What’s the Buzz About Native Bees?

by Robin Finehout

Thanks to Linda and Tom Ligon, Nancy Berlin and Harriet Carter for pictures and advice!

The Teaching Garden has always been native bee friendly! Our gardens have many native plants and flowers intended to attract pollinators including wild bees, butterflies and hummingbirds. All of our plantings are designed with pollinators in mind. We are mindful of not using pesticides, use plants that naturally discourage pests, and make sure we have constant blooms designed to feed pollinators all season. You can find bee friendly block plantings of buckwheat and zinnias, edge plantings of hyssop and hairy vetch, and cover crops such as Crimson clover in our Cooks gardens.  Letting herbs in the Herb bed such as fennel, rosemary and thyme bolt and bloom is an excellent way to provide nectar and pollen. All of our beds use plants to attract  native bees, such as Coreopsis, Salvia, and lavender. You will also find a number of native bee nesting houses designed to attract mason and leaf cutter bees. These structures provide artificial nesting sites for solitary bees with tubes that can be used for cells for the eggs and larvae.

Native bees are important pollinators of wild flowering plants and agricultural crops. Bees, including domesticated honey bees, provide an essential ecosystem service by pollinating 80% of all flowering plants worldwide, but also pollinating over 1/3 of global agricultural crops. There are an estimated 35,000-40,000 species of bees worldwide, 3,500-4,000 species of native bees in North America, and 500 species identified in the Mid-Atlantic region. Bees can be found on every continent except Antarctica, and are believed to have co-evolved with flowering plants 125 million years ago. They are found in habitats with insect pollinated plants and their life cycles are timed with seasonal plant reproduction. The USDA reports that 75% of the fruits, nuts and vegetables are pollinated by native insects and honey bees, which adds $15 billion increased crop yield per year.

When most people think about pollination of agricultural crops, they think of the honey bee. The European honey bee (Apis melifera) was brought to North America by European colonists in the 17th century and quickly escaped and naturalized. The honey bee is now used to pollinate large scale monoculture plantings and is efficient because they move from plant to plants over a large area. Important to agriculture, they can be moved from field to field timed to flowering. However, in the 6 years leading up to 2013, it is estimated that 10 million honey bee hives were lost, often to Colony Collapse Disorder. Although the exact mechanism is still unknown, CCD is believed to be caused by a synergetic combination of stress factors such as pesticide use, viruses, genetic factors, Acarapsis and Varroa mites.  Research has shown that native bees are more efficient at pollination of many crops and less susceptible to CCD and serve as an alternative or enhancement to the honey bee.

Native bees are more efficient at pollinating North American forest and meadow plants such as hawthorn, serviceberry, mountain ash, but also Asian cousins such as apple, plum, cherry, pear and peach. They are considered to be two to three times better at pollination of squash, tomato, peppers, beans and peanuts, and studies have shown that pollination by wild bees enhances the yield and the quality of a variety of important economic crops. Providing uncultivated land, or habitat for wild bees near field edges has shown to increase crop yield and profit.  In Virginia, many crops are dependent on pollinators, including native bees.  These include alfalfa, apples, tomatoes, cotton, cucumbers, squash, watermelon, peanuts, snap beans and soybeans.  Other Virginia crops that benefit from native pollinators include blueberries, raspberries, blackberries and pitted fruit such as peaches and plums. The most important wild bee crop pollinators in Virginia are: Mason bees (orchard crops), digger bees (berries), squash bees, sweat bees (asters), leafcutter bees (legumes), and bumble bees (generally all flowering plants).

All bees feed on both nectar (for energy) and pollen (for protein and nutrients). The majority of pollen and nectar is stored as larvae food. Most bees build nests and provide food for their offspring, although some rely on other nests (cuckoo bees). They stock their nests with pollen and nectar before laying eggs. Most bees have very furry bodies, better for trapping pollen, or pollen baskets for collection of pollen. They have fairly long tongues to sip nectar and a large crop, or second stomach for carrying it.  Bees find flowers through smell, colors and patterns and a great memory. They can be eusocial displaying cooperative brood care in a colony, or solitary laying eggs in individual cells in a nest.

There are two types of foraging strategies found in bees: Generalist and specialist.  Specialist bees feed from only one species of plant, sometimes 2 and at most 3 species.  It is estimated that 20% of the wild bee population are specialist foragers, with some 100 species of native bees in the Mid-Atlantic region.  In this feeding strategy, bees emerge from their nests at the same time the host plant is flowering. In this mutualist relationship, the host plant is dependent on one specific bee species for fertilization. Examples include squash, dependent on the squash bee (Peponapis pruinosa) and the sunflower, dependent on the sunflower bee (Diadasia enavata). Specialist bees have a shorter feeding season, have lower population numbers and typically have only one brood per season. Other examples of specialist native bees found in the Mid-Atlantic are Andrenidae (mining bees) and Colletidae (plaster bees).

Generalist bees make up 80% of the total bee population and sustain themselves by foraging on  many different species. They visit a wide range of diverse species for nectar and pollen, have a higher population number and numerous and continuous broods. Examples of generalists include leafcutters and many bumble bee (Bombus) species. Honey bees are also generalists.

All bees, native and honey bee, are currently suffering from decreasing populations believed to be caused by a combination of factors. Colony Collapse Disorder (CCD) of honey bees has been attributed to a synergistic combination of stress factors such as wide spread use of pesticides, parasitic mites, viruses, habitat loss and fragmentation. Native bees have also seen population declines and range reductions. Widespread use of monoculture agricultural plantings and decrease use of native plants is also seen as contributing factors. It is important to consider the use of wild bees as an alternative, or to augment honey bees, to offset losses due to CCD.  Urban and agricultural areas and home owners can encourage native bee populations by planting native plants in the landscape or by intercropping and block planting native plants with vegetable and fruit crops. Landscape practices such as rototilling a spot for digging bees, providing bee nesting structures, providing a source of mud, and a pesticide-free water source are all ways to help promote health populations of wild bees.  Helping native bees is essential to the continued productivity of farms, forests, gardens and ecosystems.

 

Groups of Native Bees:

Carpenter Bees

Family: Apidae

 Example:  Xylocopa virginica  Eastern Carpenter Bee

 

Carpenter bees are large, solitary bees that resemble bumble bees, but the upper surface of their abdomen is bare and shiny black. Using powerful jaws to excavate tunnels in wood, they build their nests in the ends of logs and areas where bare wood is exposed. Both the male and the female cut ½” circular holes as an entrance to tunnels that run parallel to the surface. The female stores food made from pollen and nectar and then lays her eggs in individual cells. Carpenter bees have one generation per year. Carpenter bees dislike paint and wood finish, so it is important for homeowners to paint or stain all outside surfaces, including exposed areas on decks.

 

Bumble Bees

Family: Apidae

Example: Bombus spp., Bombus impatiens Common Eastern Bumble Bee

 

Bumble bees have stout, hairy and robust bodies, ¾ to 1 ½ “ long,  and are usually black, yellow and/or red striped. They are variable in size and color patterns even within the species. Patterns of stripe coloration on the abdomen and thorax are used for identification. Bumble bees are 2-3x’s the size of honey bees and are generalist feeders. They need to forage on a wide variety of plant species and in a wide range of weather conditions, to support a colony. Bumble bees are able to fly in cooler temperatures and lower light levels than many other bees, making them excellent pollinators for higher elevations and in early spring.  They are active in late winter (February), are last in the fall (November), and are pollinators of spring ephemerals such as Dutchmans Breeches (Dicentra cucullaria).  While foraging the female carries pollen in a concave, hairless area surrounded by stiff hairs on the rear legs called a “corbicula”. Bumble bees are known for using a behavior known as “buzz pollination” where they grab the flower in their jaws and vibrate the wing muscles to dislodge the pollen. Buzz pollination is highly efficient in cross pollinating crops such as tomato, pepper and blueberry. Tomato does not require this type of pollination, however bumble bees may produce bigger and better-shaped fruits when they contribute to their reproduction.

Bumble Bees of Virginia (1)

Like honey bees, most species of bumble bees are eusocial and display cooperative brood care. They nest in a variety of places, often choosing nest sites around houses and wood storage sheds. Most bumble bees nest in the ground during the summer, and queens overwinter an inch or two below the soil surface. They have long lived colonies which start in spring and last until fall. When not working, females rest inside the nests. Males have nothing to do with nest building and can be found resting in other locations. Newly mated queens hibernate and do not need vast amounts of honey, but do however, make a small amount of honey to feed the colony during bad weather. Bumble bees produce smaller annual colonies then honey bees, numbering around 50-1500 individuals.  Due to smaller annual population sizes, bumble bees are susceptible to extinction. Twenty eight percent of all North American bumble bees are facing some risk of extinction due to the combined effects of habitat loss and fragmentation, disease, parasites, pesticide use and climate change. The Rusty Patched bumble bee (Bombus affinis) population is steeply declining and is estimated to have declined by 80%. It is now found only in isolated areas.

 

Andrenid Bees (miner or digging bees)

Family: Andrenidae

Examples: Colletes inaequalis Plaster bee, Andrena nubecula mining bee

Andrenid bees are a large sized family of about 750 species,that are important pollinators of crops and fruit trees.  They are about the size of a honey bee but darker, and can be brightly striped. Some are nondescript and black, although others can be bright red or metallic, with wings that appear short for their body type. They are all ground nesters and are one of the first species to emerge in the spring. Miner bees are solitary, but females nest in the ground in large numbers when soil is favorable.  They are only out a few weeks per year (2-4 weeks) when individual females make nests for developing larvae. Andrenid bees rarely sting, are non-aggressive unless handled, but will fly up as a group as a defense mechanism. They spend most of the season as immature bees. Miner bee nests can be identified by ¼” holes found in exposed and well-drained soil, often surrounded by a small mound of soil. They should be left alone, but can be controlled through elimination of bare patches of soil either with mulch or ground covers. In lawns, keep bare patches to a minimum. Ground nesting bees prefer soils with moderate level of disturbance, bare ground to sparsely vegetated areas, and clumping native grasses and can be encouraged to nest in these areas.

 

Leafcutter Bees

Family: Megachilidae

Examples: Megachile spp, Dianthidium spp.

Leafcutters are valuable and efficient pollinators found in the Megachile family. According to the USDA, one alfalfa leafcutter can pollinate as many plants as 20 honey bees.  They are also highly efficient pollinators in greenhouses.  Leafcutter bees are small and solitary, and are considered to be cavity nesters. Nesting in ready-made cavities or soft rotting wood, they cut out small pieces of leaf in perfect circles to fill a nesting area for immature bees. Here, they build cells sealing them with a little piece of leaf, or even petals.  Adults are important and beneficial pollinators of crops and native plants. Leafcutters look similar to honey bees, but are darker in color. Adults do not have pollen baskets on their hind legs, but collect pollen on hairs on their underside of the abdomen.  Non-aggressive unless handled, they also make excellent garden pollinators. Home gardeners can encourage nesting behavior by building bee houses.

 

Orchard/Mason Bees

Family: Megachilidae

Examples: Osmia spp

Mason bees, also known as orchard bees, are frequently metallic blue or green, many are blackish and one species is rust red. All mason bees are solitary and do not produce honey or beeswax.   Mason bees make excellent pollinators and are very productive in pollinating spring flowers and fruit and nut orchards. They are solitary bees that use mud as a masonry product to seal off the entrance hole when making nests in dark cavities such as hollow stems or holes made by other insects. There are 300 species found in North America, and are cultivated in different parts of the world to improve pollination of orchard fruit and nuts, as an alternative to honey bees.  An individual mason bee can visit up to 60,000 flowers in its lifetime, and like the bumble bee, will forage in colder temperatures and earlier in the spring.  Females carry pollen from plant to plant on the underside of their hairy abdomen, and it is carried dry and scraped off in the nesting hole. Each egg is sealed in a chamber and sealed with mud. Mason bees need a supply of mud nearby, and will search for areas where it can be found.  They are gentle enough to touch, rarely sting and their stinger is unbarbed. Homeowners and farmers will find that mason bees are easily raised by providing nesting houses. These are affordable to buy already constructed or can be made at home with affordable materials.

 

Sweat Bees

Family:  Halictidae

Examples: Agapostem viriscens

Lasioglossum spp.

Sweat bees are beneficial bees that occur worldwide, are usually dark colored and often bright metallic color. They are attracted to the salt in perspiration and can be a nuisance to anyone working or entertaining outdoors in the heat of summer. Most are ground nesters, and a few species will nest in wood. Females make vertical chambers with side passages that lead to nesting chambers. In these chambers they leave the egg with a mass of pollen and nectar with the egg laid on top. Some species of sweat bees are considered “eusocial” and exhibit cooperative brood care with a queen and defined caste system. Some species of sweat bees are nocturnal, active only at dusk or early evening. Repellents can be used to discourage visits from sweat bees during outside activities. They will sting if disturbed, but the sting is considered minor.

 

Cuckoo Bees

Families: Apidae, Halictidae, Megachilidae

Examples: Spheodes spp, Coelioxys spp. (Cuckoo Leafcutter)

Cuckoo bees only lay eggs in the constructed nests of a few bee species and practice kleptoparasitic behavior. They enter the nest of a pollen collecting species to lay eggs in the cell made by the host bee.  The Cuckoo bee larvae consumes the host larvae’s food (pollen ball) and may kill and eat the host larva.  Some species of parasitic bumble bees can infiltrate nests of nonparasitic bumble bees, lay eggs, and kill and replace the queen. Often, the kleptoparasitic bee is similar in appearance to the host.  Females lack pollen collecting structures, have reduced body hair, and do not construct their own nets.

 

References:

https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5306468.pdf

http://xerces.org/bumblebees/

http://www.xerces.org/wp-content/uploads/2008/10/agroforestrynotes32-overview.pdf

https://xerces.org/pollinator-conservation-roadsides/

https://xerces.org/guidance-to-protect-habitat-from-pesticide-contamination/

http://www.xerces.org/wp-content/uploads/2008/10/factsheet_value_of_native_bees_for_agriculture.pdf

http://www.xerces.org/wp-content/uploads/2016/10/2017-049_Mid-AtlanticPlantList_Dec2017_web-3page.pdf

https://growingsmallfarms.ces.ncsu.edu/growingsmallfarms-pollinatorconservation/

https://www.fs.fed.us/wildflowers/pollinators/documents/BumbleBeeGuideEast2011.pdf

http://www.xerces.org/wp-content/uploads/2008/06/2012_AGEE_lr_sec.pdf

http://articles.extension.org/pages/19581/conserving-pollinators:-a-primer-for-gardeners

http://www.xerces.org/wp-content/uploads/2013/06/NeonicsInYourGarden.pdf

 

Great photos that can be used; public domain

https://www.flickr.com/photos/usgsbiml/

Teaching garden photos by MG photographer www.justKim.com 

 

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