Megachile

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 : 16

Subgenus Megachile

Diagnosis and description.

Females: In females of this subgenus, the mandible always has a conspicuous, partial cutting edge in the second interspace (reduced in Megachile genalis, which is easy to diagnose due to the thickened buldge at the base of the mandible: Amiet et al. 2004, Scheuchl 2006), and no visible cutting edge in the third interspace (Figs 32-34 ). The mandible is mostly 5-toothed with the distance between both upper teeth subequal to the distance between the other teeth (not clearly so in M. genalis) (Figs 1 , 32 ); in some species teeth 4 and 5 are poorly separated (Fig. 33 ). In M. bombycina, the mandible is elongate and 4-toothed but the partial cutting edge in the second interspace is well visible (Fig. 34 ). In most species, the clypeus is flat or slightly depressed preapically, and there the punctures are coarse and the interspaces wide, shiny (Fig. 32 ); this condition is not found in M. lapponica Thomson, 1872, in which the clypeus is densely punctured (Fig. 33 ), and in M. bombycina, in which the clypeus is modified, short, laterally truncate and medially produced to a blunt triangular process, and with its apical margin forming a wide, smooth and slightly concave area (Fig. 34 ). In the female sex, many species of Megachile s. str. are sculpturally similar to Anodonteutricharaea; in the former, the scopa is mostly orange basally and rarely white, while in Anodonteutricharaea the scopa is mostly white to yellowish white; and Anodonteutricharaea can be distinguished by the presence of two unmodified setae on the pretarsal claws; in Megachile s. str., the basal seta is modified to a thicken process, as in Eutricharaea or Xanthosarus (as in Fig. 5 ). Males: Males of the subgenus Megachile s. str. are rather homogenous both in their sculpture and in genitalic structures, and often difficult to identify. All males of the subgenus Megachile s. str. lack a front coxal spine, although in some species ( M. ligniseca, M. melanopyga Costa, 1863), the front coxa forms a weak angle. The mandible is always 3-toothed, mostly with inferior projection (lacking in M. pilicrus and M. armenia Tkalců, 1992). In most species the disc of T6 is devoid of white or light pubescence (except in M. pyrenaea Pérez, 1890, M. armenia, M. pilicrus and M. melanopyga), the preapical carina of T6 is never denticulate, although there is a lateral tooth at the lateral margin of T6 (Fig. 42 ). T7 is either small or exposed, but mostly unmodified (without tooth apically). The gonostylus is always simple, never bifid apically (Fig. 42 ).

Species composition.

There are at least 14 valid species in the Western Palearctic: Megachile alpicola Alfken, 1924, M. armenia, M. bombycina, M. calloleuca, M. centuncularis (Linnaeus, 1758), M. genalis, M. lapponica, M. ligniseca, M. melanopyga, M. melanota Pérez, 1895, M. octosignata Nylander, 1852, M. pilicrus, M. pyrenaea and M. versicolor. I have not been able to locate the type of M. dacica Mocsáry, 1879; Schwarz et al. (1996) and Westrich (2011) recognized this species as valid; in contrast, according to identified material in his collection (OLML), B. Tkalců considered Megachile dacica as a valid subspecies of M. lapponica. The status of M. melanota is unclear, as it may represent a dark color form of M. octosignata.

Biology.

All species are leafcutters and build brood cells made of leaf fragments (e.g. Malysheva 1958, Westrich 1989, Ruhnke 2000); no Palearctic species appears to use petals as documented in the Nearctic Megachile montivaga (Michener, 2007, and references therein; Orr et al. 2015). The nests are mostly located in existing, above-ground cavities; some species such as M. centuncularis are flexible and nest both in above-ground cavities and in the soil ( Westrich 1989, and references therein). Nests of M. pyrenaea and M. octosignata are placed under stones or in the soil ( Ferton 1909, Grandi 1961, Westrich 1989), and a nest of M. melanopyga was found "loose in the grass" ( Friese 1898). M. genalis exclusively nests in standing stems, favoring fresh stems, thus from plants of the same year; the female digs an opening and places the brood cells vertically above or below the entrance ( Ruhnke 2000, and references therein). According to a brief account by Friese (1898), M. pilicrus nests in dry stems of thistles.

Most species of the subgenus Megachile are polylectic, often with a preference for Fabaceae and Asteraceae ( Westrich 1989). Megachile lapponica is an oligolege on Epilobium ( Westrich 1989, Kühn et al. 2006), while M. genalis is possibly oligolectic on Asteraceae ( Westrich 1989); M. pilicrus is oligolectic on Carduoideae and its hind trochanter and femur are covered by modified, stiff hairs, as observed in some Eutricharaea species specialized on these plants ( Müller and Bansac 2004).

Figures

Figure 1. Female mandible of Megachile (Megachile) centuncularis; the white lines and the numbers indicate the five teeth (numbers on the right) and the four interspaces (numbers on the left); in this species, there is a partial cutting edge in the second interspace and, in front view, no visible cutting edge in the other interspaces. Picture by Andreas Mueller (Mueller et al. 1997).

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.

Figures 4 - 7. Claw of hind leg of females; the white lines show the basal seta; the seta is considered elongate in 4, 6 and 7 and modified to a thick process in 5. 4 Megachile (Pseudomegachile) ericetorum 5 M. (Eutricharaea) deceptoria 6 M. (Eurymella) patellimana 7 M. (Anodonteutricharaea) thevestensis.

Figures 42 - 49. Apex of male metasoma; 42 - 46, 48 T 5 - T 7 and apex of genital capsule, dorsal view 47 T 5 - T 7 and apex of genital capsule, lateral view 49 T 4 - T 6, dorsal view 42 Megachile (Megachile) melanopyga 43 M. (Pseudomegachile) sp. aff. incana 44 M. (Chalicodoma) parietina 45 M. (Chalicodoma) hungarica 46 M. (Creightonella) albisecta 47 M. (Creightonella) doriae 48 M. (Chalicodoma) manicata 49 M. (Eurymella) patellimana.