Leafcutter and Mason Bees: a Biological Catalogue of the Genus Megachile of the Neotropics Anthony Raw
Download 0.92 Mb.
|
GEOGRAPHICAL DISTRIBUTIONMegachile is found almost everywhere there are flowering plants - on all tropical and temperate continents and on many oceanic islands between 50o N and S. Species are distributed from 45oS to 65oN and from up to 5,000 m altitude in the tropics. However, most of the world’s subgenera have relatively restricted distributions. In the Americas Megachile occurs from Alaska and the mid latitudes of Canada to southern Chile and Argentina. However, 75% of the 516 species are restricted to the neotropics (Table 1). Species also occur on the islands of southern California, almost all West Indian islands and Bermuda. The intensity of collecting neotropical Megachile is still very patchy so detailed interpretations of the species’ geographical distributions are risky. For example, in this inventory there are only 2 species recorded from Venezuela, 16 from Ecuador, 17 from the Guianas and 19 from Colombia (Table 2). However, some generalizations can be made. So far as is known 17 of the 30 subgenera are restricted to the neotropics and 4 to the nearctic. 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 taxa are well represented in both the nearctic and the neotropical regions. The members of Chelostomoides are well represented in much of the Nearctic and in Central America and have followed the Andes to Peru. Only one subgenus, Sayapis, is common throughout the Hemisphere, occurring from Canada to Argentina. Table 2. The distributions of 515 extant species of Megachile of the Americas by country or region
Vagility The habit of numerous species of Megachile to nest in abandoned beetle burrows in wood and cracks in timberwork has given them great vagility and some members of the genus 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 on coastal ships and thence crossed the Atlantic by the same means. Megachile is a frequent member of other island faunas. 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 also reaches 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). Hawaii has also received the American species, M. gentilis which is native to western U.S.A. and has become established on the islands (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) and Australia (Winn 1988, Woodward 1994, 1996). Download 0.92 Mb. Share with your friends:
|