Megachile leucografa, Friese, 1908

Roig-Alsina, A. & Torretta, J. P., 2021, The leucografa species group of Megachile (Chrysosarus) (Hymenoptera: Megachilidae), Journal of Natural History 55 (7 - 8), pp. 457-470 : 459-461

M. leucografa species group

Diagnosis. Species of this group have dusky wings with dark veins and pterostigma. Females are recognised by the pointed fourth tooth of the mandible ( Figure 1 (a)), the apical margin of the clypeus with a median smooth emargination ( Figure 1 (a)), and the broad hind basitarsus ( Figure 1 (e)). Males are distinguished by the basal tuft of long, dense hairs on the inner surface of the mandible (on the condylar interspace, Figure 1 (b–d)), the emarginate and spineless preapical carina of T6 ( Figure 1 (f)), the flattened, yellowish foretarsus with a large fringe of hairs and short, broad basitarsus ( Figure 2 (b,d,f)), the broad translucent separation area of S5 ( Figure 4 (a); and Durante (1994, fig. 4), and the broad, rounded apical lobes of the postgradular area of S6 ( Figure 4 (b); and Durante (1994, fig. 5).

Species of this group share many characters with those species that have been included in Dactylomegachile , but they also share some features with the amber-winged species that have been included in Chrysosarus sensu stricto (sensu Mitchell, 1943). The diagnostic features of the leucografa group are discussed below.

Among species that have been included in Dactylomegachile , the pointed fourth tooth of the female mandible occurs only in the leucografa group, while other species with dark veins and pterostigma have a distinctly incised, or less frequently truncate, fourth tooth. A pointed fourth tooth, on the contrary, can be found among species of Chrysosarus sensu stricto, as for example in M. catamarcensis , although amber-winged species usually have a broadly truncate, low fourth tooth (which in some specimens may appear pointed due to wear).

The broad hind basitarsus of the female is characteristic of the leucografa group (2.5–2.7× as long as its maximum width in lateral view, Figure 1 (e)), and approaches the condition seen in species with amber wings (2.7–2.8×, in species such as M. guaranitica and M. concava ). In species with dark veins and pterostigma, other than those of the leucografa group, the female hind basitarsus is slender, varying from 3.1–3.2× (in species such as M. vagata Vachal and M. ctenophora Holmberg ) to 3.35× as long as wide in M. infima . Another characteristic of the leucografa group is the medially smooth, weakly concave apical margin of the female clypeus, which is denticulate in most species of the Chrysosarus lineage.

Regarding the males, the basal tuft of hairs on the inner surface of the mandible, not accompanied by any projection, is unique to the leucografa group among species with dark wings, but it occurs in some of those species with amber wings (e.g. in M. tapytensis Mitchell and M. concava Mitchell ). Usually, amber-winged species have profuse pilosity on the condylar interspace of the mandible, while dark-winged species have sparse hairs.

Features shared by species of the leucografa group with other dark-winged species are the presence of ferruginous bristles on the nearly glabrous anterior surface of the forecoxa of the male, and the presence of a distinct angle on the lower margin of the male mandible. The preapical carina of T6 is unarmed and emarginate in the leucografa group, but a similar carina can be found among dark as well as among amber-winged species, since the carina of T6 is variable in shape and ornamentation in both groups.

Females of the leucografa group are very homogeneous morphologically, and are distinguished mainly by their vestiture. Males are easier to tell apart by characteristics of the hypostomal area, the shape of the last antennal flagellomere, the length and density of the forecoxal ferruginous bristles, and their vestiture, as indicated in the diagnoses for each species below. Some male structures, like the anterior tarsus, the genital capsule, and the shape and vestiture of S5 and S6, are diagnostic for the group, and nearly identical in the three species. The male genital capsule and hidden sterna are only illustrated for M. obscurior .

Figures

Figure 1. (a) Megachile leucografa, female, clypeus and mandibles; (b) M. leucografa, male, ventral view showing pilose hypostomal area, tuft of hairs on inner surface of mandible (‘t’), and oblique row of hairs on under surface of femur (‘r’); (c) M. obscurior, male, ventral view showing glabrous, rugose hypostomal area; (d) M. rancaguensis, male, ventral view showing pilose hypostomal area; (e) M. leucografa, female, hind tarsus; lines indicate measurements of length and width of basitarsus; (f) M. obscurior, male, dorsal view of apical metasomal terga. Scale bars: a, e = 0.5 mm; b–d, f = 1 mm.

Figure 2. Lateral habitus of Megachile species of the M. leucografa group: (a). M. leucografa, female; (b) M. leucografa, male; (c). M. obscurior, female holotype; (d) M. obscurior, male; (e) M. rancaguensis, female holotype; (f) M. rancaguensis, male. Scale bars: 1 mm.

Figure 4. Megachile obscurior, male: (a) S5; (b) S6; (c) S8; (d) genital capsule, ventral view. Scale bar: 1 mm.