Megachile rotundata    

common name     Alfalfa leafcutter bee

Nests in existing spaces, wood cracks or spaces between lumber (Stephen & Torchio 1961).

Emerge early-late June and adult activity from early June-late September (Stephen & Torchio 1961).

Female: Body is 8-9 mm long, robust, black body and legs, brownish circular tegulae (articulate sclerite at base of the costa vein) near base of wing and yellow spurs (articulated spine). Large cheeks slightly narrower than the eyes and mouth mandibles with 4 tooth projections. Soft, downy hair (pubescence) yellowish-white and short on the face and cheeks, more elongate and white on the lower cheeks. Pubescence dense around antennae (more yellowish), sides of face, lateral and posterior thorax (shorter and yellowish) and wing bases (more yellowish). Wings are subhyaline (sub transparent). Tergum (dorsal abdomen segments) 4-6 straight in profile with short suberect hairs and abdomen segments fringed with short yellowish-white hairs. (Mitchell 1962). The scopa (pollen-collected hair basket on ventral abdomen) is silvery gray in colour unlike most other leafcutter bees that have yellow, orange, tan or black scopa (Richards 1984). Males: Body is 7-8mm long, robust, black body, brownish tegulae, front tarsi (lower segments of leg) partly yellowish with yellow spurs. Cheeks considerably narrower than eyes and mouth mandibles with 3 tooth projections. Pubescence is considerably yellow on the face and dense around antennae, lower face region and front of face. Thorax pubescence is whitish, very dense on lateral and posterior surface and both yellowish or whitish on the dorsal surface. Wings are subhyaline and appear smoky near the apex. Sterna (ventral abdomen surface) 1 4 are exposed and have punctures and appear yellowish and hyaline with dense elongate white hairs. Sternum 5 is broad, median area has short, fine and dense setae and sternum 6 has an broad short apical lobe, incurved medially. Genital armatures have gonocoxites, which narrow above the base, is compressed, has a curved down apex, tip elongate and narrow, setae projects towards the apex, dorsal lobe is broad and flat and ventral lobe is curved and slender. (Mitchell 1962

life history
This specie is quite smaller than native leafcutter species (Richards 1984). Univoltine (one generation reaches maturity per year) (Stephen & Torchio 1961) with females mating once, while males can mate several times (Richards 1984) and mating not occurring near the nest (Stephen & Torchio 1961). Nests are made from burrowing into wood, including native and artificially made burrows (Krombein et al. 1970), previously formed holes, wood cracks, spaces between lumber and preferentially narrow tunnels that approximate their body size (Stephen & Torchio 1961). Cells are constructed from oblong leave pieces to form a linear nest of several cells, filled with pasty pollen, eggs are laid and cells are capped with circular leaf pieces (Stephen & Torchio 1961). Females usually lay female eggs in the inner cells and male eggs in the outer cells of the nest Females prefer pliable and soft leaves from species including alfalfa, clover, buckwheat, roses and sage versus tough leaf plant species (Richards 1984). Originally from Europe and Asia and introduced into Canada in 1962 (Hobbs 1972). This solitary bee is valuable in agriculture as a pollinator of alfalfa (Medicago sativa) crops and is easily domesticated (Hobbs 1972, Stephen & Torchio 1961). Factors that contribute to its success in agriculture include gregarious nesting behaviour, use of man-made nests and over-wintering mature larvae (prepupa) stage (Hobbs 1972, Stephen & Torchio 1961). Also, it is more reliable than native species because a reduction in nesting habitat due to land clearing, burning and agriculture have decreased the population of some bee species, including bumble bees and native leafcutter bees (Richards 1984). When this specie was first introduced into Canada it started pollinating alfalfa at 21°C, but some individuals have evolved to start pollination at temperatures of 18°C (Richards 1984).

Not of concern because of agricultural importance.

diet info
Polylectic (collects pollen from wide range of flowering plants) but preference for pollen from alfalfa flowers suggest preferential oligolectic behaviour (Stephen & Torchio 1961). Pollen from native and introduced flowers including Asclepias, Cosmos, Lotus sp and Veronica (Krombein et al. 1970). Uses alfalfa for nest building and foraging. Also feeds on nectar (Richards 1984).

Massasauga to Vancouver, west to British Columbia (Krombein et al. 1970) and south to Washington, Oregon, California, Kansas, Missouri, Texas and Utah (Stephen & Torchio 1961).

species page authorTirlea, D.2005 

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