting structures, indicating a potential concern for the management of wild bees. Nest parasites are not uncommon. Anyone seeking to manage wild bees should also carefully monitor levels of parasites.
Figure 3: Not all bees are pollinators. Instead, some wild bees may be kleptoparasite, entering the nests of other bees, removing the original egg, and laying an egg of its own. This bee (Megachilidae: Coelioxys) has been found in our cavity-nesting structures, indicating a potential concern for the management of wild bees. Nest parasites are not uncommon. Anyone seeking to manage wild bees should also carefully monitor levels of parasites.

Knowledge of nesting habitat is essential to the conservation of wild bees, and the protection of their valuable pollination services. Few bees that nest in linear hollow stems have been sustainably managed, although there are likely many species that could be managed as agricultural pollinators. Preliminary results from our research indicate that the use of artificial nests may be one means to monitor and manage cavity-nesting bees in both the urban gardens and farmers of the Puget Sound Region (Figure 3).

If you would like to learn more about cavity-nesting bees, or work with us to monitor bee habitat in the Puget Sound Region, see our upcoming citizen science class the Pollinator Post Project.

 

References:

Almeida EAB (2008) Colletidae nesting biology (Hymenoptera: Apoidea). Apidologie 39:16-29.

Cane JH, Griswold T, Parker K (2007) Substrates and Materials Used for Nesting by North American Osmia Bees (Hymenoptera: Apiformes: Megachilidae). Ann Entomol Soc Am 100: 350-358.

Additional Reading:

Mader E, Spivak M, Evans E (2010) Managing Alternative Pollinators: A handbook for beekeepers, growers, and conservationists. SARE Handbook 11.

Image Credits:

Images were produced with the support of the Washington State Department of Agriculture (WSDA). For use, please contact the Northwest Pollinator Initiative.