Leafcutter and Mason Bees: a Biological Catalogue of the Genus Megachile of the Neotropics Anthony Raw

TAXONOMIC REVIEW

The genus Megachile was created by Latreille in 1802 and, as originally conceived, it was equivalent to the present family Megachilidae which comprises one of the largest groups of bees. Of the species which Latreille included in Megachile today only the European species, M. centuncularis and M. lagopoda remain.

Very soon, various authors began to divide up Latreille’s genus into new genera. The first were Anthidium by Fabricius (1804), Osmia and Stelis by Panzer (1806), Heriades by Spinola (1808) and Latreille, himself, proposed Coelioxys in 1809. Lepeletier (1841) erected the genus Chalicodoma for the species whose body shape and mandibles differed from typical Megachile, but Mitchell (1934) returned it

to the latter genus. Creightonella was created as a subgenus of Chalicodoma by Cockerell (1908a). Michener (1962) re-examined the groups and recognized the genera: Megachile are the "leaf-cutter bees" and Chalicodoma are the "mason bees".

As interpreted by Michener (2000) Megachile comprises at least 1,320 species. In such a large genus, division into smaller, manageable groups is essential in pursuing the alpha taxonomy with any confidence. Progress has been made at this level with the erection of 53 subgenera (Michener op. cit). To date, 73 divisions have been proposed. Westwood (1840) designated the European species Apis centuncularis Linnaeus as the type of the genus Megachile.

With nearly 30 publications between 1926 and 1980, Professor T. B. Mitchell has made by far the greatest contribution to our knowledge of New World Megachile. He divided the American members into subgenera (Mitchell 1934, 1935, 1935b, 1936, 1937a, 1937b, 1937c, 1937d, 1943b, 1980) and, in so doing erected 18 of the Hemisphere’s 30 subgenera. In his last work (Mitchell 1980) he divided the group into six genera, however, we still know little of the higher taxonomy of the group and these divisions are difficult to justify. All recent authors, including Professor Mitchell, cite numerous exceptions in their keys and Mitchell changed his opinion on the presence of some critical characters in several subgenera (notably Leptorachis) between 1943 and 1980. Some others have published important works on the neotropical members of the genus. The more notable are Schrottky (1913a), Friese (1911) and Hurd (1979). However, the neotropical species still present many taxonomic questions.

To date, some 560 species have been recorded from the Americas of which 516 have been allocated to 30 subgenera (Table 1). The neotropical species of Megachile comprise 397 species in 26 subgenera (Table 1). Hurd (1979) catalogued 133 members of the genus which occur in Canada and U.S.A. (as Megachile and Chalicodoma). Michener (2000) recognised 13 subgenera from North America of which 4 do not reach the Neotropics. Three are confined to the nearctic (Grosapis Mitchell, Megachiloides Mitchell and Xanthosarus Robertson), while the subgenus Megachile is holarctic. The monotypic subgenus Grosapis is nearctic, confined to the north of Mexico (Cockerell 1934: 3; Mitchell 1930: 292) and was not included in Dr. Hurd’s inventory. The number of nearctic species now stands at 128 of which 11 also occur in the Neotropics.