Prochasma Warren, 1897

Liu, Bo & Stuening, Dieter, 2024, Review of the genus Prochasma Warren (Geometridae, Ennominae, Boarmiini), with description of a new species from Hainan, South China, ZooKeys 1190, pp. 303-317 : 303

Prochasma Warren, 1897

Prochasma Warren, 1897, Novit. zool. 4: 81. Type species: Prochasma mimica Warren, 1897.

Diagnosis.

The genus Prochasma Warren currently comprises a total of eight species, including the newly described species presented in this study. These species are united by an apomorphic character, a tuft of well-developed, basally narrow, distally broad and curved, upright scales with metallic gloss on the posterior part of mesothorax in both sexes. This character is unique and distinguishes Prochasma from other genera of the tribe Boarmiini , though curved, light-reflecting scales also occur in a number of other geometrid groups; however, these scales are not arranged as an upright brush and other characters such as antennae, transverse lines, fovea (present), venation, male and female genitalia etc. are quite different. There is no genus comparable in size and pattern known to us, with which Prochasma could be confused.

Generic description.

A generic description was provided, besides the original description by Warren (1897), only by Holloway [1994] and by Sato (2019); the latter partly repeated the characters mentioned by Holloway, but added some new features. Herein, we summarize these already published characters of Prochasma , with a few corrections, and add new-found, unpublished features.

General appearance.

Tiny ennomine moths, wingspan 18-25 mm, forewing length: male 10-15 mm, female 11-16 mm, with colourful, yellow, white and black pattern, medial zone of forewings dark in most species. Head. Male antennae bipectinate, rami arising from basal end of each segment, dorsally unscaled, densely ciliate ventrally, apical one-third of flagellum non-pectinate; female antennae filiform (not “fasciculate”, as mentioned by Sato 2019: 138). Frons narrow, rather flat, smooth-scaled, palps curved upwards before frons. Proboscis short, but functional. Chaetosemata present, small, near eye-margin. Thorax. Patagia and tegulae with large, lamellar, partly elongated scales, tegulae in addition with long hair-scales. Mesothorax posteriorly (on mesoscutellum) with a tuft of large, distally curved, metallic scales in both sexes (see Sato (2019, fig. 25); also mentioned by Warren (1897) and Holloway [1994]). Forewing pale yellow or grey ( P. albimonilis ), with distinct dark markings, without fovea in males. Antemedial and postmedial lines thin, black, deeply incurved and outwardly dentate, in some species, reduced to short streaks or dots, bounded distally by a narrow or broader band of the pale ground colour (on proximal side in antemedial lines). Submarginal lines narrow, white, zigzag-shaped where visible. In forewings, the dark band on the outside of the postmedial line broad, variable individually and in different species. The dark band on the inner side of the submarginal line on hindwing also variable in breadth, sometimes narrower, sometimes extending to the costa, angled outside or reduced to a spot. Discal dot distinct or small, black, visible on both wings, but larger on forewings. Underside similar to upperside, but more blurry and paler. Legs slender, light grey, chequered dark grey or black. Index of spurs 0-2-4, hind tibia hardly swollen, with two pairs of long spurs and with a whitish scent brush in males. Venation (Fig. 1 ). R1 and R2 coincident (distal branch of R1 reduced, only R2 reaching costa), the base of the combined veins running closely parallel to vein Sc or anastomosing with it for a short distance. Other veins inconspicuous, vein 3A in hindwing absent. Folds through cells of both wings and those replacing CuP in forewings and M2 in hindwings very vague. Pregenital abdomen. Tergites and sternites not conspicuously modified. T1 and T2 sclerotized, T1 narrow, T2 of double breadth. Seventh segment distinctly narrow, eighth segment elongate. Coremata absent. Tympanal organs of moderate size, without lacinia. Setal comb present, but modified to a multi-row setal patch, with numerous small, easily detachable setae; when central setae are lost, it may look like "a pair of setal scars" (compare Holloway [1994: 269] and Sato (2019, fig. 24)). Sterno-tympanal process present, but weak, free distal portion short, not reaching the posterior margin of tympanal bulla.

Male genitalia. Uncus triangular, base broad, lateral sides almost straight or slightly rounded, with short setae dorsally, apex short and pointed or more or less narrowly elongated and pointed. Gnathos with strong lateral arms, central part strong, elongate rectangular, with rounded tip. Juxta broad, plate-like, sclerotized, with distal incision in some species or rectangular, with apex slightly narrowed. Saccus strong, triangularly more or less extended, tip rounded. Valvae elongated, parallelogram-shaped in some of the species, sclerotized costa not reaching the weak, narrowed distal part of valvae, which is covered with a moderate to weak cucullus, which is reaching widely basad. Tip of valvae rounded, rarely dorsal margin deeply excavated more basally and carrying a tuft of long, modified setae (so far only found in the new species described below). Ventral margin of valvae at 2/3 to 3/5 length with a short, tooth-like process (i.e., distal process of sacculus). The latter is built as a narrow, sclerotized band along ventral margin of valva and may sometimes be weak or even not visible; distal tooth-like process is variable in size and may rarely be short or almost absent. Basal part of valve lamina less setose and more or less membranous, bordered distally by an oblique, sclerotized ridge. Aedeagus short and stout, vesica containing a single massive cornutus, with significant variations of size and shape between different species, an important specific character.

Female genitalia. Ovipositor short, papillae anales narrow, tapering, covered with short setae. A needle-like sclerite, found between the bases of posterior apophyses in two species so far, may also turn out to be a generic feature. Anterior apophyses distinctly shorter than posterior apophyses, the latter almost double in length. Introitus bursae funnel-shaped, often large, slightly sclerotized. Colliculum absent ( Sato (2019: 141) mentions it as “developed”, but we could not confirm the presence of a typical colliculum). Posterior part of bursa copulatrix elongated, largely membranous, posteriorly with various types of specifically different sclerotizations. Anterior part of bursa membranous, slightly broader than posterior part, but no clear demarcation visible. Signum absent.

Figures

Figure 1. Wing venation of Prochasma diaoluoensis sp. nov.