M. (Chalicodoma)

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 : 8-10

Subgenus Chalicodoma

Diagnosis and description.

Females: Females can be recognized by the combination of the convex, denticulate apical margin of the clypeus and the elongate mandible with a straight margin above the two apical teeth (Fig. 19 ) (rarely with minute tooth 3, e.g., in the Chalicodoma montenegrensis group). Only some species of Pseudomegachile have similarly elongate mandibles, for example Megachile ericetorum (Fig. 20 ) and M. lanata. The former can easily be separated from Chalicodoma by the different apical margin of the clypeus (Fig. 20 ) and the long ocelloccipital distance, which is markedly longer than the interocellar distance; M. lanata has a short clypeus with apical margin entire (as in Fig. 24 ), not denticulate. In some species of the Megachile cyanipennis group of Pseudomegachile, notably M. saussurei Radoszkowski, 1874, the apical margin of the mandible is nearly straight, with reduced teeth (Fig. 25 ), thus approaching the condition found in Chalicodoma. In such species however, the mandible is less elongate, with the outer margin strongly convex. In M. (Pseudomegachile) incana Friese, 1898, the mandible is 5 to 6 toothed (Fig. 21 ), and in old specimens the teeth may be little visible and the condition thus similar to that seen in Chalicodoma; as in Chalicodoma, the ocelloccipital distance is shorter than the interocellar distance in M. incana. All species of the Pseudomegachile incana group can easily be diagnosed by the large body size, the light-grey metasomal vestiture without dense tergal fasciae and the comparatively broad hind basitarsus (Fig. 27 ). Males: Males Chalicodoma fall into three distinct species groups and there are few diagnostic characters common to all. In all species the mandible is comparatively elongate, 3-toothed and without inferior projection, and the preapical carina of T6 is denticulate.

Species groups.

Tkalců (1969) and Rebmann (1970) have independently divided the subgenus Chalicodoma into the same four groups, to which they gave subgeneric rank. I recognize three groups, not four, because Megachile hirsuta, unknown to both Tkalců and Rebmann at that time, renders the distinction between two of their groups difficult in the female sex. Recognizing these groups as subgenera appears little useful for species identification in the Palearctic and I recognize them as species groups.

1. Chalicodoma montenegrensis group ( Euchalicodoma Tkalců, 1969; Xenochalicodoma Tkalců, 1971; Allomegachile Rebmann, 1970; Katamegachile Rebmann, 1970). Males: Front coxa with large, spatulate tooth. T6 with lateral tooth (Fig. 48 ) [small in Megachile rufitarsis (Lepeletier, 1841)]. T7 mostly produced to large, rounded, median tooth (Figs 15 , 48 ) (tooth small in M. rufitarsis), or trifid. Gonostylus simple, slightly broaden apically (Fig. 48 ). In this species group, the front tarsi are variously modified. Unusual characters of males of some or all species of this group are the partly exposed S5 (character not visible in Fig. 15 ), the apically strongly convex margin of S6 (Fig. 15 ), as in Creightonella, and, in some species, in the lack of hairs laterally on S8, unlike other group 2 subgenera. Females: Surface of mandible mostly dull, with few shiny ridges or punctures, except in M. rufitarsis, in which the mandible is as in the Megachile parietina group. S6 with depressed apical zone, with strong preapical carina separating the elevated, basal part from the depressed apical zone, except in M. montenegrensis Dours, 1873 and M. hirsuta, both of which have dull mandibles. In M. montenegrensis, the vertex is slightly concave laterally, a unique feature in Palearctic Chalicodoma (see Tkalců 1969).

2. Allochalicodoma lefebvrei group ( Allochalicodoma Tkalců, 1969; Heteromegachile Rebmann, 1970). Males: Front coxa without tooth. T6 with a small lateral tooth (sometimes reduced to a mere angle, as in Fig. 45 ). T7 rounded apically, unmodified. Gonostylus tapering apically, thickened preapically and without preapical, projecting lobe (Fig. 45 ). Females: Surface of the mandible covered with numerous shiny ridges and punctures (Fig. 19 ), as in the Megachile parietina group. S6 with depressed apical zone; carina separating the elevated part from the depressed marginal area interrupted medially and only visible laterally. In addition, all females of the Allochalicodoma lefebvrei group have conspicuously modified vestiture on the clypeus (Fig. 19 ) and the frons: the hairs are short, simple and bent apically ( Müller 1996). Such modified hairs are not found in the Chalicodoma montenegrensis group and only rarely found in the Megachile parietina group.

3. Megachile parietina group. Males: Front coxa without tooth. T6 without lateral tooth. T7 rounded or truncate. Gonostylus with preapical lobe (Fig. 44 ). Females: S6 mostly not divided in two zones (weakly so in some species, such as Megachile nasidens Friese, 1898), without preapical carina. Hairs on clypeus mostly branched, except in some rare species [e.g. M. marina Friese, 1911 and M. palaestina ( Tkalců, 1988)].

Species composition.

Females of this subgenus are sculpturally uniform and frequently exhibit mimetic color evolution; hidden sternites of males are mostly diagnostic but these structures have only been described for few species (e.g. Tkalců 1969, 1974). Consequently, the taxonomic status of numerous “geographic” forms within Chalicodoma remains unclear and a complete species list is not given here. In the West Palearctic, there are at least five species in the Chalicodoma montenegrensis group [ Megachile hirsuta, M. manicata Giraud, 1861, M. mauritaniae ( Tkalců, 1992), M. montenegrensis and M. rufitarsis), two to five species in the Megachile lefebvrei group [ M. heinii Kohl, 1906, known only in the female sex; and depending on the species concept adopted one to four additional, parapatric species: M. albocristata Smith, 1853, M. hungarica Mocsáry, 1877, M. lefebvrei (Lepeletier, 1841) and M. roeweri (Alfken, 1927)]; and approximately 20 species in the Megachile parietina group, of which three are undescribed.

Biology.

The nesting biology of Megachile parietina has been described in detail (reviewed in Westrich 1989 and Müller et al. 1997). This species builds exposed nests made of hard mud in rock crevices, more rarely on twigs ( Rebmann 1969, Vereecken et al. 2010). These exposed nests are particularly hard and resistant; Kronenberg and Hefetz (1984) have demonstrated that females of M. sicula (Rossi, 1794) add labial gland secretions to the mud; these secretions rapidly harden and render the nest hydrophobic. Accounts of the nesting biology of the few species of the Megachile parietina group investigated so far indicate that the cells are build in a similar way: in M. pyrenaica Lepeletier, 1841, the cells are often hidden in holes in walls or under stones ( Le Goff 2007), or placed in existing holes in steep, hard soil slopes, under overhanging rocks ( Müller et al. 1997), or as described by Fabre (1879, 1882) under the roof tiles of old barns; sometimes the nests are exposed on stones as in M. parietina (Le Goff, 2007); in M. rufescens ( Pérez, 1879) the nests appear to be mostly placed on twigs ( Fabre 1882). M. sicula builds nests both on twigs and on rock surfaces ( Kronenberg and Hefetz 1984, Vereecken et al. 2010). Few studies have documented the nesting biology of species of the other species groups: M. manicata appears to nest exclusively in existing holes in rocks ( Le Goff 2012, Gogala 2014, C. Praz, unpublished data); Le Goff (2012) described one nest containing two cells made of hard mud mixed with pebbles; the nests observed were closed with hard mud. Nests of M. lefebvrei have been described in detail by Ferton (1908, 1920); the biology of this species slightly deviates from the typical nesting biology seen in the subgenus. Females build 2-4 cells in holes in rocks; these cells have the general appearance of those built by M. parietina, thus they consist of mud mixed with "salivary secretions" ( Ferton 1908: 545), without pebbles. Once several cells are built, they are covered with a thin (1 mm), concave layer of hardened mud; this layer is located inside the hole of the rock and its outer surface is a few millimeters beneath the external surface of the rock. Subsequently, the female fills the space above the thin mud layer with a mix of pebbles and masticated plant material. According to Ferton, the masticated plant material contains salivary secretions (but no resin), and it hardens quickly. Ferton (1920) reports a nest of M. lefebvrei from southern France; the nest structure and the material used were similar but the nest had been built in an empty snail shell.

Many species of Chalicodoma, including Megachile hirsuta, M. montenegrensis, M. manicata, M. parietina, and M. pyrenaica have a distinct or exclusive preference for Fabaceae ( Westrich 1989, Müller et al. 1997, Gogala 2014, C. Praz, unpublished data). All species of the Megachile lefebvrei group are likely polylectic with a preference for Lamiaceae ( Müller 1996; C. Praz, unpublished data). The pollen spectrum of the other species remains poorly investigated.

Figures

Figures 16 - 23. Female clypeus and mandibles, front view. 16 Megachile (Creightonella) amabilis 17 M. (Maximegachile) maxillosa; the white line indicates the hypostomal tooth 18 M. (Callomegachile) sculpturalis 19 M. (Chalicodoma) hungarica 20 M. (Pseudomegachile) ericetorum 21 M. (Pseudomegachile) incana 22 M. (Pseudomegachile) sp. aff. incana 23 M. (Pseudomegachile) foersteri.

Figures 24 - 29. Female clypeus and mandibles, front view. 24. Megachile (Pseudomegachile) seraxensis 25 M. (Pseudomegachile) saussurei 26 - 29 Female hind basitarsus, lateral view 26 M. (Pseudomegachile) ericetorum 27 M. (Pseudomegachile) incana 28 M. (Eutricharaea) giraudi 29 M. (Eurymella) patellimana.

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.

Figures 10 - 15. Male metasoma, ventral view. 10 Megachile (Eutricharaea) giraudi, metasoma with four exposed sterna, S 4 without hyaline rim, T 7 small, unmodified 11 M. (Creightonella) amabilis, metasoma with six exposed sterna, S 6 with rounded, weakly sclerotized projection 12 M. (Anodonteutricharaea) sp. aff. inornata, metasoma with four exposed sterna, S 4 with apical, hyaline rim (note that S 5 - S 8 are visible in this specimen because the metasoma has been stretched) 13 M. (Megachile) ligniseca, condition as in Fig. 12 14 M. (Eurymella) patellimana, condition as in Fig. 12 15 M. (Chalicodoma) montenegrensis, S 6 partly exposed, with rounded, weakly sclerotized projection.