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Megachile rotundataalfalfa leafcutting bee

By Alexis Yajcaji

Geographic Range

Alfalfa leafcutting bees, Megachile rotundata, are native to southwestern Asia and southeastern Europe. There were introduced to North American in the 1930's and more recently to Australia to increase pollination of Alfalfa crops. (Kemp and Bosch, 2000; Peterson, et al., 1992)

Habitat

Alfalfa leafcutting bees nest in a variety of locations such as rotting wood, flower stems, soda straws, and other spaces that allow for the construction of tubular nests. They also adapt well to man-made structures.

After selecting and preparing a nest site, alfalfa leafcutting bees seek out leaves to make individual nesting cells within the nest. They often use leaves of Virginia creeper (Parthenocissus quinquefolia) and green ash (Fraxinus pennsylvanica). Alfalfa leafcutting bees cut distinct circles about 2.5 cm in diameter in these leaves, which are used to create nest cells. Nests may contain up to 2 dozen cells and measure 18 cm in length. ("Use of the Alfalfa Leafcutting Bee Growing in California", 1995; Brewer, 1995; "Common Missouri Wasps and Bee Species", 2000; Cranshaw, 2006; "Alfalfa Leafcutting Bees", 2003)

Physical Description

Alfalfa leafcutting bees are the smallest leafcutting bees, ranging in size from 60 to 190 mm. They are dark gray in color and demonstrate sexual dimorphism. Females have a white scopa, elongated hairs for carrying pollen, on the underside of the abdomen, and shorter white hairs on the rest of their body. Males tend to have a pair of creamy white to yellow spots near the end of the abdomen (Brewer, 1995; "Common Missouri Wasps and Bee Species", 2000; Tirlea, 2005)

  • Sexual Dimorphism
  • sexes colored or patterned differently
  • Range length
    60 to 190 mm
    2.36 to 7.48 in

Development

Alfalfa leafcutting bees undergo complete metamorphosis, and have 4 larval instars. After hatching from eggs in early winter, larvae grow and develop until spring. They overwinter as mature larvae. As temperatures reach 24 to 30 ˚C in the Spring, larvae develop into pupae over the following 3 to 5 weeks. As larvae and pupae, they feed on provisions which were wrapped inside the nest cell by their mother. After 18 to 20 days, adult males begin to chew their way out of the cell. Females exit the cell after 21 to 24 days. ("Alfalfa Leafcutting Bee Biology and Management", 2007; Kemp and Bosch, 2000; "Alfalfa Leafcutting Bees", 2003)

Reproduction

After adult female alfalfa leafcutting bees emerge from nest cells, they immediately start to mate. A male lands on a female and lifts her abdomen with his legs. If the female accepts the invitation, she withdraws her singer and unites her genitals with those of the male. Mating lasts between 30 and 45 seconds. Alfalfa leafcutting bees are polygynous. (Cranshaw, 2006; "Alfalfa Leafcutting Bees", 2003)

Female alfalfa leafcutting bees breed immediately after exiting the cell. Breeding occurs once a year, usually during June and July. Shortly after mating, female alfalfa leafcutting bees lay their eggs inside nest cells. Females lay between 18 and 40 eggs over a period of 2 weeks (average less than 25 eggs). Most eggs are fertilized, although unfertilized eggs are generally born as males. Some seasons yield fewer males than other seasons. ("Use of the Alfalfa Leafcutting Bee Growing in California", 1995; Cranshaw, 2006; "Alfalfa Leafcutting Bee Biology and Management", 2007; "Alfalfa Leafcutting Bees", 2003)

  • Breeding interval
    Alfalfa leafcutting bees breed once per year.
  • Breeding season
    Breeding of alfalfa leafcutting bees usually occurs between June and July.
  • Range eggs per season
    18 to 40
  • Average eggs per season
    <25
  • Range gestation period
    1 to 2 1/2 weeks
  • Average gestation period
    2 weeks

Female alfalfa leafcutting bees prepare a nest and nest cells for their offspring. They provide nest cells with nectar and pollen to provision offspring. Before laying her eggs, a female thoroughly cleans her abdomen with her legs to ensure eggs are clean. Eggs are laid in nest cells over a period of 2 weeks. After this time, females die, and offspring develop without further parental care. ("Use of the Alfalfa Leafcutting Bee Growing in California", 1995; Cranshaw, 2006; "Alfalfa Leafcutting Bee Biology and Management", 2007; "Alfalfa Leafcutting Bees", 2003)

  • Parental Investment
  • female parental care
  • pre-fertilization
    • provisioning
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • inherits maternal/paternal territory

Lifespan/Longevity

In captivity, female alfalfa leafcutting bees usually live 1 to 2 months, and males live 3 to 4 weeks. Lifespan is affected by weather, environmental conditions, and how well parasites are controlled. Lifespan is shorter in the wild due to uncontrolled environments; females generally live 3 to 5 weeks and males 1 to 3 weeks. ("Alfalfa Leafcutting Bee Biology and Management", 2007; "Alfalfa Leafcutting Bees", 2003)

  • Range lifespan
    Status: wild
    7 to 35 days
  • Range lifespan
    Status: captivity
    <1 to 2 months
  • Average lifespan
    Status: captivity
    1 months
  • Typical lifespan
    Status: wild
    7 to 28 days
  • Average lifespan
    Status: wild
    14 days
  • Typical lifespan
    Status: captivity
    1 to 2 months
  • Average lifespan
    Status: captivity
    1 months

Behavior

Unlike honeybees, which live in colonies, leafcutting bees are solitary. They do not have a queen or divide labor. Females independently create a nest and provision nest cells for their young. Although they are independent, alfalfa leafcutting bees prefer to live near others of their species. Because they are gregarious and can live in man-made shelters, they are often reared and managed by humans as crop pollinators. Females spend nights in their nest and are most active on warm sunny days when temperatures exceed 20˚C. They generally do not forage when it is considerably cloudy or below temperatures of 20˚C. Alfalfa leafcutting bees are inactive during colder months, overwintering as mature larvae. Adult female alfalfa leafcutting bees use their stinger to defend themselves, but they are not aggressive. Unlike honeybees, they do not leave their stinger behind when they sting, nor do the die after stinging. ("Use of the Alfalfa Leafcutting Bee Growing in California", 1995; Cranshaw, 2006; "Alfalfa Leafcutting Bees", 2003; Tirlea, 2005)

Home Range

Little information is available regarding the home range of alfalfa leafcutting bees. Nests are created by individual bees and, unlike honeybees, alfalfa leafcutting bees do not defend their homes. ("Use of the Alfalfa Leafcutting Bee Growing in California", 1995; "Common Missouri Wasps and Bee Species", 2000; Cranshaw, 2006)

Communication and Perception

Alfalfa leafcutting bees, like most bees, can perceive ultra-violet light as well as most colors visible to humans. They are able to return to nesting sites as well as favored foraging areas. When in captivity, they place their nests near knotholes, edges, or other markers. Little is know regarding communication between alfalfa leafcutting bees. ("Alfalfa Leafcutting Bees", 2003)

Food Habits

Leafcutting bees in the genus Megachile are typically polylectic, gathering food from many different plants. Alfalfa leafcutting bees, as their common name suggests, prefer alfalfa (Medicago sativa). Adults eat both nectar and pollen. Nectar is obtained by prying open the keel of plants and inserting their proboscis. Pollen is transported on the underside of the abdomen in pollen carrying brush, or scopa. Most other bees are unable to pry open the flower of alfalfa. ("Use of the Alfalfa Leafcutting Bee Growing in California", 1995; "Alfalfa Leafcutting Bees", 2003; Tirlea, 2005)

  • Plant Foods
  • nectar
  • pollen

Predation

28 species of organisms prey upon alfalfa leafcutting bees or destroy their nests. Their primary predators are checkered flower beetles, which invade nest cells and feed on larvae. (Peterson, et al., 1992)

  • Known Predators
    • checkered flower beetles Trichodes ornatus

Ecosystem Roles

Alfalfa leafcutting bees are important pollinators, especially of the plant alfalfa (Medicago sativa). They are preyed upon by 28 different species and act as host to 8 species of parasites. Parisitoids of the genera Pteromalus, Monodontomerus, Tetrastichus and Melittobia emerge before bees and parasitize bees as they develop. Alfalfa leafcutting bees are also vulnerable to a chalkbrood disease (Ascosphaera aggregate Skou), which is caused by a fungus. This fungus invades nest cells of developing larvae and infects them, causing larvae to harden, take on the consistency of chalk, and turn either white, black, or gray. Infected larvae die before reaching maturity. This disease is spreading rapidly and could ultimately affect crops of alfalfa as numbers of pollinators decrease. ("Common Missouri Wasps and Bee Species", 2000; "Alfalfa Leafcutting Bee Biology and Management", 2007; Peterson, et al., 1992)

  • Ecosystem Impact
  • pollinates
Commensal/Parasitic Species

Economic Importance for Humans: Positive

Because they are such effective pollinators of alfalfa (Medicago sativa), alfalfa leafcutter bees were introduced to North America in the 1930's to aid alfalfa crop production. Crop production is said to have increased by nearly 60% in some areas of North America. ("Use of the Alfalfa Leafcutting Bee Growing in California", 1995; "Common Missouri Wasps and Bee Species", 2000; Peterson, et al., 1992)

  • Positive Impacts
  • pollinates crops

Economic Importance for Humans: Negative

Although alfalfa leafcutting bees cause some leaf and flower damage to ornamental plants, the effect is minimal. They also sting humans when handled, though the sting is considered half as painful as that of a honeybee. ("Alfalfa Leafcutting Bee Biology and Management", 2007; "Alfalfa Leafcutting Bee Biology and Management", 2007)

  • Negative Impacts
  • injures humans
    • bites or stings
  • household pest

Conservation Status

Alfalfa leafcutting bees are not currently considered threatened. In California, however, a recently introduced species of bee, Megachile apicalis, may compete with alfalfa leafcutting bees for nesting material. (Peterson, et al., 1992)

Contributors

Alexis Yajcaji (author), Rutgers University, David V. Howe (editor), Rutgers University, Gail McCormick (editor), Animal Diversity Web Staff.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

arboreal

Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

cooperative breeder

helpers provide assistance in raising young that are not their own

diurnal
  1. active during the day, 2. lasting for one day.
ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

herbivore

An animal that eats mainly plants or parts of plants.

hibernation

the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.

internal fertilization

fertilization takes place within the female's body

introduced

referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nectarivore

an animal that mainly eats nectar from flowers

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

World Map

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

polygynous

having more than one female as a mate at one time

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

suburban

living in residential areas on the outskirts of large cities or towns.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

urban

living in cities and large towns, landscapes dominated by human structures and activity.

visual

uses sight to communicate

References

International Pollination Systems. 2007. "Alfalfa Leafcutting Bee Biology and Management" (On-line). Accessed November 11, 2007 at http://www.pollination.com/managed/alfalfabee.cfm.

Manitoba Forage Seed Association. 2003. "Alfalfa Leafcutting Bees" (On-line). Manitoba Forage Seed Association. Accessed November 11, 2007 at http://www.forageseed.net/index.php?option=com_content&view=article&id=131:leafcutting-bees&catid=38:sports&Itemid=136.

Conservation Commission of Missouri. 2000. "Common Missouri Wasps and Bee Species" (On-line). MDConline Missouri Department of Conservation. Accessed November 11, 2007 at http://mdc.mo.gov/discover-nature/avoid-outdoor-pests/common-missouri-wasps-and-bees.

BugInfo.com. 2007. "Leaf-cutting Bees" (On-line). BugInfo.com. Accessed November 09, 2007 at http://buginfo.com/article.cfm?id=103.

2007. "Report: Megachile Rotundata (Fabricius), Taxonomic Serial No: 154369" (On-line). Integrated Taxonomic Information System. Accessed November 11, 2007 at http://www.itis.gov/.

1995. Use of the Alfalfa Leafcutting Bee Growing in California. Seed Trade News, 116/9: 14. Accessed November 11, 2007 at http://www.pollination.com/publications/IPSpub01.cfm.

Brewer, M. 1995. Alfalfa Leafcutting Bee, Megachile Rotundata. University of Wyoming CES, B1013.5: 1-2. Accessed November 10, 2007 at http://www.wyomingextension.org/agpubs/pubs/B1013.05.pdf.

Cranshaw, W. 2006. "Leafcutter Bees" (On-line). Colorado State University Extension. Accessed November 11, 2007 at http://www.ext.colostate.edu/pubs/insect/05576.html.

Kemp, W., J. Bosch. 2000. Development and Emergence of the Alfalfa Pollinator Megachile Rotundata (Hymenoptera: Megachilidae). Annals of the Entomological Society of America, 93/4: 904-911. Accessed November 11, 2007 at http://www.bioone.org/perlserv/?request=get-document&issn=0013-8746&volume=093&issue=04&page=0904.

Peterson, S., C. Baird, R. Bitner Parma, C. Idaho. 1992. Current Status of the Alfalfa Leafcutting Bee, Megachile Rotundata, as a Pollinator of Alfalfa Seed. Bee Science, Issue 2: 135-142. Accessed November 11, 2007 at http://www.pollination.com/publications/IPSpub02.cfm.

Strickler, K., J. Vinson. 2000. Simulation of the Effect of Pollinator Movement on Alfalfa Seed Set. Environmental Entomology, 29/5: 907-918. Accessed November 11, 2007 at http://www.bioone.org/perlserv/?request=get-document&doi=10.1603%2F0046-225X(2000)029[0907%3ASOTEOP]2.0.CO%3B2&ct=1.

Tirlea, D. 2005. "Species Page-Genus: Megachile" (On-line). University of Alberta E.H. Strickland Entomological Museum Entomology Collection. Accessed November 09, 2007 at http://www.entomology.ualberta.ca/searching_species_details.php?s=26564.

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