Alfalfa Leafcutter Bee

Alfalfa leafcutter bees (Megachile rotundata) are so named because the bees make their nests from circular disks cut from plant leaves, often from the alfalfa plant (Medicago sativa), by the bees' mandibles. This bee is native to Eurasia, but was introduced to North America sometime after the 1930's; it is now feral and widespread in the United States and northern Canada. Alfalfa leafcutter bees are 1/4 to 3/8 of an inch long. They are black with whitish or yellowish bands on their abdomens. Alfalfa leafcutter bees have been used as commercial pollinators of alfalfa for over 50 years. They also pollinate carrot (Daucus carota), onion (Allium spp.), and wild blueberry (Vaccinium spp.) crops as well as sweet clovers (Melilotus spp.), white clover (Trifolium repens), and some wild mints (Mentha spp.). Stiff hairs on the bee's abdomen collect pollen during foraging. This pollen is then inadvertently transferred to other flowers while the bee continues to forage.

Several factors make the alfalfa leafcutter bee a good commercial pollinator. These bees are easy to manage, requiring only moderate time and money, and are non-aggressive. Although they are solitary nesters, they are gregarious so females nest in groups and they can be induced to nest in artificial nesting sites like drinking straws or drilled blocks of wood. These bees are easily transported during the immature stage and colony size grows rapidly. Additionally, they forage close to their nest sites, usually within a few hundred feet of the nest, and will remain primarily in the field to which they are supplied. Finally, they have a long field life of up to nine weeks. Alfalfa leafcutter bees have been managed as commercial pollinators for several crops. Since the 1950's, this bee has been used commercially to pollinate alfalfa (Medicago sativa) crops and they are now used in Oregon, Washington, Idaho, Montana, and Nevada. California is also looking into using alfalfa leafcutter bees as commercial pollinators for its alfalfa crop. These bees have a preference for alfalfa and visit flowers in rapid succession, at the rate of about eight to 15 flowers per minute. They can shorten the pollination season of alfalfa by several weeks, leading to decreased pesticide applications and irrigations late in the season and lowering pest pressures that can plague alfalfa crops late in the season. Each female is capable of pollinating enough alfalfa to generate 1/4 pound of seed. Since the 1990's these bees have also been used as pollinators of wild blueberry (Vaccinium spp.) fields and have a pollination success rate of over 85% in these fields. These bees are preferred over honey bees (Apis mellifera) when it comes to pollinating blueberry fields because alfalfa leafcutter bees have an affinity to the blueberry flower and forage in the field where their nest is placed, whereas honey bees have a low preference for blueberry flowers and an extended flight range. Additionally, alfalfa leafcutter bees are now used as pollinators of greenhouse carrot crops, and one alfalfa leafcutter bee can do the job of 20 honey bees.