Xanthosarus

Praz, Christophe J., 2017, Subgeneric classification and biology of the leafcutter and dauber bees (genus Megachile Latreille) of the western Palearctic (Hymenoptera, Apoidea, Megachilidae), Journal of Hymenoptera Research 55, pp. 1-54 : 18-19

Subgenus Xanthosarus

Diagnosis and description.

Females: Most females of Xanthosarus have a typical, broad mandible (Fig. 35 ) with tooth 1 larger than other teeth, without apical brush of hairs in the grooves around the base of tooth 1. In such females there is a well-visible, continuous cutting edge in the third interspace and a partial cutting edge in the second interspace (Fig. 35 ), the third interspace is deeper than the other interspaces, and the two upper teeth close together or poorly separated, so that the mandible is not clearly 5-toothed. Such females will be easy to identify using the present key. The mandible of Megachile nigriventris Schenck, 1868 (Fig. 36 ) [and to some extend of M. willughbiella (Kirby, 1802): Fig. 37 ] is different, less robust, with the cutting edges little visible in front view; the upper tooth is broadly truncate and the condition is intermediate between the 4-toothed and the 5-toothed conditions. In all Palearctic species of Xanthosarus, the clypeus is finely and densely punctured, regularly convex (Figs 35-37 ) unlike the condition found in most females of Megachile s. str. The scopa is mostly orange-red basally, sometimes nearly entirely black ( M. nigriventris) or yellow-white on sternites 2 and 3 [e.g. M. maritima (Kirby, 1802)], rarely entirely yellowish-white. The sterna lack the apical fringe of hairs beneath the scopa, unlike in most Eutricharaea or in M. (Eurymella) patellimana. Males: In males of Xanthosarus the front coxal spine is always well developed; often there is a field of modified, short, orange bristles on the surface anteriorly to the spine, but such field may be lacking (e.g. in M. analis Nylander, 1852). The front tarsi are always yellow or white, from relatively narrow [e.g. M. analis, M. circumcincta (Kirby, 1802)] to conspicuously enlarged [e.g. M. lagopoda (Linnaeus, 1761), M. maritima]; the first tarsal segment is mostly strongly concave interiorly, except in M. analis. The mandible is either 3-toothed ( M. lapogoda, M. maritima) or more commonly 4-toothed; the inferior margin always has a pointed process directed posteriorly; in some large species, this process is particularly large and glabrous, except for some orange hairs apically. The disc of T6 is mostly not covered by white vestiture; the preapical carina of T6 is bilobed or weakly denticulate. The apical margin of T6 often lacks a lateral tooth (a small tooth is sometimes present, e.g. in M. maritima). The apex of T7 is usually produced to a small tooth medially, although the tooth is small in some species; in other species T7 is weakly trifid. The gonostylus is variable, either simple or strongly bifid, but this character does not clearly segregate groups.

Species composition.

There are at least seven species in the western Palearctic: Megachile analis, M. circumcincta, M. diabolica Friese, 1898, M. lagopoda, M. maritima, M. nigriventris and M. willughbiella. M. fulvimana Eversmann, 1852 has been mentioned from Southeastern Europe ( Banaszak and Romasenko 2001); this species is known to me only from Central Asia. M. mguildensis Benoist, 1940, from Algeria and Morocco, apparently closely related to M. nigriventris, may either represent a distinct species or merely a color morph of M. nigriventris. Özbek and Zanden (1994) further cite M. metatarsalis Morawitz, 1894 from Turkey; this species is unknown to me. The status of M. fulvescens Smith, 1853 from Sicily is unclear; it is unlikely to represent a species distinct from those listed above; its description ("the pollen brush is of golden hue towards the base, becoming bright fulvous at the apex") suggests M. maritima. Similarly, the status of M. maacki Radoszkowski, 1874 remains in doubt; Scheuchl (2006) provides a description of the male and the female and differentiates this species from M. nigriventris. However, no lectotype has been designated. Of the possible syntypes that I could examine (ISZP), one male agrees with the original description and does not appear specifically distinct from M. nigriventris. Possibly, M. maacki represents an Eastern Palearctic, geographic form of M. nigriventris. Xanthosarus appears particularly diverse in the mountains of Central Asia and in Mongolia, where several additional species occur.

Biology.

Most species of the sugbenus Xanthosarus place their brood cells made of cut leaves in underground burrows or more rarely under stones; the females appear to dig the burrows themselves ( Westrich 1989, and references therein; Hartmann and Arens 1998). Megachile nigriventris digs burrows only in decaying wood ( Westrich 1989, Dubitzky 2000, Reichholf 2002), while M. willughbiella either digs burrows in decaying wood or uses existing cavities such as vacant Anthophora cells ( Westrich 1989, and references therein; Müller et al. 1997). Megachile analis is unusual in that it uses thin bark fragments and not leaves for the construction of the cells ( Westrich 1989, and references therein); leaf discs are also used by this species.

Megachile nigriventris is likely oligolectic on Fabaceae ( Westrich 1989, Müller et al. 1997) and M. diabolica possibly on Campanulaceae ( Hartmann and Arens 1998); M. analis and M. willughbiella are polylectic but show a preference for Fabaceae and Campanulaceae, as well as for the genus Epilobium by M. willughbiella ( Westrich 1989, Müller et al. 1997). Megachile Megachile lagopoda and M. maritima are likely polylectic with a preference for Fabaceae and Asteraceae.

Figures

Figures 30 - 37. Female clypeus and mandibles, front view. 30 Megachile (Anodonteutricharaea) albohirta 31 M. (Anodonteutricharaea) thevestensis 32 M. (Megachile) versicolor 33 M. (Megachile) lapponica 34 M. (Megachile) bombycina 35 M. (Xanthosarus) lagopoda 36 M. (Xanthosarus) nigriventris 37 M. (Xanthosarus) willughbiella.