Please refer also to the following link for details on this group:
Colletidae (= Hylaeidae) = Link 1
Description & Statistics
Colletidae. -- The Plasterer bees and Yellow-faced bees are a primitive group with short tongues that are either bilobed at the tip or truncate.Colletidae are a small family of primitive bees that make their nests in plant stems, in burrows in the soil, or in other holes and crevices. Several species of the principal genus Hylaeus (= Prosopis) have been studied in Hawaii by Perkins (1919), who found them to live at the expense of other bees in the family, although the exact relationships were not determined (Clausen 1940/62).
Finnamore & Michener (1993) noted that in this family the glossa is widely truncated or bilobed except pointed in males of Australian genera Hemirhiza, Meroglossa and Palaeorhiza (Michener & Brooks 1984). The glossa has a transverse preapical fringe on the anterior (dorsal) surface separating the transversely annulate area from the apical hairy lobes. The preepisternal groove is usually present and extending well below the scrobal groove. North American species lack basitibial and pygidial plates except for the rare southern Diphaglossinae and Eulonchopria in Colletinae.
The wide, truncate or bilobed glossa of this family is suggestive of wasps, but this is a derived feature rather than a plesiomorphic trait retained from Speciformes. It is used by colletids to apply the cellophane-like coating of the cells in which young develop. This waterproof coating holds the liquid (nectar and pollen) provisions provided for larval food by many colletids.
The family contains ca. 2,000 species worldwide. About 150 species occur in North America (45 in Canada). There are 5 subfamilies: Colletinae, Hylaeinae, Diphaglossinae, Xeromelissinae and Euryglossinae. The Hylaeinae is found worldwide but is most abundant and diverse in Australia. It is represented in North America by Hylaeus, which contains small, slender, black (in the Western Hemisphere) species with 2 submarginal cells (perhaps 1R1+1Rs and 2Rs), usually with yellow markings at least on the face. The body is only sparsely hairy and because the female lacks a pollen-carrying scopa, pollen is carried to the nest along with nectar in the crop. Most species nest in dead hollow or pithy stems. The Colletinae occur around the world but are diverse only in the southern continents. It is represented in North America mainly by Colletes. This genus contains hairy bees, without yellow markings, and with three submarginal cells (1R1, 1Rs, 2Rs). The body shape suggests that of Andrena or Halictus; the strongly convergent eyes and rather heart-shaped face usually distinguish Colletes from superficially similar bees in Halictidae, Andrenidae, and Melittidae. Also Colletes, the only colletine genus north of Mexico and southern Arizona, differs from all other bees in having the posterior half of the fore wing being 2m-cu distinctly arcuate toward the wing margin. Females carry pollen externally, on the well-developed scopa of the hind legs (trochanter to tibia). Nests are in burrows in the ground.
In southern North America and further south large hairy bees of the subfamily Diphaglossinae occur. North American species are in the genera Caupolicana and Ptiloglossa. In Latin America small Hylaeus-like bees of subfamily Xeromelissinae are also found. They have a small scopa on the hind legs and basal metasomal sterna for external pollen transport. One genus, Chilicola, ranges to central Mexico. Euryglossinae is endemic in Australia. Species resemble Hylaeinae but usually have a wide face and the clypeus does not extend far above the level of the tentorial pits (Finnamore & Michener 1993).
Key references are Hurd (1970), Michener (1986a), Snelling (1985), Houston (1975, 1981), Dathe (1980), Warncke (1978), McGinley (1981), Ikudome (1989)
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Clausen, C. P. 1940. Entomophagous Insects. McGraw-Hill Book Co., NY. & London. 688 p.
Danforth, B.N., Sipes, S., Fang, J., Brady, S.G. 2006. The history of early bee diversification based on five genes plus morphology. Proceedings of the National Academy of Sciences 103: 15118-15123.
Michener, D. C.. 2000. The Bees of the World, Johns Hopkins University Press.
Perkins, R. C. L. 1919. The British species of Andrena and other Nomada. Trans. Ent. Soc. London (1919): 218-317.