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

Anthony Raw

publications

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.  Westwood (1840) designated the European species Apis centuncularis Linnaeus as the type of the genus Megachile.  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 genus Megachile as "leaf-cutter bees" and Chalicodoma as "mason bees".  However, on a global scale there are many exceptions which cast doubt on the division between Megachile and Chalicodoma.  Therefore, in recent works Professor Michener (Michener et al 1994, Michener 2000) has combined the two taxa in a single genus and in the present work I have followed this concept of the genus. 

According to Professor Michener (2000: 67) cited 1,095 species of Megachile world-wide.  I feel he was being cautious.  At the start of the present work I compiled a list of 2,645 specific names.  Professor Michener listed 366 species from the Americas (74% of the present total). 

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.  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. 

The known distributions of several species are questionable.  Examples are Megachile (Austromegachile) antiqua , M. (Austromegachile) exaltata , M. (Austromegachile) montezuma , M. (Chrysosarus) vestis , M. (Neochelynia) aegra , M. (Neochelynia) chichimeca, M. (Pseudocentron) prietana and M. (Sayapis) zaptlana.  Even in Brazil there are some surprising distributions.  M. (Acentron) eburneipes is recorded from southern states north to Mato Grosso and Minas Gerais and from Rio Grande do Norte.  The data on these species suggest there has been inadequate collecting or patchy geographical distributions or misidentifications. 

To date, 515 species of the Americas have been allocated to 30 subgenera (Table 1).  The neotropical species of Megachile comprise 395 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 130 of which 11 also occur in the Neotropics.  An additional 90 names in Megachile have been recorded from the Americas, but the whereabouts of the types are not known. 

Subgenus

Restricted to neotropics

Both realms

Restricted to nearctic

Total Americas

Total neotropical

Acentron

21

1

 

22

22

Argyropile

 

2

6

8

2

Austromegachile

37

 

 

37

37

Callomegachile

4

 

 

4

4

Chelostomoides

16

1

17

34

17

Chrysosarus

51

 

 

51

51

Cressoniella

19

1

 

20

20

Dasymegachile

13

 

 

13

13

Eutricharaea

2

1

2

5

3

Gronoceras

1

 

 

1

1

Grosapis

 

 

1

1

0

Leptorachis

38

 

 

38

38

Litomegachile

1

 

5

6

1

Megachile

   

5

5

0

Megachiloides

   

59

59

0

Melanosarus

10

1

11

10

Moureapis

30

   

30

30

Neochelynia

17

   

17

17

Pseudocentron

68

2

3

73

70

Pseudomegachile

1

   

1

1

Ptilosaroides

2

   

2

2

Ptilosarus

15

   

15

15

Rhyssomegachile

3

   

3

3

Sayapis

21

3

6

30

24

Schrottkyapis

1

   

1

1

Stelodides

1

   

1

1

Trichurochile

3

   

3

3

Tylomegachile

6

   

6

6

Xanthosarus

   

15

15

0

Zonomegachile

3

   

3

3

Total

384

11

120

515

395

Percentage

74,6

2,1

23,3

   

Table 1. The extant species of Megachile of the Americas arranged by subgenus