Megachile rotundata (Alfalfa leaf cutter bee)
Megachile rotundata is in the family Megachilidae. The genus Megachile is known by the common name “leaf cutter bees” because many members cut out circular or oval pieces of leaves and use them to line their nests. There are some exeptions; some Megachile use tree resin and others use chewed vegetation and mud in addition to leaf pieces. M. rotundata is a fairly common leaf cutter bee in Bee Atlas blocks in southern Minnesota, and all nests we found were in USDA hardiness zone 4b.
Megachile are primarily characterized by having large chewing mandibles and scopae (pollen-collecting hairs) on the underside of females' abdomens. Megachile rotundata, like many Megachile, is a mostly dark bee with light hair bands across the abdomens of both females and males. Males have unmodified forelegs and look similar to females with extra long antenna and no scopae. Bees range from 7-9 mm long. Megachile rotundata is a fairly small robust bee, half as long as a honey bee worker. They look similar to other Megachile species, but if you can get a good look at a pollen-less scopa from behind and underneath, you can see that below the longer light-colored scopal hairs, there is a second band of short, dense hairs along the edge of each abdominal segment, between the bands of long scopal hairs. Megachile rotundata are introduced to North America from Europe and are managed as an important pollinator of alfalfa.
Megachile rotundata use leaf pieces to build their nests and nest plugs. You can frequently see overlapping leaf pieces in a plug and leaf pieces will often have visible veins. They also sometimes use petal pieces to build their nests.
M. rotundata most frequently nested in lower column 3 (3/16") holes in Bee Atlas blocks, but also sometimes used larger diameter tunnels. (see graph in pictures)
Reports from one Bee Atlas volunteer with an alternative nest trap suggest 2 generations per year are possible.
M. rotundata is most active in the later summer. Most M. rotundata nests in the Bee Atlas project were completed in August. (see graph in pictures)
No information at this time.
Minnesota Record Map
These data are from the Minnesota Bee Atlas project.
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