Alternative Pollinators: Native Bees


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Alternative Pollinators: Native Bees

  1. 1. Alternative Pollinators: Native Bees A Publication of ATTRA—National Sustainable Agriculture Information Service • 1-800-346-9140 • www.attra.ncat.orgBy Eric Mader, Mace This publication provides information and resources on how to plan for, protect and create habitat forVaughan, Matthew native bees in agricultural settings. Creating and preserving native bee habitat is a good risk manage-Shepherd and Scott ment strategy for farmers of specialty crops such as almonds, apples, blackberries, blueberries, cherries,Hoffman Black cranberries, pears, plums, squash, tomatoes and watermelons. Oil and biofuel crops requiring bee pol-The Xerces Society lination include canola and sunflower. Even meat and dairy industries are dependent on bee pollinationfor Invertebrate for the production of forage seed such as alfalfa and clover. In many cases, these native pollinators are,Conservation on a bee-for-bee basis, more efficient than honey bees.www.xerces.orgPublished 2010 IntroductionContents W orldwide, there are an estimatedIntroduction ..................... 1 20,000 species of bees (Michener,Case study: Gardens 2000), with approximately 4,000of Goodness Farm .......... 2 species native to the United States (Win-Native bee biology ........ 3 free et. al., 2007). The non-native EuropeanNative bee habitat ......... 4 honey bee (Apis mellifera) is the most impor-Native bees as croppollinators ......................... 4 tant crop pollinator in the United States. However, because of disease and other fac-Assessing native beehabitat on farms ............. 5 tors the number of managed honey beePollinator-friendly hives in the United States has declined byfarming .............................. 6 50 percent since 1950 (NRC, 2007). DuringProviding alternative this same period, the amount of crop acre-forage ................................. 8 age requiring bee pollination has continuedCreating artificial to grow. This makes native pollinators evennest sites .......................... 11 more important to the future of agriculture.Common nativebees ................................... 17Case study:The alkali bee ................. 19 Mason bee on berberis. Photo byAppendix 1: Plants to USDA-ARS, Jack native bees .... 20Appendix 2: Additionalresources ......................... 23 Native bees provide free pollinationReferences ...................... 25 services and are often specialized for foraging on particular flowers, suchATTRA—National Sustainable as squash, berries or orchard crops.Agriculture Information Service This specialization results in more( is managedby the National Center for Appro- efficient pollination and the produc-priate Technology (NCAT) and is tion of larger and more abundant fruitfunded under a grant from theUnited States Department of from certain crops (Tepedino, 1981;Agriculture’s Rural Business- Bosch and Kemp, 2001; Javorek et. al.,Cooperative Service. Visit theNCAT Web site ( Mining bee carrying load of yellow pollen entering 2002). The pollination done by nativesarc_current.php) for nest. Photo by Matthew Shepherd, The Xerces Society. bees contributes an estimated $3 billionmore information onour sustainable agri- worth of crop production annually to the U.S.culture projects. economy (Losey and Vaughan, 2006).
  2. 2. Case study: Gardens of Goodness Farm Pollinator conservation is essential to Barb and Jim Lindemann’s Gardens of Goodness farm near Madison, Wis. As a diversified organic farm with more than 40 antique apple varieties, as well as peach, cherry and quince trees, blueberry and raspberry plants and numerous bee-pollinated vegetables, Gardens of Goodness has a highly varied abundance of crops blooming throughout the growing season. Gardens of Goodness has high pollination demands, but the farm is surrounded by miles of conventional corn and soybean farms and a small housing development of manicured lawns – hardly the best bee habitat. To compensate for their situation the Lindemanns have steadily improved their farm for bees by adding supplemental floral sources, enhancing nest sites and learning to farm without pesticides. The result is a farm that is always buzzing with the activity of countless wild bees as well as benefi- cial insects that help keep pest populations in check. On any given day during the growing season it is not unusual to see dozens of bee species on the farm. Bright metallic green sweat bees swirl around the berry crops, ground-nesting mining bees and wood-nesting mason bees fly among the fruit trees, and huge lum- bering bumble bees slowly move between the rows of tomato transplants. This abundance of bees is not by chance. The Linde- manns have taken several specific steps to encour- age bees. They added red clover, white clover and Siberian squill to the orchard understory to provide nectar and pollen before and after the fruit trees are in bloom. Also, non-aggressive weedsGardens of Goodness orchard. Photo by Eric Mader, The Xerces Society. like dandelion and violet are tolerated, resulting in a colorful, flower-rich ground cover. In addition to providing nectar and pollen for bees, these plants help trap the spores of apple scab (a fungal disease harbored in leaf litter) close to the ground where wind and rain cannot splash the spores up into the tree canopy and cause new infections. Nest sites for bees have been enhanced on the farm by providing nest blocks for mason and leafcutter bees. Naturally occurring patches of bare ground where ground-nesting bees might be present are maintained and plastic mulch is not used in the vegetable row crops. Because the Lindermanns have a diversity of crops and rotate their row crops regularly, pest popu- lations rarely reach problematic levels and pesticides are rarely needed. Apples, which are their largest crop, are processed into cider rather than fresh marketed so that minor cosmetic damage by pest insects can be tolerated. The Lindemanns make every effort to control the few crop pests that do occur with pheromone and sticky traps rather than chemicals. Even chemical fertilizers are unnecessary for the Lindemanns. Instead, they use a composted invasive lake weed, which they received free through a partnership with their local watershed district, as their main fertilizer. All of these practices, many of which began as attempts to conserve pollinators, have added up to a productive business with an enthusiastic community-supported agriculture (CSA) program and farm stand customer base.Page 2 ATTRA Alternative Pollinators: Native Bees
  3. 3. Native Bee BiologyNative bees come in a wide range of colorsand sizes, from tiny sweat bees less than aquarter of an inch long to bumble bees overan inch in length. While some of these spe-cies may look like the familiar image of abee with hairy yellow and black stripes, theymay also be dark brown, black or metallicgreen and blue, with stripes of many colors.Most are solitary, with each female creatingand provisioning her nest without the sup-port of a caste system of workers. Most areunlikely to sting (Shepherd et. al., 2003).The common names for native bees oftenreflect their nest building habits: miner, car-penter, mason or plasterer. Other names Related ATTRAdepict behavioral traits. For example, sweat Publicationsbees drink salty perspiration to acquire nutri-tionally important minerals. Farmscaping Snag with beetle tunnels now occupied for bee nests. to EnhanceAbout 70 percent of native bees excavate Photo by Matthew Shepherd, The Xerces Society. Biological Controlunderground nests (Potts et. al., 2005). Soli-tary bees dig narrow tunnels leading to a series the mother bee generally dies. Her offspring Organic IPMof brood chambers, each one provisioned with will remain in the nest, passing through the Field Guidea mixture of pollen and nectar and each hold- egg, larva and pupa stages before emerging Tree Fruitsing a single egg (Michener, 2000). as an adult to renew the cycle. Organic Production Overview For some species this life cycle may progress over a matter of weeks, resulting in a second Applying the Principles generation of bees in a single season. A few of Sustainable species may remain dormant for over a year. Farming Most solitary bees however complete this life cycle over the course of a full year. Native bees often only live for a few weeks as actively flying adults. They mate immedi- ately upon emergence and the females begin nesting. They lay relatively few eggs com- pared to other insects, with a single female often laying less than 50 eggs before sheMounds of excavated soil surround the entrance tobee nests. Photo by Eric Mader, The Xerces Society. dies. Male bees do not live long beyond mat- ing, they do not collect pollen and have little value as pollinators.About 30 percent of bees nest in wood tun-nels, usually pre-existing holes such as those While most of these wood-nesting andmade by wood-boring beetles, but some will ground-nesting bees are solitary, some arechew out the center of pithy twigs (Michener, gregarious, preferring to nest near others,2000). Females of these wood-nesting bees a behavior that allows large aggregations tocreate a line of brood cells, often using mate-rials such as leaf pieces or mud as partitionsbetween cells (O’Toole and Raw, 1999).In the case of both ground-nesting and Inside of reed stem showing pollen mass and eggs. Photo by G. Neuenswonder,wood-nesting bees, once the nest is complete, ATTRA Page 3
  4. 4. develop in favorable locations. Only a few tunnel and ground-nesting bee species ever develop truly social colonies, and often such behavior is environmentally dependent with some bees being social in one situation and being solitary in another (Michener, 2000). The one group of strictly social bees native to the United States is the group of approxi- mately 45 bumble bee species (Kearns and Thompson, 2001). Bumble bees live in a colony with a caste system of workers, males and a single egg-laying queen. Within this social structure, bumble bees share the labor of foraging and rearing their young. Similar to honey bees, bumble bees construct a wax comb; however, this comb is not a sym- metrical series of hexagonal cells, but rather is an abstract configuration of round wax pots, some containing brood and some containing Wildflowers planted to create on-farm habitat. Photo small amounts of pollen or nectar. by Katharina Ullmann, The Xerces Society. Bumble bees nest in cavities such as aban- doned rodent burrows, brush piles and grass a much shorter active period, often no more tussocks (McFrederick and LeBuhn, 2006). than five or six weeks, and have life cycles The colony grows through three or four gen- synchronized with the blooming of preferred erations and, depending on the species, may flower species. have several hundred workers at the peak in The two habitat components need to be mid-summer. Unlike honey bees, bumble close enough together so that the bees can bee colonies do not survive over the winter. fly between them. The fl ight distance of a bee varies with the size of the bee. Small Native bee habitat sweat bees and mining bees may not fly Habitat for native bees has two major com- more than 200 or 300 yards from nest to ponents: a place for the nest and flowers to forage area (Greenleaf et. al., 2007). Large forage. As detailed above, the bees (bumble bees, for example) can cross nest site can be bare ground a mile or more of inhospitable, flower-less or a snag. The flowers can be landscape to forage. But however large the native wildf lowers or non- bee, if it has to fly too far the effort begins native weeds. Most bees aren’t to outweigh the benefits and the bee may too choosy; if they can reach either fi nd somewhere else to nest or not the nectar or gather pollen, they survive in the landscape. can supply their nest. Some A third factor that influences habitat is insec- bees, however, are very choosy ticide exposure. To thrive, bees need minimal and will only gather pollen exposure to pesticides. from a small number of plant species. In extreme cases, the bee may be restricted to just a Native bees as single plant species. Social bees crop pollinators with a long-lived colony, such Among the food crops requiring bee pollina-Farm pond with snag and surrounding as bumble bees, need flowers tion are almonds, apples, blackberries, blue-vegetation. Photo by Mace Vaughan, The blooming throughout the sea- berries, cherries, cranberries, pears, plums,Xerces Society. son. Solitary bees usually have squash, tomatoes and watermelons. OilPage 4 ATTRA Alternative Pollinators: Native Bees
  5. 5. The reason for this increased efficiency is the mason bee’s greater tolerance for cold and wet weather. In addition, the foraging behav- ior is different in native bees than in honey bees. For example, individual honey bee workers specialize in the collection of either pollen or nectar. Nectar-foraging honey bees often never contact the anthers (pollen-pro- ducing structures) in apples, unlike mason bees that must collect both pollen and nec-Yellow-faced bumble bee on raspberry flower. Photo tar (Bosch and Kemp, 2001).by Mace Vaughan, The Xerces Society. Alfalfa flowers provide another example of native bee efficiency. The stamen (the struc- ture holding the anthers) of alfalfa flowers is held under tension by two flower pet- als, and springs forward with force when M released by a visiting bee. Th is triggering any discourages many bees, including honey native bees, who learn to avoid being hit by the sta- bee men by approaching the flower from behind, species are more where they can gather nectar but not pollen. effective than honey The alkali bee (Nomia melanderi), a native bees at pollinating ground-nesting bee, is not discouraged byYellow-faced bumble bee approaching tomato flower. this unusual flower structure and is a major flowers on a bee-for-Photo by Mace Vaughan, The Xerces Society. pollinator of alfalfa seed in some western bee basis. states (Mader et. al., 2010).and biofuel crops requiring bee pollinationinclude canola and sunflower. Even meat and Some native bees are highly efficient becausedairy industries are dependent on bee pollina- they specialize in one type of flower. Squashtion for the production of forage seed such as bees (genus Peponapis), for example, pri-alfalfa and clover. marily visit flowers from the squash family (Tepedino, 1981). Female squash bees oftenProducers of these crops should consider start foraging before dawn and the malesthe needs of native bees in their farm man- even spend the night in squash flowers.agement because these insects may provideincreasing yields and farm profit, and reduce Another efficiency of native bees is the pro-reliance on rented honey bees. Native bees cess of buzz pollination. Bumble bees inalso provide an insurance policy if rental particular are notable for their ability tohoney bees are prohibitively expensive or dif- grasp a flower and vigorously vibrate theirficult to obtain. fl ight muscles, releasing pollen from the anthers. This behavior is very important for some plants such as blueberries, cranberries,Native bee ef f iciency tomatoes and peppers, all of which releaseMany native bee species are more effective pollen from pores within the anthers (simi-than honey bees at pollinating flowers on a lar to salt being shaken from a salt shaker)bee-for-bee basis. For example, according to (Mader et. al., 2010).U. S. Department of Agriculture researchers,only 250 female blue orchard bees (Osmialignaria) are required to effectively pollinate Assessing native beean acre of apples. The is the equivalent ser- habitat on farmsvice of one to two honey bees hives, each Many growers may already have an abun-containing 15,000 to 20,000 workers (Bosch dance of habitat for native pollinators onand Kemp, 2001). or near their land. Having semi-natural ATTRA Page 5
  6. 6. natural habitat available blooming supply of f lowers necessary to significantly increases support resident pollinators. pollinator populations (Kremen et. al., 2004 Existing nest sites and Williams and Kre- Look for nest sites around the property. men, 2007). Linear hab- Nests of ground-nesting bees are likely to itats along field edges, occur in semi-bare patches of soil. Wood- hedgerows and drainage nesting bees will be in snags or shrubs with ditches offer both nest- soft-centered twigs (Michener, 2000). Bum- ing and foraging sites ble bees may be nesting in old rodent bur- (Carvell et. al., 2004). rows or brush piles. Woodlots, conservation areas, utility easements, Most bees are active on warm sunny days, farm roads and other from mid-morning through the afternoon. untilled areas may also Some, however, may be active early in the contain good habitat. morning (for example, squash bees), while Often, marginal areas others will continue flying late in the evening that are less fit for crops (bumble bees). Anywhere from one to thou- may be managed as pol- sands of bees may be present at a nest siteTrackside wildflowers provide useful habitat.Photo by Mace Vaughan, The Xerces Society. linator habitat (Moran- and they may be as small as a medium-sized din and Winston, 2006). ant (less than a quarter inch) to larger than a Here are some tips on honey bee (three-quarters of an inch). recognizing specific resources so that they In the case of ground-nesting solitary bees, can be factored into farm planning. the nest entrance will be visible only during the season the adults are active, the timing Existing plant composition of which varies from species to species. The When assessing pollen and nectar resources, nest entrances appear as small holes in the it is important to look at all of the plants ground, often with piles of excavated soil on and around a farm. These plants include around the entrance. In some cases, they insect-pollinated crops, as well as the flowers may resemble an ant nest, although often – even weeds – in buffer areas, forest edges, with a larger entrance hole. roadsides, natural areas, fallow fields and more. Insect-pollinated crops may supply Pollinator-friendly farming abundant forage for short periods of time. In addition to conserving the food and nest However, for pollinators to be most produc- sources of native bees, you can take an active tive, nectar and pollen resources are needed role in protecting bees through the adoption outside the period of crop bloom. of pollinator-safe farming practices. While As long as a plant is not invasive, consider let- insecticides are an obvious threat to bees, ting some of the native or non-native weeds other farm operations or disturbances such and wildflowers bloom. For example, dande- as burning and tilling can also cause harm. lions, clover and other non-native plants are often good pollinator plants in orchards. Minimizing pesticide use Keep in mind that small bees may only fly Insecticides not only kill pollinators (Johan- a couple hundred yards, while large bees, sen, 1977), but sub-lethal doses can affect their such as bumble bees, can forage a mile or foraging and nesting behaviors, often prevent- more from their nest (Greenleaf et. al., ing plant pollination and bee reproduction 2007). Therefore, taken together, a diversity (Thompson, 2003; Decourtye et. al., 2004; of flowering crops, wild plants on field mar- and Desneaux et. al., 2007). Herbicides can gins and plants up to a half-mile away on kill plants that pollinators depend on when adjacent land can provide the sequentially crops are not in bloom, thus reducing thePage 6 ATTRA Alternative Pollinators: Native Bees
  7. 7. amount of forage available (Kremen et. al., Spray drift presents another threat to for-2002 and Tscharntke et. al., 2005). aging native bees. Drift can occur either as spray droplets or vapors, as happens whenIn general, while pesticide labels may list a volatile liquid changes to a gas. Factorshazards to honey bees, potential dangers to affecting drift include temperature (includ-native bees are often not listed. For example, ing temperature inversions), wind, applica-many native bees are much smaller in size tion method, equipment settings and spraythan honey bees and are affected by lower formulation (Ozkan, 2000).doses. Also, honey bee colonies may be cov-ered or moved from a field, whereas wild Spray application methods and equipmentnative bees will continue to forage and nest settings also strongly influence the potentialin spray areas. for drift. Since small droplets are most likelyIf pesticides cannot be avoided, they should to drift long distances, aerial applicationsbe applied directly on target plants to pre- and mist blowers should be avoided. Stan-vent drift. Broad-spectrum chemicals should dard boom sprayers should be operated at thebe avoided if at all possible. In addition to lowest effective pressure and with the nozzlesactive ingredients, consider the formulation set as low as possible. For example, drop noz- I f pesticidesof pesticides; generally dusts and fine pow- zles can be used to deliver insecticide within the crop canopy where it is less likely to be cannot beders that may become trapped in the pol- carried by wind currents. Regardless of the avoided, theylen-collecting hairs of bees and consequentlyfed to developing larvae are more dangerous chemical or type of application equipment should be appliedthan liquid formulations (Vaughan et. al., used, sprayers should be properly calibrated directly on target2007). to ensure that excess amounts of pesticide plants to prevent drift. are not applied (Ozkan, 2000).Crops should not be sprayed while in bloom.Nighttime spraying, when bees are not for- Alternatives to conventional insecticidesaging, is another way to reduce bee mortal- include the use of selective products that tar-ity. Periods of low temperatures may also get a narrow range of insects, such as Bacil-be good for spraying because many bees lus thuringiensis (Bt) for moth caterpillars,are less active. However, the residual toxic- although even these products can be detri-ity of many pesticides tends to last longer mental when they drift. Other alternativesin cool temperatures. For example, dewy for some pests include bug vacuums, phero-nights may cause an insecticide to remain mones for mating disruption and kaolin claywet on the foliage and be more toxic to bees barriers for fruit crops. Several ATTRA pub-the following morning, so exercise caution lications are available to assist farmers with(Vaughan et. al., 2007 and Johansen and implementing non-chemical pest controlMayer, 1990). alternatives. See the ATTRA Biorationals: Ecological Pest Management Database, avail- able at, for informa- tion on specific product and pests. Finally, remember that many of the habitat features that support pollinators will also host benefi- cial insects that help control pests naturally, reducing the need for pesticides. Minimizing the impact of mowing, haying, burning or grazing Grazing, haying, mowing and fire can have damaging effects on pollinators (Black et. al., 2008). Historically, there were suffi-Calibrating sprayer nozzles. Photo by USDA-ARS. cient areas of diverse vegetation to ATTRA Page 7
  8. 8. nest sites of ground-nesting bees, tilling and flood-irrigating areas of bare or partially bare ground that may be occupied by nesting bees should be avoided (Shuler et. al., 2005 and Vaughan et. al., 2007). Grazing such areas can also disturb ground nests. And fumigants for the control of soilborne crop pathogens (such as Verticil- lium wilt), or covering large areas with plas- tic mulch can be detrimental to beneficial ground-nesting insects such as bees. Weed control alternatives to tillage that are safer for ground-nesting bees include the use of selective crop herbicides, flame-weedersContrast in vegetation due to grazing. Photo by Irv Cole, USDA-NRCS. and hooded sprayers for between row herbi- cide applications. populations of habitat specific pollinators. However, now that many of these areas exist Leaving patches of un-mowed grass in which only as fragments in larger agricultural land- rodents can nest will create future nest sites scapes, consideration of pollinators is needed for bumble bees. Bunch grasses tend to pro- to ensure healthy populations. vide better nesting habitat than sod-forming varieties. Structural landscape features such Studies suggest that less than one-fi fth of as brush and stone piles also provide nesting pollinator habitat should be burned, mowed habitat for bumble bees. or hayed at any one time in order to protect dormant pollinators, foraging adults and For wood-nesting bees, allow snags and dead other wildlife. Th is will allow for re-colo- trees to stand as long as they do not pose a nization of the disturbed area from nearby risk to property or people. undisturbed refugia (Hartley et. al., 2007). In order to maximize foraging and nest- ing opportunities, maintenance activities should be avoided while plants are in flower (Smallidge and Leopold, 1997). Ideally, mowing or haying should be done only in the fall or winter. Grazing can be a valuable tool. However, grazing is usually only beneficial at low to moderate levels and when the site is grazed for a short period followed by ample recov- ery time – and when it has been planned to suit the local site conditions. Areas of brushy vegetation will offer nest sites for Protecting bee nests bumble bees. Photo by Mace Vaughan, The Xerces Society. Native bees often nest in inconspicuous loca- tions. It is important to retain as many natu- rally occurring sites as possible and to create Providing alternative forage new ones where appropriate. Undeveloped areas on and close to farms can Ground-nesting bees seldom nest in rich serve as long-term refuge for native wild pol- soils, so poor quality sand or loamy sand linators. Protecting, enhancing or provid- soils may provide fine sites. In order to protect ing habitat is the best way to conserve nativePage 8 ATTRA Alternative Pollinators: Native Bees
  9. 9. are not available. Mixtures of native and non-native plants are also possible, as long as non-native species are not invasive. Distance from fields The typical foraging distance of native bees ranges from about 200 yards to a half-mile, with larger species able to fly farther. To be of greatest benefit to crop production, areas of natural habitat should be within a half- mile of an insect-pollinated crop. Ideally, potential nesting sites would be even closer (a couple of hundred yards), in order toThe USDA-NRCS and other agencies have advisors increase the number of small bees reaching awho can help. Photo by USDA-ARS. crop in bloom. T o be ofpollinators and, at the same time, provide Size of habitat greatestpollen and nectar resources that support Studies in California demonstrate that benefit tolocal honey bees. On farms with sufficient around 30 percent of the land within three-natural habitat, native pollinators can pro- crop production, quarters of a mile of a field should be in nat-vide all of the pollination for some crops. ural habitat in order to provide full pollina- areas of naturalSuch habitat can take the form of designated tion for watermelon (Kremen et. al., 2004). habitat should bepollinator meadows (bee pastures), orchard Similarly, studies in Canada have shown within a half-mileunderstory plantings, hedgerows and wind- that in the absence of honey bees canola of an insect-breaks with flowering trees and shrubs, farmers can increase their income because pollinated crop.riparian and rangeland revegetation efforts, of increased pollination by native bees if 30flowering cover crops and green manures, percent of their farmland is left in naturaland other similar efforts. habitat (Morandin and Winston, 2006). In a mixed landscape straddling the New Jer-Where possible, locally native plants are sey-Pennsylvania border, crops of tomatoes,often preferred for their ease of establish- peppers and watermelons all received highment, greater wildlife value and their co- visitation from native bees because of theevolution with native pollinators (Kearns et. presence of woodlands (up to 60 percent ofal., 1998). Non-native plants may be suitable the land within 1.25 miles of a field) andon disturbed sites, for specialty uses such other habitat areas between fields (Winfreeas cover cropping and where native plants et. al., 2008). Scientists and growers are still learning about how much habitat is needed for other crops. In general, a sound strategy is to make hab- itat patches as large as feasible within the constraints of a farm and to create as many patches as possible. Larger areas of habi- tat ensure a greater likelihood that forage, nest sites and nest building materials will be available within the bees’ flight range and throughout the flight season. Habitat corridorsField edge hedgerow, with natural area is background;nearby habitat supports pollinator populations. Cultivated fields have replaced most of thePhoto by Mace Vaughan, The Xerces Society. natural habitat in many modern ATTRA Page 9
  10. 10. If a farm already grows a diversity of crops, the timing of flowers produced by non-crop plants is less of a concern and the crops them- selves help provide a sequence of bloom. For example, vegetable farmers might allow some salad, root and herb crops to bolt. In addition to pollinators, the predators and para- sitoids of many pests are attracted to the flow- ers of plants like dill, cilantro, arugula, chervil, chicory, mustards, carrots and radishes. Finally, avoid plants that serve as alternate pest and disease hosts and plants that are likely to become weeds in the primary crop.Hedgerow and woodlots close to fields (within flight range) support native pollinator Technical andpopulations. Photo by Scott Bauer, USDA-ARS. f inancial assistance landscapes, resulting in significant distances Technical support and financial incentive between areas of habitat that harbor native programs are available to landowners who pollinators. Continuous, permanent strips are interested in setting aside, enhancing or of vegetation can link these patches and restoring some of their land for pollinator potentially increase the rate at which polli- habitat in the United States. nators and other wildlife colonize new areas Several USDA programs administered of habitat near agricultural fields. They also through the Natural Resources Conserva- may serve to grab the attention of bees fly- tion Service (NRCS) provide planning assis- ing across the landscape. These long narrow tance and financial support for the creation habitat features can aesthetically enhance drainage ditches, fencerows and roadsides. of new wildlife habitat, and in some cases Increased connectivity, particularly between actual rental payments to growers. Among larger areas of natural habitat, will bring a the most well known of these programs is greater overall benefit. the Conservation Reserve Program (CRP), which pays landowners for the conversion of marginal cropland to a less intensive use Select plants that (Vaughan and Skinner, 2009). complement the crop Most bees emerge before crops come into Historically these programs were intended bloom and many to reduce erosion, protect water quality and bee species are still provide habitat for wildlife such as pheasants active after ward and whitetail deer. Language in the 2008 the crop bloom Farm Bill, however, has made the promotion period. Therefore, and conservation of pollinator habitat a pri- plenty of forage ority among USDA conservation programs. should be available before and after In many states, three programs, the Wildlife a particular crop Habitat Incentives Program (WHIP), the comes into bloom. Environmental Quality Incentives Program This timing will (EQIP) and the Conservation Stewardship attract bees and Program (CSP), offer specific technical and ensure that they fi nancial support for pollinator conserva-Insectary plants used within field as crop row-endmarkers. Photo by Matthew Shepherd, The Xerces can successfully tion (usually native wildflower plantings) onSociety. raise many young. farms (Vaughan and Skinner, 2009).Page 10 ATTRA Alternative Pollinators: Native Bees
  11. 11. In many cases, these programs can also be bare ground. You can create conditionsused for multiple purposes. For example, suitable to a variety of species by maximiz-plants attractive to pollinators could be used ing areas of untilled ground and preparingin a grassed waterway with the primary objec- designated areas of bare soil.tive of stabilizing a hillside against erosion. Soil piles might be constructed with soilFor information about these conserva- excavated from drainage ditches or silt traps.tion programs, contact your nearest USDA Different species of bees prefer different soilNRCS office. Locations can be found at conditions, although research shows many bees prefer sandy or sandy loam soils. For a more formal look, make raised sandCreating artificial nest sites beds edged with lumber or bricks. Alterna-There are a number of ways to provide nest- tively, you can create a sandpit by simplying sites for different kinds of native bees, digging a pit 2 or 3 feet deep, and fill it withfrom drilled wooden blocks to bundles fine-grained, pale-colored sand or a sand-of reeds to sand pits or adobe bricks loam mixture (Vaughan and Black, 2006).(Shepherd et. al., 2003 and Vaughan and T These nesting areas can be as small as 1 o beBlack, 2006). Generally, increasing nesting to 2 square feet, but preferably should be sustainable,opportunities will increase bee numbers. several yards on each side. Your site can be artificialHowever, to be sustainable, artificial nests level or sloping, but it should be well-drained,need to be maintained over time to prevent nests need to be open and sunny. Place a few rocks in thethe buildup of parasites and disease (Bosch cleared area; they will retain heat and bees maintained overand Kemp, 2001 and Mader et. al., 2010). will bask on them (Shepherd et. al., 2003). time to prevent the buildup of parasites Colonization of these nest sites will depend on which bees are already present in the and disease. area, their successful reproduction and pop- ulation growth and the suitability of other nearby sites. Maintenance of nests for ground-nesting bees In general, ground-nest sites should receive direct sunlight and dense vegetation should be removed regularly by mowing, hand weeding or spot treating with herbicide, to make sure that some patches of bare ground are accessible. Once constructed, try not to walk or drive across the site. Remember that buried under the ground are possibly hundreds of bees.Drilled wood blocks offer nesting opportunities formany native bees. Photo by Katharina Ullmann, Nests for wood-nesting beesThe Xerces Society. Commercially produced bee blocks, consist- ing of a wood block drilled with a series ofNesting sites for dead-end holes, are now widely available.ground-nesting bees These types of bee nests were initially devel-The precise conditions needed by most oped in the 1960s by alfalfa seed producersground-nesting bees are not well known. in the western United States to attract andSome species nest in the ground at the base manage large numbers of the non-nativeof plants, and others prefer smooth, packed alfalfa leafcutter bee (Megachile rotundata) ATTRA Page 11
  12. 12. 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 popula- Nests made from stacks tions in unnaturally large numbers in a small of grooved boards can be opened easily space, they can become infested with para- to clean the tunnels. sites and disease spores after several seasons. Photo by Eric Mader, The Xerces Society. Without regular sanitation or the phasing out of nest materials, these parasites and dis- eases threaten long-term pollinator health wherever they are used. Because contami- nated nest blocks left unattended in the landscape continue to attract wild bees from the surrounding area, they have the potential to do harm (Mader et. al., 2010). Only with Bold markings help proper management can these nests main- bees find their nest tain healthy bee populations indefinitely. tunnels. Photo by Eric Mader, The Xerces Society. Wooden blocks Use preservative-free dimensional lumber to construct wooden nest blocks. A four-by-four is appropriate for blocks with smaller diame- ter holes. A four-by-six works for blocks with larger diameter holes. In one side, drill a series of nest holes of appropriate sizes and depths. Nesting holes should be between 3⁄32 and 3⁄8 inch in Occupied nest block showing nest seals of diameter. Holes of 1⁄4 inch or less in diame- neatly cut leaf pieces. ter should be 3 to 5 inches deep. Holes larger Photo by Eric Mader, than 1⁄4 inch should be 5 to 6 inches deep The Xerces Society. (Bosch and Kemp, 2001 and Shepherd et. al., 2003). The female bee controls the gen- der of her offspring and usually finishes the nest with a few male brood cells. A deeper hole ensures space for more female brood. 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 vege- tables. 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 Blue orchard bee nests in cherry orchard. Photo by year (Mader et. al., 2010). G. Neuenswonder, USDA-ARS.Page 12 ATTRA Alternative Pollinators: Native Bees
  13. 13. The holes should be about 3⁄4 inch from cen- Since these types of nests mimic trees fre-ter to center and no closer than that to the quented by woodpeckers, do not be surprisededges of the block. Attach a backing board if one finds your nest. To protect againstif you drill all the way through your block, damage, you might want to store your nestsbecause bees will not use a drilled hole that in an unheated building at the end of theis open at both ends. With smaller diame- season. Alternatively, you can protect nestster drill bits, you may not be able to achieve over the winter by surrounding them withthe 3-inch minimum recommended depth. hardware cloth. Be sure to remove the clothIf that is the case, simply drill as deep as you before nesting resumes because hardwarecan; bees that use holes of smaller diame- cloth can disorient nesting bees and damageters will often nest successfully in ones that their wings (Mader et. al., 2010).aren’t as deep.Bees may avoid a rough interior, so your Stem bundlesholes should be perpendicular to the wood’s In addition to wooden blocks, artificial nestsgrain and drilled with a sharp bit. You can can be constructed with bundles of reed, tea-buy paper straws to line the holes, although it sel, cup plant or bamboo cut so that a natu-may be hard to find straws that fit all diame- ral node forms the inner wall of the tunnel.ters. One solution is to wrap your own paperstraws out of parchment or newspaper usingdowels of various diameters that match theinside diameters of your drilled holes. Paintthe outer tips of the straws black to helpattract bees (Bosch and Kemp, 2001).The exterior of the block can be any color, Bamboo nest unitsalthough there is some anecdotal evidence in orchard. Photo bythat bees are most attracted to dark blocks, Eric Mader, The Xerces Society.which can be achieved by lightly charringthe front surface with a propane torch.Whatever the color, bees are likely to use theblock as long as the holes are of appropri-ate diameters and depths, and hung in anappropriate location. As a final step, you canattach an overhanging roof to provide addi-tional shelter from the rain.Colonization is often more successful whenblocks are attached to a large visible landmarksuch as a building. The actual height fromthe ground does not much matter, althoughif the nest is too low (less than a few feet),rain splash may dampen it and vegetationmay cover it. Nest blocks should be hung in aprotected location where they receive strongindirect sunlight. Direct sunshine in themorning will help bees warm themselves upto flight temperature, so you may wish to A plastic bucket makes a convenientplace nests facing east, allowing the morning container for bamboo or reed stems.sun to fall on the entrance holes. Direct sun- Photo by Eric Mader, The Xerces Society.light later in the day can be detrimental, caus- Blue orchard bee closing nest ining eggs or developing brood to overheat and bamboo tube. Photo by Mace Vaughan,die (Shepherd et. al., 2003). The Xerces ATTRA Page 13
  14. 14. Cut each stem below the nodes (usually Nesting materials indicated by a ridge) to create a handful of In addition to nesting holes, different spe- tubes, each with one open end. Strap the tubes together into a tight bundle with wire, cies need different materials to build their string or tape, making certain that the closed brood cells, which consist of intricate walls ends of the stems are all at the same end of that partition off the tunnel into a series the bundle. A variation on this is to tightly of separate chambers. These partitions seal pack the stems – open ends out – into a tin the nest entrances and protect the brood can, paper milk carton, square plastic buck- from predators. ets or short section of PVC pipe. The bun- Depending on the species, these walls may dles should be placed in a sheltered location be constructed of mud, plant resins, pieces of (such as the side of a barn or garden shed) with the stems horizontal to the ground. leaf, flower petals, fine pebbles and even cel- lophane-like glandular secretions (O’Toole and Raw, 1999). It is likely that these mate- Adobe blocks rials are already present in your area, but if Some solitary bees nest in cracks or cavi- you provide a diversity of native plants andC halkbrood ties in soft sandstone and dry exposed soil some mud puddles, you can guarantee it. spores embankments. Some of these species, such as Anthophora abrupta and Anthophora urbana, Keep in mind that bees may not fill the germinate will excavate tunnels in cliff sides by wetting entire length of a tunnel with cells, or theyinside the gut of the the hard soil surface with water or nectar to may die before an entire length of a cavity isdeveloping larva, soften it. These two species are important filled. For these reasons it can be difficult toproducing hyphae visitors of some fruit and vegetable crops and tell if a nest tunnel is occupied by just look-that eventually are quite common in the southeastern and ing for sealed entrances. southwestern United States, respectively.penetrate thegut wall, killing To attract these species, adobe bricks can Maintenance of tunnel-nests serve as the equivalent of a wooden nest Whether your nests are wooden blocks, twigthe larva. block. Such bricks can sometimes be pur- bundles or other materials, nests will need chased, in which case you can increase their attractiveness to bees by drilling nesting routine management in order to be sustain- holes following the size recommendations able. Nests also need regular replacement to listed above for wood blocks. prevent the build-up of parasites and diseases that affect the developing brood. Adobe blocks can also be easily made where clay soils are common. To create one, half-fill The hardest of these to control is chalkbrood a large bucket with clay soil, and then fill the (Ascosphaera spp.), a fungal disease. Several bucket with water. Stir the mixture together species of the fungi exist among tunnel-nest- to create a muddy slurry and allow it to set- ing bees, all of which are different from the tle. Remove any sticks or debris floating on chalkbrood disease that attacks honey bees. the surface and slowly pour off most of the Bee larvae become infested with disease water. Finally, pour the remaining sediment spores through contaminated pollen, either into a mold (such as a wooden box or small collected from a flower by the mother bee Styrofoam cooler), and allow it to dry for or accidentally spread when the mother bee several days or weeks. Before it completely emerges from a contaminated nest cavity dries, you can make several 1-inch indenta- (Mader et. al., 2010). tions, using the diameter guidelines above, to make it more attractive to bees. Mount the brick, either singularly or in a stack. Adobe will not hold up well in wet climates and many need sheltering from rain. You might want to supply a shallow water source near your bricks to help bees Inside of bamboo stem showing clean, healthy excavate their nests. cocoons. Photo by Eric Mader, The Xerces Society.Page 14 ATTRA Alternative Pollinators: Native Bees
  15. 15. provisioned cell, mite numbers can quickly climb into the thousands. While pollen mites usually cannot break through cell par- titions, they can persist for many months without food, until a bee deeper within theInside of bamboo stem showing nest infected with nest emerges from the tunnel and breaks thechalkbrood. Photo by Eric Mader, The Xerces Society. partition walls, allowing them to escape. It is not uncommon to see bees emerging fromAfter they are ingested, the chalkbrood infested nest blocks covered with so manyspores germinate inside the gut of the migratory mite nymphs that they havedeveloping larva, producing long filaments difficulty flying (Mader et. al., 2010).(hyphae) that eventually penetrate the gut To reduce these parasite and disease problems,wall, killing the larva. As the filaments con- we recommend one of three approaches:tinue to grow below the skin of the deceasedlarva, they eventually produce dark-colored 1. The holes of wood nest blocks can be linedspores. The appearance of infested cadav- with tight-fitting removable paper straws. Pers thus varies from white to grey to black At the end of the nesting season (autumn), ollen mitesdepending on the stage of fungal develop- the straws are gently removed, placed in feed onment. These brittle cadavers pose a hazard a ventilated container and stored either the pollento bees deeper within the nest block that, in a refrigerator or an unheated barn or provision, causingupon emergence, must climb over or chew garage. The nest block is then disinfected by submerging it in a bleach-water solu- the developing beethrough the spore-infested cell to escape thenest. Bees that emerge under these circum- tion (1:2 ratio) for a few minutes. In the larva to starve.stances have a high likelihood of spreading spring, fi ll the block with clean, previ-the spores to their own offspring. Similarly, ously unused paper straws and return it tobees searching for new unoccupied nest tun- its location. The old straws (with bees innels in which to lay their eggs frequently them) are placed alongside the nest block,investigate, and often select, previously used and the bees are allowed to emerge natu-tunnels. Over time, chalkbrood spores are rally. When the old straws are empty, theyspread throughout a nest block in this way are disposed of.(Mader et. al., 2010). 2. Wood and adobe nest blocks and stemAlong with chalkbrood, pollen mites in the bundles can be phased out every two yearsgenus Chaetodactylus can be a persistent by placing the blocks and bundles insideproblem in nest blocks that are in continu- a dark container, such as a light-proofous use for several seasons. Unlike the mites wooden box or even a sealed milk cartonthat attack honey bees, pollen mites do not that has been spray painted black to reducefeed on the hemolymph (blood) of the bee. light infiltration. A single 3/8-inch exitInstead, pollen mites feed on the pollen pro- hole is drilled in the bottom of the light-vision, causing the developing bee larva to proof container and the entire contrap-starve (Mader et. al., 2010). tion is hung adjacent to a new, previously unused nest block or stem bundle. As beesAdult pollen mites are usually white in color emerge from the old nest, they are attractedand measure about 500 microns in width, to the light of the exit hole and emerge toabout the size of the period at the end of this find the new one hanging nearby. The oldsentence. As with chalkbrood, adult bees nest block or stem bundle is then disposedmay accidentally pick up mites at flowers of at the end of the season.while foraging, or from climbing throughor investigating contaminated nest cavities. 3. The last alternative is to create multi-Migratory nymph stages of the mites cling ple small nest blocks or stem bundlesto a bee’s hairs and are transported back with only a few nest tunnels (4 to 6)to the nest, where they feed on the pollen and hang them at intervals of 25 feet orprovision and reproduce rapidly. In a single more. This prevents the unnaturally ATTRA Page 15
  16. 16. populations of bees found at nest blocks legs). The box must be weathertight; if the with many holes and mimics natural con- nest gets damp, the larvae may become too ditions of limited, spatially separated nest cold and mold and fungus will grow. sites. These smaller nests also decompose Place the nest in a dry, undisturbed area more rapidly and can be allowed to simply deteriorate naturally, while new small nests that has some obvious landmarks (a fence are added to the landscape periodically. post, rock or building) to aid bee naviga- tion; these landmarks are important to bees returning from foraging. Nesting boxes that Nest boxes for bumble bees are at ground level or slightly buried (either Unlike solitary bees, which can be very par- with soil or straw) are the most attractive to ticular about tunnel diameters, bumble bees queens of many species. Boxes placed on the are flexible in their nesting needs. All they surface should be level and stable. If you are want is a warm, dry cavity, roughly the size burying your box, extend the entrance pipe of a shoebox (Shepherd et. al., 2003). Artifi- so it gently slopes up to the surface and clear cial nests can be constructed to attract bum- the vegetation from an area a few inches ble bees, but occupancy is typically extremely around where the pipe surfaces. low – often far less than 25 percent. The best time to install a bumble bee nest A simple wooden bumble bee box can be box is in early spring, when the first queens made from preservative-free lumber. An have emerged from hibernation and are appropriate size will have internal dimen- searching for a nest site; in many areas, this sions of about 7 inches high by 7 inches is when the willows first start blooming. wide and 7 inches long. Drill a few ventila- tion holes on the upper sides of the box (near the roof) and cover with window screen to Maintenance of deter ants. Also drill some drainage holes in bumble bee nests the bottom. Make an entrance tunnel from Bumble bee nests require little maintenance. 3⁄4-inch diameter plastic pipe and fi ll the Watch your boxes through the spring and box with soft bedding material, such as short early summer. Any above-ground boxes that lengths of soft unraveled string, dry straw or are unoccupied by late July can be removed, upholsterer’s cotton (do not use cotton balls, cleaned and put into storage until the fol- as the fibers become tangled in the bees’ lowing spring. This is not vital, and if you have a lot of boxes on a large site it may not be practical. In late fall or early winter inspect all the boxes that have been occu- pied. Remove the old nests, clean them and make any repairs. Cleaning the boxes with a bleach-water solution (1:2 ratio) will help reduce parasites and diseases in the nests. The following spring, add fresh nesting material to all the boxes. Commercial native bee production Recently, many people have become inter- ested in the blue orchard bee (Osmia lig- naria), also called the orchard mason bee, as a garden and orchard pollinator. Many thousands of mason bee nesting blocks areBumble bee nest box showing construction. Photo by Matthew Shepherd, The sold each year in the United States, alongXerces Society. with hundreds of thousands of blue orchardPage 16 ATTRA Alternative Pollinators: Native Bees
  17. 17. bees. This interest has greatly raised public of one or more diseases which have decimatedawareness about the importance of pollina- several bumble bee species, even causing thetors; however, it is important to remember potential extinction of one species, Bombusthat raising large numbers of a single spe- franklini (Franklin’s bumble bee) (Evans et.cies (bee-ranching) is a different objective al., 2008).than the conservation of diverse species of There is an enormous need for managedwild pollinators. agricultural pollinators in this country, butAs mason beekeeping has increased in popu- it critical not to import non-local bees, espe-larity, important questions are being asked cially near wild areas, even if the bees areabout the risks associated with the nation- represented as being the same species as localwide shipment of blue orchard bees by com- bees. The alternatives are to either developmercial producers. In fact, there are two local commercial sources of bees that aredistinct subspecies of the blue orchard bee: native to your region or to rear alreadyOsmia lignaria propinqua in western North widely established non-native species, suchAmerica and Osmia lignaria lignaria in the as honey bees or the alfalfa leafcutter bee, aseast. The species is rare in the Great Plains managed pollinators.region, although some intermediate speci-mens have been collected. Common native beesMost commercial producers of the blue orchard Globally, bees are grouped into seven fam-bee are located in the Pacific Northwest, where ilies. Six of these have species in Norththey rear the locally native western subspe- America, although only five, the Colleti-cies (Mader et. al., 2010). Unfortunately, the dae, Andrenidae, Halic-bees these producers raise are then marketed tidae, Megachilidae andnationwide, resulting in the frequent shipment Apidae, are commonlyof locally non-native bees to the eastern United encountered. The familyStates. The potential ecological consequences Melittidae is representedof the western blue orchard bee hybridizing only by about 60 gener-with its eastern subspecies are unknown. Simi- ally uncommon species inlarly, these shipments have the potential to North America (Michener,introduce locally non-native parasites and 2000 and O’Toole and Raw, 1999).diseases. For the consumer, there is anothersignificant drawback. The western bees maynot develop in sync with local conditions, Colletidae:resulting in poor establishment and poor Polyester beesperformance as pollinators. The net result Bees in the family Collet-is that people purchasing blue orchard bees idae are highly varied inover the Internet or through garden catalogs appearance and have fewmay be doing more to harm their local pol- Metallic green sweat bee. Photo by Susan Ellis, common features. One fea- populations than to help them – and ture consistent to all col-not be getting the pollination they paid for. letid bees is that their tongue has a branchedSimilarly, the package bumble bee industry, tip. Colletids secrete a plastic-like substancewhich provides farmers with live bumble bee (hence the family’s common name) that theycolonies for crop pollination, currently only use to waterproof their brood cells. This allowsproduces a single eastern bumble bee spe- the bees to nest in periodically flooded areascies, Bombus impatiens. This species is then such as stream banks. The two genera mostshipped nationwide, in a situation similar frequently seen are Colletes and the blue orchard bee, often far beyond itsnative range. Many bumble bee scientists now Andrenidae: Mining beesbelieve that these commercially produced With just over 1,400 hundred species inbumble bees are responsible for the introduction North America, Andrenidae is the ATTRA Page 17
  18. 18. diverse family of bees on the continent. Andrenidae are abundant in the spring and, as their common name indicates, excavate nests in the ground. The huge majority of species in this family are solitary. A small number of species are communal, with sev- eral females sharing a nest entrance but each excavating and provisioning their own brood cells. They generally nest in flat or gently sloping sites and may form aggregations with tens of thousands of bees nesting in a small area. Commonly encountered genera Leafcutter bee foraging on pea flower. Photo by are Andrena and Perdita. Whitney Cranshaw, Colorado State University. Courtesy of Halictidae: sweat bees Halictidae are among the most frequently encoun- tered bees during sum- mer. Although this fam- ily includes brightly colored metallic bees, the majority of halictids are drably colored and small. Most Halictidae exca- vate nests in the ground, though some nest in rot- Leafcutter bee resting on leaf. Photo by Joseph Berger, ting wood. The genus Lasioglossum includes the whole gamut of social into which they pack dry pollen for trans-Sweat bee foraging in California poppy. Photoby Matthew Shepherd, The Xerces Society. behaviors from solitary port back to the nest. The great majority of to semi-social (nests con- megachild bees nest in existing cavities above structed by a group of ground (beetle tunnels in snags, crevices in bees in which one is the rocks) and collect items such as leaf pieces egg-laying queen). The or wet soil to divide the nesting tunnel into bright green Agapostemon brood cells. This family includes the com- is communal; a dozen or monly managed leafcutter (Megachile) and more females may share a mason bees (Osmia). nest entrance, but under- ground each bee cre- ates her own brood cells. Apidae: Bumble, carpenter Other common genera in and other bees this family are Halictus, The Apidae is an immensely diverse familyMetallic green sweat bee. Photo by Susan Ellis, Augochlora, Nomia and that includes bumble bees (Bombus) as Augochlorella. as a wide range of less well-known yet fre- quently encountered groups such as the dig- Megachilidae: Leafcutter ger (Anthophora), squash (Peponapis) and and mason bees sunflower (Svastra) bees. Given the diversity Megachilidae is one of the easiest families to of its genera, it will come as no surprise that recognize because its members don’t carry pol- the Apidae displays the full range of nest- len on their legs. Instead, they have rows of ing behaviors from solitary to social and has stiff hairs on the underside of their abdomen species that nest in the ground, in wood andPage 18 ATTRA Alternative Pollinators: Native Bees