{"id":520,"date":"2010-05-27T09:30:16","date_gmt":"2010-05-27T13:30:16","guid":{"rendered":"https:\/\/extension.umaine.edu\/blueberries\/?page_id=520"},"modified":"2025-09-09T15:55:15","modified_gmt":"2025-09-09T19:55:15","slug":"management-osmia-bees","status":"publish","type":"page","link":"https:\/\/extension.umaine.edu\/blueberries\/resources\/pollinator-insects\/management-osmia-bees\/","title":{"rendered":"301-Field Conservation Management of Native Leafcutting and Mason Osmia Bees"},"content":{"rendered":"

Fact Sheet No. 301, UMaine Extension No. 2420<\/strong><\/p>\n

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Fact Sheet Prepared by C. S. Stubbs, Assistant Scientist;\u00a0 F. A. Drummond, Associate Professor; and D. E. Yarborough, Extension Blueberry Specialist, The University of Maine, Orono, ME\u00a0 04469. March 2000.\u00a0 Acknowledgment: Research for this Fact Sheet was in part funded by Sustainable Agriculture Research and Education (SARE) Producer grants awarded to S. E. Kelly and R. Hammond.\u00a0 Photo Credits: Figure 1 Photo, L. Mayer and A. Stubbs; Figure 2 Photo, S. L. Allard; Figure 3 Photo, L. Mayer and A. Stubbs; Figure 4 Drawings, K. Bosse’.<\/em><\/p>\n

Introduction<\/strong><\/h3>\n
\"Top<\/a>
Figure 1:<\/strong> Top view of the male (left) and female (right) Maine blueberry bee, Osmia atriventris.<\/figcaption><\/figure>\n

Native leafcutting and mason bees, collectively called megachilids (pronounced mega kyle’ lids), are important pollinators of blueberry and cranberry, Vaccinium spp., in Maine.\u00a0 Field and flight cage studies conducted at the University of Maine have shown that the leafcutting Maine blueberry bee (Osmia atriventris;\u00a0 pronounced\u00a0 0z’ mee uh\u00a0 Ah truh’ ven tris), is an excellent pollinator of wild blueberry.<\/p>\n

Figure 1 shows the male and female Maine blueberry bee. Pollen collecting megachilid females are easily recognized as they are the only bees that carry the pollen on the underside of their abdomen.\u00a0 Megachilids, which literally means “big jaws,” get their name from the fact that they have strong jaws for cutting leaves and other plant material or for digging or collecting mud.\u00a0 The females use this material in the construction of nests for their offspring.<\/p>\n

Unlike honey bees and bumble bees, megachilid bees are solitary so they do not live in colonies.\u00a0 Thus each female needs her own nest sites.\u00a0 In nature, females nest in such places as raspberry and blackberry canes, sumac, and in the holes made by other insects in dead trees and wooden fences.\u00a0 There are not enough natural nest sites, which limits the size of their populations.\u00a0 Our research has shown that you can increase megachilid bee numbers in your blueberry fields by providing them with wooden blocks for them to nest in. Figure 2 shows Osmia on a wooden bee nesting block.<\/p>\n

\"Wooden<\/a>
Figure 2:<\/strong> Wooden bee nesting block with Osmia spp. and completed nest capped with a masticated (thoroughly chewed) leaf plug.<\/figcaption><\/figure>\n

Note the lower left tunnel in Figure 2 is sealed with a leaf plug, which indicates a completed nest.\u00a0 Bee conservation is becoming increasingly important, particularly as the price of commercially available pollinators increases.<\/p>\n

This Fact Sheet will provide information on Osmia biology and two important ways you can conserve and increase their populations. First, you can encourage the growth of certain plants along field borders.\u00a0 Second, you can construct and set out wooden bee nesting blocks.<\/p>\n

Description and Biology<\/strong><\/h3>\n

In Maine, the megachilids important in pollinating blueberry all belong to the genus Osmia. Throughout the wild blueberry growing regions of Maine, nine different species of Osmia that pollinate wild blueberry have been reared from wooden nesting blocks. Seven species, including\u00a0Osmia atriventris, are leafcutting species, which cap their nests with masticated (thoroughly chewed) plant material. The other two Osmia species use mud to cap their nests and hence are known as mason bees.<\/p>\n

\"Four<\/a>
Figure 3:<\/strong> Four species of Osmia bees that pollinate blueberry. From left to right: Osmia atriventris (Maine blueberry bee), O. inermis, O. lignaria, and O. inspergens.<\/figcaption><\/figure>\n

The species found in Maine generally are some shade of metallic blue. The only exception is Osmia inermis, which is a nonmetallic black.\u00a0\u00a0 In Maine, the species range in size from 1\/4 to 2\/3 inch (7 to 16 mm).\u00a0 Figure 3 shows several species of Osmia bees. Osmia over-winter as dormant adults. Beginning in late April, they begin to emerge from their nest sites.<\/p>\n

Males typically emerge before females and are smaller than females.\u00a0 Mating occurs from early to mid-May.\u00a0 In coastal and more northern inland growing areas, emergence and mating may continue until late May.\u00a0 In general, the adult pollinating season of these bees occurs at the same time as blueberry bloom.<\/p>\n

Female bees will begin nest construction several days after mating. Often their overwintering site of emergence is reused.<\/p>\n

When females collect nectar and pollen from wild blueberry flowers for provisioning their nests, they pollinate the crop. Males contribute slightly to pollination when they visit flowers for nectar, but males do not collect pollen or assist in nest construction.<\/p>\n

Female Osmia lay a single egg on a nectar-pollen loaf-shaped provision, then seal the cell with a thin partition of masticated plant material or mud. It takes from 11 to 20 trips to blueberry flowers to complete one cell. A single female may lay as many as 32 to 35 eggs.\u00a0 Eggs hatch into larvae which feed on the nectar-pollen provision in their cell. They then go through a nonfeeding pupal stage and by mid-fall have developed into dormant adults which will then emerge the following spring.<\/p>\n

Parasites, predators, and disease can reduce the number of adults emerging the following season.\u00a0 For example, adult female parasitic Sapyga (sa pi jah’) wasps may enter uncapped nests and lay their eggs, which develop faster than Osmia. The wasp larvae kill the developing bees.<\/p>\n

Plants to Encourage Along Blueberry Field Borders<\/strong><\/h3>\n

Encouraging the growth of certain plants along your field borders will conserve and enhance Osmia populations.<\/p>\n

Because some Osmia emerge a bit earlier than blueberry bloom and some live longer than blueberry bloom, the bees will need additional sources of nectar and pollen in order to achieve good reproduction.\u00a0 Females also need young, tender deciduous leaves for nest construction. Our research has found that the plants listed in Table 1, when found along field border, will increase Osmia numbers in your field.<\/p>\n\n\n\n\n\n\n\n
Table 1. <\/strong>Recommended forage plants for enhancing\u00a0populations of Osmia spp.<\/td>\n<\/tr>\n<\/thead>\n
Common name<\/span><\/strong><\/td>\nGenus<\/span><\/strong><\/td>\nCommon name<\/span><\/strong><\/td>\nGenus<\/span><\/strong><\/td>\n<\/tr>\n
Before and during blueberry bloom<\/td>\nDuring and\/or after blueberry bloom<\/td>\n<\/tr>\n
birch
\nmaple
\noak
\npoplar, aspen
\nwillow<\/td>\n		Betula
\nAcer
\nQuercus
\nPopulus
\nSalix<\/td>\n		aster
\ncherry
\ndogwood, bunchberry
\nhoneysuckle
\nsheep laurel, lambkill<\/td>\n		Aster
\nPrunus
\nCornus
\nLonicera
\nKalmia<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Construction, Placement, and Maintenance of Wooden Bee Nesting Blocks<\/strong><\/h3>\n

Placing wooden bee nesting blocks around blueberry field borders is an effective, inexpensive means of increasing Osmia bees in your field.<\/p>\n

Materials needed.<\/strong> Wooden bee nesting blocks can be made from soft or hardwoods.\u00a0 Maple blocks last the longest and do not readily split, but cost more to make.\u00a0 We have had good success using pine and spruce 2 x 6s. The only other materials needed are metal 3\/4-inch strapping tape (also called plumber’s tape), screws for fastening the strapping tape to the back of the blocks, and nails to attach the wooden bee nesting blocks to tree trunks or stakes.<\/p>\n

Although using tree trunks involves less construction time and costs, there are two major advantages to attaching the wooden bee nesting blocks to stakes.\u00a0 First, our research indicates that more bee nests are made in wooden bee nesting blocks that are on stakes.\u00a0 Second, fewer nests by other insects and spiders are made in wooden bee nesting blocks on stakes.\u00a0 A relatively inexpensive alternative to tree trunks is to use 10-foot ceiling strapping, cut into 3.3-foot lengths or use saplings for the stakes.<\/p>\n

Bee nest block construction.<\/strong> Saw the 2 x 6 into 5-to 6-inch lengths.\u00a0 If, for example, you use 8-foot-long 2 x 6s and make 6-inch long wooden bee nesting blocks, you can get 15 wooden bee nesting blocks from each 2 x 6.<\/p>\n

Using a 5\/16-inch drill bit, drill 12 to 14 holes into the front of each block.\u00a0 Each hole, (or tunnel as they are called) should be drilled to a depth of 4.75 to 5.75 inches.\u00a0 Be careful not to drill completely through the block because the adult female bees will not nest in tunnels that are open at both ends.<\/p>\n

If you want to provide good nesting for the larger species of Osmia as well as for the Maine blueberry bee, we recommend that half of the tunnels in each nesting block be drilled with a 7\/16-inch drill bit.<\/p>\n

Also, larger blocks with more tunnels per block are not recommended because they are more noticeable to parasites and predators.<\/p>\n

Cut the plumber’s tape into 3-inch lengths.\u00a0 Screw the piece of plumber’s tape 1-inch from the top on the center of the back of the wooden bee nesting block.\u00a0 The tape should extend two inches from the top of the wooden bee nesting block.\u00a0 Careful not to screw through a tunnel!\u00a0 The design for the front and back of a completed wooden bee nesting block using two nest tunnel diameters is shown in Figure 4.<\/p>\n\n\t\t