M. (Eutricharaea)

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 : 12-14

Subgenus Eutricharaea

Diagnosis and description.

Females: In females the scopa is mostly white at least basally (often dark apically) and the sterna have distinct apical fasciae beneath the scopa (lacking in Megachile giraudi and M. hohmanni Tkalců, 1993). In a few rare cases, the scopa is orange or entirely black (some populations of M. melanogaster, M. hohmanni). The upper mandibular tooth is usually truncate (e.g. M. leachella Curtis, 1828), although it is sometimes acute (e.g. M. deceptoria; Fig. 40 ) or conversely clearly divided into two teeth [e.g. M. rotundata (Fabricius, 1787); Fig. 39 ]. In some species, such as M. orientalis, the mandible is clearly 5-toothed (Fig. 2 ). There is no visible cutting edge in the second interspace (Figs 39-41 ), in contrast to the subgenera Xanthosarus, Megachile or Anodonteutricharaea (in the latter all cutting edges are often strongly reduced); even in the third interspace, the cutting edge is often small and partly hidden behind the margin in many Eutricharaea. Males: In the Palearctic, males of this subgenus can be recognized by the following criteria: the preapical carina of T6 is mostly denticulate (weakly so in some species such as M. rotundata) and the disc of T6 covered with dense, light vestiture entirely hiding cuticula (except in some populations of M. giraudi). T7 is small and little visible. The mandible is 3-toothed, always with triangular inferior projection. In contrast to the subgenera Anodonteutricharaea and Megachile and to most Xanthosarus and Eurymella, S4 does not have a hyaline rim apically (Fig. 10 ). The front tarsi may be modified or not, and the front coxal tooth is present (although minute in the Eutricharaea apostolica group).

Species groups.

1. Megachile rotundata group ( Neoeutricharaea Rebmann 1967). Males: Gonostylus simple, not bifid apically, s-shaped in lateral view (Fig. 54 ). Front coxa with tooth. T2 and sometimes T3 with fovea laterally. Apical margin of S4 unmodified, medially without tubercule or spot of dense, golden hairs (Fig. 10 ). Pretarsal claws of all legs with two similar, thin setae (as on Fig. 4 ). Front legs modified or not. Females: T2 and sometimes T3 with fovea laterally. Ocelloccipital distance often larger than diameter of lateral ocellus. Clypeus apically with comparatively wide, impunctate margin. Scopa usually white, black on S6, sometimes also S5, rarely entirely black.

Note. This group is particularly diverse and additional species groups may be recognized for isolated, divergent species: Megachile giraudi, with a particularly long interspace 3 in the female sex (Fig. 41 ) and front basitarsus modified, with a long apical projection in the male sex; M. orientalis, with the female mandible 5-toothed with cutting edges hidden behind the mandibular margin (Figs 2-3 ) (the male is a regular member of the Megachile rotundata group); and M. hohmanni, included in a distinct, monotypic subgenus by Tkalců (1993). Another group includes species with robust, 4-toothed mandible (Fig. 40 ), with tooth one larger than the other teeth and with reduced tufts of hairs apically, approaching the condition seen in Eurymella; males of this group are mostly characterized by the strongly convex and medially produced apical margin of T5. In the Palearctic, this group includes M. communis Morawitz, 1875, M. deceptoria, M. dohrandti Morawitz, 1880, M. sedilloti, M. jakesi Tkalců, 1988, probably M. arachosiana Gonzalez, Engel and Hinojosa-Díaz, 2010 as well as at least one undescribed species. Because all these species do not have particularly distinct gonostylus, I do not recognize separate species groups for them. Of note, the Megachile rotundata group also occurs in Africa; Pasteels (1965) referred to it as the Chalicodoma malangensis group. I have examined the type material of M. malangensis Friese, 1904 (ZMHB); this species is a member of Eutricharaea and not of Paracella (= Anodonteutricharaea) as suggested by Eardley (2013).

2. Megachile naevia group. Males: Similar to males of the Megachile rotundata group, but gonostylus apically shortly bifid (Fig. 55 ). Front tarsi modified, yellowish-white. T2 with a weak fovea laterally. Females: As in the Megachile rotundata group, but mandible always red. Apical margin of clypeus straight with comparatively wide impunctate area. Ocelloccipital distance shorter than diameter of lateral ocellus. T2 but not T3 with fovea laterally.

3. Megachile leachella group. Males: Gonostylus either bifid (Fig. 56 ) with long (e.g. Megachile leachella) or short (e.g. M. walkeri Dalla Torre, 1896) preapical process, or simple (e.g. M. concinna Smith, 1879), in all cases apically with rounded emargination (Fig. 56 ). Front coxa with tooth. T2 and T3 without fovea laterally (although the corresponding area on T2 is often finely punctured and covered with brown hairs which contrast with white hairs on rest of the tergum). Apical margin of S4 either with a patch of yellow hairs medially, or a minute tubercle covered with numerous short, white hairs. Pretarsal claw with basal hair short, thickened, as in the female (as in Fig. 5 ), and api cal hair long. Front legs not modified although front tarsi sometimes yellowish brown. Females: T2 and T3 without fovea laterally (although the corresponding area on T2 is often finely punctured and covered with brown hairs which contrast with white hairs on rest of the tergum). Ocelloccipital distance commonly equal to the diameter of the lateral ocellus. Clypeus apically with narrow impunctate zone. Scopa white on S1-S5, black on S6, sometimes partly or entirely orange-red, never black on S5.

Note. Megachile ventrisi Engel, 2008, from Saudi Arabia, Yemen ( Engel and Schwarz 2011) and at least Kenya (C. Praz and L. Packer, unpublished) belongs to another African and Oriental group in which the male front tarsi are modified (the ventral surface of the first tarsal segment is concave) and the gonostylus simple but differently shaped, without apical emargination. This group was included in the Megachile leachella group (as the " argentata " group) by Pasteels (1965); it includes the African species known as M. frontalis Smith, 1853, which is a junior homonym of M. frontalis (Fabricius, 1804); " M. frontalis Smith" is a member of Eutricharaea and not of Paracella (= Anodonteutricharaea) as suggested by Eardley (2013).

4. Eutricharaea apostolica group. Males: As Megachile leachella group, with the following exceptions: gonostylus bifid apically (as in Megachile pilidens Alfken, 1924), but apex conspicuously slender and preapical process long. Front coxa with minute tooth (see comments above). Front tarsi yellowish-white. Females: As Megachile leachella group, with the following exceptions: all legs predominantly orange; terga brown; hairs on ventral side of mid and hind femora modified, short, apically thickened. M. walkeri (included in the Megachile leachella group) also has similarly modified hairs ( Engel 2008), but in M. walkeri the cuticula of T1 and T2 is orange.

5. Megachile leucomalla group. Males: Male gonostylus as in Megachile rotundata group, but bent apex longer (Fig. 57 ). Front tarsi greatly enlarged, yellowish-white. S2 and S3 (but not S4) medio-apically with dense patch of yellow hairs. T2 and T3 without clearly delimitated fovea. Pretarsal claw of all legs with two similar hairs. Females: Body length above 13 mm; punctation of mesonotum coarse and sparse, interspaces shiny and nearly as large as puncture diameters. Apical clypeal margin truncate, premarginal, impunctate zone comparatively narrow. T2 and T3 without clearly delimitated fovea.

Species composition.

This is a large and taxonomically complex subgenus in need of revision. The number of unpublished synonymies is large and a list of species is not given here. There is only one species in the Megachile leucomalla group, M. leucomalla Gerstäcker, 1869. I know one Palearctic species in the Megachile apostolica group, Megachile soikai; this species is possibly conspecific with one of the African species related to M. apostolica Cockerell, 1937 and listed by Gonzalez et al. (2010: 65). In the Megachile naevia group, I know two species: M. naevia Kohl, 1906 from the Socotra Archipelago and an undescribed species from the Arabian Peninsula, North to Israel. There are more species in the Megachile leachella group [possibly seven; see Soltani et al. (in press) for a treatment of the taxa allied to M. concinna], and a large number of species, a few of which undescribed, in the Megachile rotundata group, for a possible total of 29 species in the western Palearctic.

Biology.

Megachile rotundata, a European species introduced into North America for the pollination of alfalfa, has been studied in detail (reviewed in Pitts-Singer and Cane 2011). All species of Eutricharaea use leaf discs to build their brood cells, although M. rotundata (and M. giraudi, see below) sometimes use petal fragments and not leaves ( Westrich 1989, and references therein). In M. minutissima Radoszkowski, 1876, the cell walls are sometimes omitted when the nest is located in cavities of small diameters, so that leaf discs are only used to build the cell partitions ( Krombein 1969). The outer nest plug of M. marginata consists of a series of leaf discs covered by a layer of mud, possibly mixed with “saliva” ( Ferton 1914). Nests of Eutricharaea are mostly built in existing cavities such as stems or beetle burrows (e.g. M. rotundata), under stones or in existing cavities in the ground (e.g. M. pilidens: Müller et al. 1997; M. marginata: Ferton, 1914; M. minutissima: Alqarni et al. 2014), or more rarely in burrows dug by the bee in sandy soil ( M. leachella: Westrich 1989; note that this species may accept trap nests under artificial conditions: Holm and Skou 1972) or in hard soil ( M. deceptoria: Benoist 1940, Grandi 1961, Zettel et al. 2005, Mazzucco and Mazzucco 2007). M. giraudi appears to nest specifically in holes in rocks and to use petals for cell construction ( Maneval 1939, Banaszak and Romasenko 2001; C. Praz and A. Müller, unpublished). The description of nesting aggregations in the soil for M. leucomalla in Central Asia (Marikovsakya 1968; see also Banaszak and Romasenko 2001) likely refers to another species, probably M. communis, based on Fig. 1 in Marikovsakya (1968).

The pollen preferences of species included in the subgenus Eutricharaea are varied; most species are probably polylectic with a preference for Fabaceae (e.g. Megachile rotundata and M. pilidens: Westrich 1989; see also O’Neill et al. 2004; M. minutissima: Alqarni et al. 2014); Müller and Bansac (2004) have shown that some species have a distinct (e.g. M. apicalis) or exclusive preference for Carduoideae ( M. marginata, M. melanogaster and M. flabellipes Pérez, 1895), and in these species a modified pollen collecting device is found under the hind trochanter and femur. Soltani et al. (in press) analyzed the pollen preferences of the taxa allied to M. concinna; all taxa were polylectic, although M. leucostoma Pérez, 1907 and M. anatolica Rebmann, 1969 showed a preference for Plantaginaceae ( Linaria -type) and Lamiaceae, respectively. Two species have long and conspicuous hairs on the galea, M. dolosa Alfken, 1936 and M. posti; all known specimens of M. posti from Cyprus were collected on Noaea mucronata (Forssk.) Asch. & Schweinf. ( Chenopodiaceae) ( Mavromoustakis 1952). Strikingly similar hairs are found on the galea and first labial palpi of some Hoplitis [e.g. H. karakalensis (Popov 1936); A. Müller, pers. comm., January 2016]; this pollen collecting apparatus likely constitutes an adaptation for collecting pollen from small flowers of Chenopodiaceae ( Müller 2016).

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 38 - 41. Female clypeus and mandibles, front view. 38 Megachile (Eurymella) patellimana 39 M. (Eutricharaea) rotundata 40 M. (Eutricharaea) deceptoria 41 M. (Eutricharaea) giraudi.

Figures 2 - 3. Female mandible of Megachile (Eutricharaea) orientalis. 2 Front view; the white lines indicate the brushes of hairs in the grooves near the base of tooth 1 3 Lateral view; the cutting edge is continuous and spans the interspaces 2 - 4, although it is completely recessed behind the mandibular margin and thus not visible in front view.

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.

Figures 54 - 57. Genital capsule, lateral view. 54 Megachile (Eutricharaea) apicalis 55 M. (Eutricharaea) sp. aff. naevia 56 M. (Eutricharaea) leachella 57 M. (Eutricharaea) leucomalla.

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.