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Megachile rotundata (Family Megachilidae)

Alfalfa Leaf Cutting Bee

Distribution

Distribution:

The Alfalfa Leaf Cutting Bee is found in the Lucerne-growing areas of South Australia and New South Wales. It is an introduced species from Canada and New Zealand (SA, NSW).

Features:

Females and males are black. Females are up to 10mm long, with pale hair on the face. The mesosoma has long white hair except for the upper surface, which has very sparse hair. The metasoma has a patch of white hair on each side of the first segment, white fringes on the other segments, and the tip is black. The scopa is white.

Males are up to 8 mm long, with off–white to beige hair on the face and white fringes on the metasomal segments. The fore legs are not flattened, expanded or patterned.

Ecology/Way of Life:

Females construct thimble-shaped nest cells from oval and circular leaf pieces. They naturally nest in old borer holes, disused mud wasps nests and hollow twigs, but will also utilise nail holes, narrow tubing and folded fabric. They adapt readily to trap nests. Males fly around the nest sites. Usually there is one generation per year, they overwinter as larvae. The onset of warmer weather induces pupation and adult emergence occurs about 3 weeks later.

Preferred Image

Interaction with Humans/Threats:

Megachile rotundata is not a native bee, it has been introduced into Australia to improve pollination and seed set of lucerne crops. It is native to Europe and central and southern Asia. It was accidentally introduced into the USA, became established there and spread into Canada. Megachile rotundata was successfully introduced into New Zealand. It is now found on all continents except Antarctica.

Attempts were made to introduce the bees to South Australian lucerne-growing areas in late 1980's – 1990's. These were not successful. In 1997 bees from New Zealand were released into crops at Mathoura, NSW. In 1998 bees from Canada were released near Forbes NSW, and in 1999 at Mathoura and Ginninderra, ACT. Survival and reproduction of these bees was very poor.

Changes in techniques led to much greater survival of bees introduced from Canada in 2000 – 2001 to the above sites and new sites at Wagga Wagga and Cooma.

The spread and effects of alfalfa leafcutting bees are currently being monitored.

Other Comments:

This species belongs to the bee family Megachilidae. Megachilid bees are solitary, ie. each female builds and provisions her own nests, there is no cooperation with other females. Females transport pollen in a scopa (a patch of hairs modified to carry pollen) on the underside of the metasoma; this feature is unique to megachilids. There are a few parasitic megachilids which lay their eggs in other bees¿ nests. In Australia the family can be divided into three groups based on their nesting habits: leafcutter bees, resin bees and wood-boring bees.

In America these bees were recognised as efficient pollinators of lucerne, crops with M. rotundata producing a much higher yield of seed than lucerne pollinated by honey bees. Honey bees learn to rob lucerne flowers from the side, without touching the anthers or stigma. This way they avoid being tapped on the head when the pollination mechanism is triggered, as a result the flowers are not pollinated. Leafcutters go straight in and pollinate the flowers while collecting nectar and pollen.

In North America alfalfa leafcutting bees were 'domesticated'. Artificial nesting sites or 'domiciles' – large frames containing thousands of appropriately sized tubes – were provided for the bees close to the crop. Techniques were developed to collect and store nest cells during the winter, and control development so that adult bees emerged to coincide with crop flowering. The leafcutting bee is now the major pollinator of lucerne crops in the USA and Canada.

Megachile rotundata was named by Fabricius as Apis rotundata. The name is based on Latin, rotundus meaning round or circular.

Further Reading:

Introducing the Alfalfa leafcutting bee, Megachile rotundata (F.) (Hymenoptera: Megachilidae) into Australia – A case study. Ron M. Bittner and Stephen S. Peterson, International Pollination Systems USA. Website: http://www.pollination.com/publications.cfm

Evaluation of Quarantine risks associated with importations of the leafcutting bee Megachile rotundata to Australia from Canada. D. Anderson, 1997. Report on consultancy commissioned by Australian Quarantine Inspection Service, 56 pp.

Manitoba Forage Seed Association. (2003). Pollination & Leafcutting Bees. www.forageseed.mb.ca/

Acknowledgments:

Text and image of plant damage from Dr Glynn Maynard. Image of Megachile rotundata copyright CSIRO. Specimen images of Megachile rotundata copyright Museum Victoria. These specimen images were kindly provided from the Pest and Diseases Image Library (PaDIL)

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Images and Multi-media:  
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image/gif 60134 bytes Megachile rotundata (leaf-damage)
Distribution Map  
image/jpeg 44870 bytes Distribution of Megachile rotundata
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image/jpeg 44683 bytes Megachile rotundata
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image/jpeg 35297 bytes Megachile rotundata (Female)
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image/jpeg 28760 bytes Megachile rotundata (Female lateral view)
Attached Image  
image/jpeg 33010 bytes Megachile rotundata (Male)

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