.:: A. Raw ::.

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

Anthony Raw

Identification

Identification of the species of Megachile is difficult; a result of both the large numbers involved, the very fine differences which distinguish them and the frequent question with Hymenoptera of associating the two sexes. Unfortunately, the difficulties encountered in their identification have deterred useful investigation on the bees. As numerous species are important pollinators of many plants, botanists often collect the females. Males are less often collected, possibly because they fly more quickly and make only fleeting visits to flowers. Despite their acknowledged importance, citations in many publications are made only to generic level, reflecting the difficulties that exist in their identification (Table 3).

Publication	Number identified	Number not identified	% not identified
Cure et al 1992	4	2	33
Silveira & Cure 1993	2	3	60
Martins 1994	12	14	54
Schlindwein 1995	14	7	33
Alves dos Santos 1996�	26	12	32
Carvalho & Bego 1996	6	9	60
Zanella 2000	8	10	56
Viana & Alves dos Santos 2002	36	28	44
Aguiar & Martins 2003	1	4	80
Zanella 2003	9	8	47
Faria-Mucci et al 2003	0	6	100
R�go et al 2000, Albuquerque et al 2001	0	10	100

Table 3. Citations of Megachile species in recent surveys of Brazilian bees

In order to identify the members of this large group of superficially similar insects it is first necessary to determine the subgenera to which they belong. The two sexes of many species of Megachile are very different in appearance. Fortunately, many are adventive nesters so the nests are relatively easily obtained and the collector may rear both sexes from a nest. For several species, this method and the rare capture of a pair in copula have been the only means of associating the sexes.
For identification, even to subgeneric level, the bees must be adequately prepared. In both sexes it is essential that the mandibles be opened to expose their inner surfaces. The fore and mid legs of the males must be sufficiently spread to allow examination of the lower surfaces. Determination of the subgenera of females is often difficult if the apex of the abdomen is not opened to allow examination of the sixth sternite. The simplest method to discover how to prepare the bee is to identify freshly caught specimens. Often pollen grains obscure the scopa of the female and must be removed before its structure can be examined. The most useful keys to the identification of subgenera of neotropical Megachile are those of Michener et al (1994) Michener (2000) and Silveira et al 2002.