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Leafcutting Bees


There are two main managed bees in Manitoba; the honey bee (Apis mellifera) and the alfalfa leafcutting bee (Megachile rotundata). Although they are both bees that can be managed, there are in fact few similarities in how they are managed. The long and warm summer days that are characteristic of Manitoba provide favourable conditions for the management of both honey bees and alfalfa leafcutting bees.

Alfalfa leafcutting bees, through their pollination of alfalfa that is grown for seed, contribute to the annual production of approximately 1,500 metric tonnes of alfalfa seed in Manitoba. Average alfalfa seed production is about 200-300 kilograms per hectare. Alfalfa leafcutting bees can also pollinate crops such as birdsfoot trefoil, as well as lowbush blueberry and hybrid canola.

In addition, surplus alfalfa leafcutting bees are sold to alfalfa seed producers in the United States and other markets. Average bee return at the end of the season is approximately 150-200% of the number of bees put out in the field. Bee return and seed production can be highly variable depending on the weather.

There are about 80 alfalfa leafcutting bee producers in Manitoba and the majority of them are also alfalfa seed growers. The stocking rate on alfalfa seed is generally 20,000-30,000 or more bees per acre.

Unlike honey bees, alfalfa leafcutting bees do not function as a colony, but rather they are "solitary bees". Many alfalfa leafcutting bees can occupy a single shelter, however each female works her own nest space and forages independently. Alfalfa leafcutting bee producers provide nest blocks, which the females use to lay their offspring, inside shelters. The shelters are evenly spaced throughout the alfalfa seed field (ex: 1 shelter per 3 acres).

Managed alfalfa leafcutting bees in Manitoba generally have one generation per year. They are normally active from mid-late June to mid-late August and live for approximately 6-8 weeks.

The alfalfa leafcutting bee enters winter as a mature larva (a.k.a. prepupa) (i.e. the offspring produced in the summer) in a cocoon. Each cocoon is constructed with about 15 leaf or petal pieces that show the colours of the plant from which they were cut. The bee is stored over winter in cool storage and emerges as an adult in late spring after about 3-4 weeks of controlled incubation.

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