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

Anthony Raw

publications

Geographical distribution

Megachile is found almost everywhere there are flowering plants.  In the Americas the genus occurs from Alaska and the mid latitudes of Canada to southern Chile and Argentina and in the Andes up to 5,000 m altitude.  There are species on the islands of southern California, almost all West Indian islands and Bermuda.  The earliest known member of the genus is neotropical; from Miocene amber of the Dominican Republic (Engel 1999). 

             The intensity of collecting neotropical Megachile is still very patchy so detailed interpretations of the species’ geographical distributions are risky.  In this inventory there are only 2 species recorded from Venezuela, 16 from Ecuador, 17 from the Guianas and 19 from Colombia (Table 2).  Nonetheless, some generalizations can be made.  Of the 516 species and 30 subgenera recorded from the Americas, 386 species (75%) and 17 subgenera are restricted to the neotropics (Table 1).  Although 9 subgenera have members in both realms, only 11 species occur in both.  Some typically neotropical subgenera, like Acentron, Cressoniella, Leptorachis, Melanosarus and Pseudocentron have few species in North America.  Only 10 of the 164 species in these five subgenera occur north of Mexico.  (However, the type species of all five are the North American representatives.)  Only two subgenera are well represented in both the Nearctic and Neotropics.  The members of Chelostomoides are well represented in much of the Nearctic and in Central America and have followed the Andes to Peru.  Only Sayapis, is common throughout the Hemisphere, occurring from Canada to Argentina.

Number of species recorded

% of total

Canada

27

5·2

U.S.A.

131

25·4

Mexico

75

14·6

C America

55

10·7

West Indies

30

5·8

Colombia

19

3·7

Venezuela

2

0·4

Trinidad

6

1·2

Guianas

17

3·3

Brazil

160

31·0

Ecuador

16

3·1

Peru

39

7·6

Bolivia

62

12·0

Paraguay

49

9·5

Uruguay

4

0·8

Argentina

72

14·0

Chile

16

3·1

Table 2. The distributions of 515 extant species of Megachile of the Americas by country and region

Vagility

The habit of numerous species of Megachile to nest in abandoned beetle burrows in wood and cracks in timberwork has allowed them great vagility and some are among the most widely dispersed of any bees.  They occur on many oceanic islands, presumably because their nests were transported to them.  Ten palaeotropical species have been introduced into the West Indies during historical times where they have established populations (Hurd 1979, Raw 1985 and data presented below).  Undoubtedly the nests of these species were carried to the Caribbean on slave ships on the "Middle Passage".  Nine species are African while M. lanata is an Indian species.  Presumably the latter spread to East and West Africa by ship and crossed the Atlantic by the same means. 

             Megachile is common on other islands.  Numerous Asian and Australian species have reached Pacific islands (Michener 1965).  Several subgenera occur on the Solomon Islands, but only two reach more easterly islands.  Species of Eutricharaea and Callomegachile occur on the New Hebrides and New Caledonia, while Eutricharaea has reached Fiji, Samoa, the Ellice and Phoenix archipelagos, Tahiti and Hawaii.  Michener (1965) suggested M. (Hackeriapis) mackayensis has probably been introduced in recent times to Lord Howe Island (650 km east of Australia).  M. gentilis is native to western U.S.A. and has become established on Hawaii (Mitchell 1935: 24).  The genus Megachile does not occur in New Zealand. 

             Several species have been accidentally or deliberately introduced to new areas more recently.  The Eurasian species, M. rotundata arrived, apparently accidentally, in U.S.A. in the 1940's (Hurd 1979) and is now widespread.  In order to improve the pollination of alfalfa, it has been introduced into Chile (Stephen 1972), Australia (Winn 1988, Woodward 1994, 1996) and New Zealand (Donovan 1908).