Megachile rotundata

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.

• Biogeographic Regions
• nearctic nearctic
  • introduced introduced
• palearctic palearctic
  • native native
• oriental oriental
  • native native
• australian australian
  • introduced introduced

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.

• Habitat Regions
• temperate temperate
• terrestrial terrestrial

• Other Habitat Features
• urban urban
• suburban suburban

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

• Other Physical Features
• ectothermic ectothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes colored or patterned differently

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.

• Development - Life Cycle
• metamorphosis metamorphosis

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.

• Mating System
• polygynous polygynous
• cooperative breeder cooperative breeder

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.

• Key Reproductive Features
• seasonal breeding seasonal breeding
• sexual sexual
• fertilization fertilization
  • internal internal
• oviparous oviparous

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.

• Parental Investment
• female parental care 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.

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.

• Key Behaviors
• arboreal arboreal
• flies
• diurnal diurnal
• motile motile
• hibernation hibernation
• solitary solitary

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.

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.

• Perception Channels
• visual visual
• ultraviolet
• tactile tactile

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.

• Primary Diet
• herbivore herbivore
  • nectarivore nectarivore

• 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.

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.

• Ecosystem Impact
• pollinates

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.

• 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 .

• 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.

Additional Links

Encyclopedia of Life

Contributors

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

References

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 .

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 .