Microstigmus lydiae, Field, 2023

Field, Jeremy, 2023, Description and nesting biology of three new species of neotropical silk wasp (Hymenoptera: Apoidea: Pemphredoninae: Microstigmus), Journal of Natural History 57, pp. 1-18 : 9-11

Microstigmus lydiae sp. nov.

Recognition

This species has the female 3rd antennal segment (i.e. the first flagellomere) relatively long and thin, like M. mirandae sp. nov., but differs from M. mirandae sp. nov. in: (1) darker overall colouration of head and thorax, with a thick black line along top edge of clypeus ( Figure 1 (d)); (2) mesopleurae lacking striations latero-ventrally; (3) presence of short striations at back of scutum at high power ( Figure 2 (b)). (4) Anterior face of male antennal scape pale yellow, contrasting with white lower face and mandibles; (5) surface of male second tergite smooth, without depressions or grooves.

Description

Female. Length 4 mm. Colouration: head black except lower face across most of its width, and a narrow line adjacent to the inside of the eyes, pale orange ( Figure 1 (d)). Dark orange strip running around back of head, connecting back of eyes to occipital carina, present in some specimens. Clypeus pale orange but always with a thick, black line along upper edge ( Figure 1 (d)). Mandibles creamy white, noticeably whiter than yellowy scape, with dark red-edged tips. Antennae yellow beneath, brown above, darker towards the tips. Pronotum orange with anterior dark mark centrally and dark brown areas on underside of pronotum in some specimens. Scutum with thick central orange-yellow strip running antero-posteriorly, approximately one-third the width of the scutum. Laterally, each side of this strip dark brown/black ( Figure 1 (b)). Scutellum and metanotum pale orange, each with central black area, the two areas merged, the black areas less extensive laterally than in M. mirandae sp. nov. or M. rosae sp. nov. Mesopleurae pale brown with small yellow-orange area postero-centrally. Underside of mesothorax dark brown/black. Propodeum (including sides) and abdomen black/dark brown, with a pale mark on each side at the base of the second tergite. Variable pale marks on sternites in some specimens. Legs pale yellow-orange except coxae and trochanters yellowy-white beneath, and hind femora with variable amounts of dark brown, especially dorsally.

Maximum width of face across the eyes approximately 1.1 times the distance from top of the head to apex of clypeus when head is viewed face-on. Inner margins of compound eyes approximately parallel on face; minimum interorbital distance (across middle of face) approximately 1.1 times interorbital distance near top of the eyes. Ocelli in a not quite equilateral triangle, with the posterior side shorter and the two posterior ocelli separated by a distance approximately equal to their diameters. Mandibles with upper tooth shorter than lower tooth. Malar space longer than in M. rosae sp. nov., 1.3 times the width of antennal segment 3. Clypeus raised, anterior margin weakly convex. Basal flagellar segments of antennae longer and thinner: fifth antennal segment 1.5 times longer than wide; 3rd segment 2.1 times longer than wide and viewed from above, third segment similar in length to pedicel ( Figure 3 (b)). Integument predominantly shining. Frons finely reticulate with sparse, shallow punctures. Scutum impunctate, finely reticulate, with striations along the posterior margin visible at high power, these striations short (length less than 10% of the length of the scutum) and sparse ( Figure 2 (b)). Pronotum with a transverse carina centrally. Scutellum moderately raised centrally. Raised area with a very slight depression centrally and a short, raised longitudinal keel centrally in the posterior half of the raised area; weaker carinae each side. Metanotum with a sharp, raised longitudinal keel centrally. Mesopleurae smooth and shining, lacking latero-ventral striations posteriorly, or with at most one or two weak striations. Omaular sulcus and hypersternaulus well developed, the former wide. Propodeum shining and coarsely sculptured.

Pilosity: compound eye bare, top of head and dorsal mesosoma with dense, short setae visible at high power. In perfect specimens there are two longer, erect setae in the ocellar area, these being relatively shorter than in M. rosae sp. nov., approximately the same length as the distance between the centres of the posterior ocelli. Clypeus and lower edge of mandibles with longer setae. Antennae covered with dense, short setae, especially towards the tips. Dorsal area of propodeum bare, but posterior face with moderately dense setae, these longer than on head and mesosoma. Mesopleurae with short setae, these becoming denser and longer towards the venter and beneath. First two abdominal tergites almost bare, with short setae becoming denser towards the tip of the abdomen, including a few longer setae at the posterior edges of tergites and sternites.

Male. Similar to female except somewhat paler colouration: top of head dark brown/ black, but underside of head pale, with orange strip running around back of head, connecting back of eyes to occipital carina. Underside of mesothorax and mesopleurae paler brown than in female, and yellow-orange central area of mesopleurae larger than in female. Lower face of male is snowy white, starting half way down the eyes and including the clypeus and mandibles (except edges of mandibular tips dark red). Anterior (ventral) side of scape yellow, contrasting with the white lower face and mandibles. Malar space noticeably longer than in the female, nearly twice as long as the antennal pedicel. Male posterior tergites bear central depressions. When the abdomen is in its natural position (segments telescoped), these appear as small, groove-like depressions in the centres of tergites 3–7, the overall impression being of a central flattening of the entire posterior dorsal abdomen. The surface of tergite 2 is smooth, without depressions or grooves. Tergite 7 is black, concolorous with the other tergites, and has a small, triangular, nick-like emargination at the centre of its posterior margin. Sternite 7 narrowing towards its triangular, upturned tip.

Type material

Holotype female. ′ ECUADOR: Pichincha Province: Santa Lucia nr Nanegal (1900 m). Cabana N 0.11843 W 78.61186. 29/8/2014 J.P.Field ̍ with ′8̍ additionally pencilled onto the label (NHM).

One female and one male paratype also deposited at NHM: the male has the same data as the holotype except date is 23/8/2014, altitude 1700 m, ′Under sign̍, pencil label ′2 ̍. The female is ′ ECUADOR: Pichincha, Mashpi Reserve nr Pacto (1337 m) . N 00°09.771 ̍ W 078°52.271, 18–24/9/2014 R .Bonifacii̍, pencil label ′106̍.

Two further female paratypes have the same data as the holotype except different date/pencilled numbers (27/ 8–3/9/2014, numbers 7 and 11), and a further male paratype is: ′ ECUADOR: Pichincha, Mashpi Reserve nr Pacto (1337 m) . N 00°09.771 ̍ W 078°52.271, 24/3/2017 R .Bonifacii MS 966̍. These last three paratypes are currently in the author̍s collection but the intention is to deposit them at NIBEQ once a visit to Ecuador is possible, post-Covid pandemic .

Etymology. This species is named after Lydia Field, whose enthusiasm for the rainforests of Ecuador has been infectious.

Biology. Approximately 30 nests of this species were located. Nests ( Figure 4 (b)) were found only at higher altitudes (1000–2000 masl), principally at Santa Lucia and only rarely at Mashpi and Maquipucuna. Nests were found hanging under the leaves of a variety of plants and from man-made structures. Nests were typically brown in colour with a rough external appearance, apparently constructed from tiny pieces of plant material (such as wood fragments) interwoven with strands of silk. The nest entrance is located at the apex, where the petiole meets the main nest structure, and the lower part is divided into between 1 and 15 vertically orientated cells, visible externally as bumps on the surface of the nest. The nest entrance diameter was 2–2.5 mm and the nest petiole was straight or occasionally slightly curved, and shorter (7–8 mm, mean 7.5) than in M. mirandae sp. nov. Each nest cell contained a single offspring or was empty. Approximately 50% of nests contained more than one adult female, with up to six females and six males per nest. Offspring were provisioned progressively with leafhopper nymphs ( Cicadellidae ). Cells sometimes contained pupae of braconid wasps ( Heterospilus: Marsh and Melo 1999 ).

Figures

Figure 1. (a) Microstigmus mirandae sp. nov., dorsal view of female with (inset) whole body; (b) M. lydiae sp. nov., dorsal mesosoma of female; faces of females: (c) M. rosae sp. nov., (d) M. lydiae sp. nov. with arrow indicating dark line along top edge of clypeus,(e) M. mirandae sp.nov.; (f) face of male M. mirandae sp. nov. Scale bars: 0.5 mm.

Figure 2. Electron micrographs showing dorsal view of mesosoma and propodeum of female (a) Microstigmus rosae sp. nov., (b) M. lydiae sp. nov., (c) M. mirandae sp. nov.; (d) lateral mesosoma of M. mirandae sp. nov. female. White arrows in a–c indicate striations along posterior edge of scutum. Scale bars: 0.3 mm.

Figure 3. Electron micrographs showing antenna of female (a) Microstigmus rosae sp. nov., (b) M. lydiae sp. nov., (c) M. mirandae sp. nov. White brackets indicate antennal segment 3 (i.e. the first flagellomere). Scale bars: 0.2 mm.

Figure 4. Nests of (a) Microstigmus rosae sp. nov., (b) M. lydiae sp. nov., (c) M. mirandae sp. nov. Arrows indicate nest entrances. (a) and (b) are in situ beneath leaves of Xanthosoma sagittifolium. The scale in (c) is millimetres. Photo credits - (a) and (b): R. Bonifacii; (c) C. Savill and J. Field.