Megachile (Megachile) relativa Cresson, 1878

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 : 39

Megachile (Megachile) relativa Cresson, 1878

Megachile relativa Cresson, 1878: 126 . Mitchell 1927b: 179. Jensen 2003: 195. Fultz 2005: 82. Drons 2012: 59. Megachile (Anthemois) relativa ; Mitchell 1935b: 162. Megachile (Megachile) relativa ; Mitchell 1962: 129. Butler 1965: 5. Hurd 1979: 2056. Ivanochko 1979: 153. Sheffield and

Westby 2007: 178. Scott et al. 2011: 55. Sheffield et al. 2011: 51. Kuhlman and Burrows 2017: 13. Reese et al. 2018: 22.

Delphia et al. 2019a: 25. Sheffield and Heron 2019: 70. Engel 2020: 10. Megachile aspera Mitchell, 1924: 158 .

Diagnosis. The female of M. relativa can be identified by its 5-toothed mandibles ( Fig. 7G ), yellow-orange scopal setae on S2–6, and golden pubescence on T6. The females are most similar to M. centuncularis (see M. centuncularis above). The males of M. relativa cannot be reliably separated from males of M. lapponica in Montana based on external morphology or by examining the genitalia (see Taxonomic Challenges; Sheffield & Westby 2007). Males of M. lapponica / M. relativa can be recognized by the absence of a procoxal spine, small median triangular tubercle on the clypeal margin, narrow brown to black probasitarsi ( Fig. 8A ), evenly spaced 3-dentate mandibles, and T6 with sparse setae, not tomentose. Megachile lapponica / M. relativa is most similar to M. centuncularis (see M. centuncularis above).

Notes. In Montana, this species has been collected widely but with only a few eastern localities, reflecting the general lack of collecting in the region ( Fig. 1 AD). Photographs, a full morphological description (but see Taxonomic Challenges), and notes on its biology can be found in Sheffield et al. (2011). This species readily accepts trap nests ( Jensen et al. 2003).

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.

FIGURE 7. Female Megachile characters. (A–H) Anterolateral view of mandible, (I–N) Lateral view of metasoma, tergites 4–6, (O) Lateral view of tergites on M. dakotensis, and (P) Lateral view of head with pronounced tooth on the posterior genal margin on M. pugnata.

FIGURE 8. Male Megachile characters. (A) Probasitarsus not expanded or excavated ventrally, (B) Probasitarsus widely expanded and excavated ventrally, (C–E) Anterior view of mesobasitarsus and mesotibia, (F) Lateral view of triangular metatarsomeres on M. manifesta, (G) Lateral view of quadrate metatarsomeres on M. wheeleri, (H) Ventral view of procoxal spine, longer than wide, (I) Ventral view of procoxal spine, wide and spatulate, (J–L) Dorsal view of vertex of head: (J) Ocelloccipital distance longer than ocellocular distance, (K) Ocelloccipital distance equal to ocellocular distance, and (L) Ocelloccipital distance shorter than ocellocular distance.