Megachile (Eutricharaea) rotundata (Fabricius, 1787)

Pritchard, Zoe A., Ivie, Michael A., O’Neill, Kevin M. & Delphia, Casey M., 2025, A faunal treatment of the Megachile (Hymenoptera: Megachilidae) of Montana with a key for their identification, Zootaxa 5683 (1), pp. 1-51 : 44

Notes on Megachile (Eutricharaea) rotundata and introduced Megachile Species

Megachile rotundata , or the alfalfa leafcutting bee, is native to Eurasia and was detected in the U.S. in the 1930s after being accidentally introduced ( Pitts-Singer & Cane 2011). Soon after, it was propagated across the western U.S. for alfalfa seed pollination, being first noted in Montana in 1969 ( Gerber & Akre 1969). It is managed for alfalfa seed pollination widely, including in Montana. Today, among managed species, its economic value is second only to honey bees in crop pollination ( Pitts-Singer & Cane 2011).

Although M. rotundata are usually thought of as managed in agricultural fields, feral populations also exist in the wild, though floral visitation appears to primarily favor Eurasian weeds ( Jensen 2003; O’Neill et al. 2010; Pearce et al. 2012). Megachile rotundata accepts a diversity of nest materials and nesting sites ( MacIvor & Moore 2013; Sheffield 2017). In the Wolf Mountains of Montana (45.0386°N, 107.0307°W), a wild nesting aggregation was found in holes in sandstone cliffs far from alfalfa fields (ZAP pers. obs., 2019).

Stem nesting behavior in Megachile makes them more likely to be accidentally transported to new regions, as they readily nest in human-made substrates and can be transported in materials like irrigation tubing or drilled holes in wood or metal ( Russo 2016; Poulsen & Rasmussen 2020). These introductions could be an issue for native species as one study in California suggested that invasive Megachile could potentially compete with native Megachile for nesting sites ( Cane 2003).

Megachile (Eutricharaea) apicalis Spinola is an accidentally introduced species that is now established in the U.S. ( Cooper 1984; Russo 2016) and found in Montana. This species was first recorded from Montana by Kuhlman and Burrows (2017) in Missoula Co., and we record specimens from 11 counties in Montana dating from 2013 ( Fig. 1C ). It is already documented in much of the western U.S., and is associated with an invasive rangeland weed, Centaurea solstitialis L. ( Asteraceae ) ( Barthell et al. 2001; McIver et al. 2009; Sheffield et al. 2011). In Montana, Kuhlman and Burrows (2017) suggest that M. apicalis may be using Centaurea stoebe L. ( Asteraceae ), a Montana weed that is a relative of C. solstitialis .

Figures

FIGURE 1. County-level distribution of each Megachile species in Montana. Females identified as Megachile latimanus/ Megachile perihirta (and data without recorded specimen sexes) are counted here as M. perihirta as they are not distinguishable from one another in Montana. Males identified as Megachile lapponica/Megachile relativa (and data without recorded specimen sexes) are counted here as M. relativa as they are not distinguishable from one another in Montana. Mitchell county records are included on maps but not in specimen counts. Two specimens did not have county-level localities and are not included in maps but are included in specimen counts.