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).
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