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.

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 Herein, we summarize these already published characters of Prochasma, with a few corrections, and add new-found, unpublished features.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.

Figure 1. 

Wing venation of Prochasma diaoluoensis sp. nov.

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.

Holotype : male, China, Hainan Province, Lingshui, Diaoluoshan, 922 m, 20.IV.2023, Bo Liu leg. DNA barcode CRICATAS00001 (CRICATAS/ IZCAS). Paratypes (67 males, 7 females): 13 males 3 females, same locality and collector as holotype, 20.IV.2023, gen. prep. no. CRICATAS00064; 39 males 4 females, same locality and collector as holotype, 10.V.2023, gen. prep. no. CRICATAS00063, gen. prep. no. CRICATAS00071; 6 males, same locality and collector as holotype, 19.VI.2023; 9 males, same locality and collector as holotype, 19.VIII.2023. (CRICATAS/ IZCAS/ ZFMK).

Figures 2–7. 

Adults of Prochasma diaoluoensis sp. nov. 2 male, holotype, upperside 3 male, holotype, underside 4 female, paratype, upperside 5 female, paratype, underside 6 male, paratype, living specimen 7 female, paratype, living specimen. Scale bar: 1 cm.

Prochasma diaoluoensis is distinguished from its congeners by the following characteristics: 1) Valvae with a deep excavation on dorsal side near apex, basally adjacent a brush of modified setae present, absent in other species (Sato 2023, in litt.); 2) Apex of uncus very short, not narrowly elongated; 3) female genitalia with an elongate, funnel-shaped, sclerotized structure on posterior part of bursa copulatrix and a spoon-shaped lamella postvaginalis; and 4) Ante- and postmedial lines reduced to small denticles, bordered by broad, white lines, more conspicuous than in the congeners. The latter two features are found, but less expressed, also in some other species. The same can be stated about the horizontal, yellow band, traversing both forewings, which is most conspicuous in P. mimica, less conspicuous in diaoluoensis, but often present, at least in traces, also in the other congeners. Generally, the new species is, though more vividly coloured and with more strongly contrasting pattern, rather similar to its congeners, with exception of P. albimonilis which lacks the yellowish ground colour and has homogenous, dark grey pattern elements, almost not separated into basal, medial and postmedial areas. The female genitalia of albimonilis are similar to P. diaoluoensis in the posterior part of bursa, which is also roundly extended on right side, but the sclerotized part is not funnel-shaped but rather broadly tube-like (Sato 2019, fig. 40). It may even be a functional colliculum. In male genitalia, a narrow dorsal incision is present near apex of valvae in albimonilis, but the valvae are broader, especially the sclerotized costal side, and more densely setose.

Forewing length : male 12.2–13.2 mm; female 12.9–13.6 mm. Head. Antennae bipectinate on basal two-thirds in males, rami long, length of longest rami about 9 times the diameter of the flagellum segments, filiform in females. Frons not protruding, covered with short scales, upper half pale, lower half dark. Labial palpus curved upwards beyond frons, covered with intermingled, dark and pale scales and longer hair-scales. Vertex with pale scales, a few dark scales near antennae. Thorax. Patagia and tegulae with lamellar, dark and pale scales, with longer, dark hair-scales on tegulae only, ventrally thorax covered with pale yellow hair-scales. Legs slender, pale, chequered black, hind tibia slightly dilated, with a pale scent brush in males. Forewings with apex angled, termen smoothly curved, without fovea in males. Hindwing with apex rounded. Wings yellow, covered with extensive black scales. Fringes with alternating yellow and smaller black parts. Forewing yellow, with distinct dark markings. Antemedial and postmedial lines both appear as consisting of a few black denticles or dots between M₁ and CuA₂, bordered by a broad, white band. In females, the denticles are more tooth-like. Submarginal line white, very fine, zigzag-shaped. Area between M₃ and CuA₁ appears as a yellow, horizontal band, with or without a few small black spots. Discal dot oval, black, faintly visible. Dark band on inner side of postmedial line of hindwing narrow, reaching from discal dot to inner margin. Dark band on outside broader, the width variable between individuals, slightly broader in females. Submarginal line visible, intermittent, weaker in hindwings. Underside similar to upperside, but more blurry and paler. Venation (Fig. 1). Forewing: R₁ and R₂ coincident; R₁+R₂ arising from upper vein of cell, then shortly anastomosing with Sc, and running almost parallel to the long stem of R_3-4; stem of R_3-5 arising shortly before anterior angle of cell; M₂ from the middle of the discocellulars; CuA₁ from before posterior angle of cell. Hindwing: Sc+R₁ running closely parallel but not anastomosing with upper vein of cell at base; Rs from before anterior angle of cell; CuA₁ from before posterior angle of cell; 3A absent. Pregenital abdomen. Dorsally scaled pale yellow, with a large black spot on each tergite. Ventrally with pale yellow hair-scales. Tympanal organs and a modified setal comb present, the latter as described in the generic description. Tergite and sternite of segment 7 short, length about 2/5 of width. Tergite and sternite of segment 8 elongate, length slightly greater than width in males, broader in females.

Figures 8, 9. 

Male genitalia of Prochasma diaoluoensis sp. nov. 8 paratype (vesica partly everted), gen. prep. no. CRICATAS00063 9 paratype (brushes of modified setae removed, vesica not everted), gen. prep. no. CRICATAS00064. Scale bar: 1 mm.

Male genitalia. Uncus triangular, base broad, with short setae dorsally, apex very short, not narrowly elongated. Gnathos with strong lateral arms, central part strong, rectangular, with rounded tip. Juxta rectangular, sclerotized, apex slightly narrowed. Saccus V-shaped, slightly extended. Valvae elongated, apically narrowed ventrally, tip rounded, with a deep excavation on dorsal side. Valve lamina proximally membranous, distally densely covered with setae, without a typical cucullus, with an oblique, sclerotized ridge between both parts. A tuft of long, curved, modified setae, tubular at base, distally flattened, present dorsally near the apex of each valva. Costa straight, sclerotized, basally slightly broadened, distally not reaching tip of valva, ending at excavation. Sacculus sclerotized, distally with a short, tooth-like process, protruding from ventral margin of valva at ¾ of its length. Aedeagus cylindrical, apically broadly elongated and sclerotized on one side. Cornutus short, not stick-like, apex tapering, with bulbous base.

Female genitalia. Ovipositor short, papillae anales narrow, tapering towards apex, covered with short setae. Anterior apophyses short, about 2/3 length of posterior apophyses. A thin needle-like sclerite, roundly enlarged anteriorly, present between the bases of posterior apophyses. Lamella postvaginalis large, spoon-shaped. Introitus bursae funnel-shaped, slightly sclerotized. Posterior part of bursa elongated, membranous, distally roundly extended on right side; outside with a posteriorly funnel-shaped sclerotized structure formed by a broad sclerite which consists of lamellar plates folded three times, with unknown function (see Figs 11–14). Anterior part of bursa slightly broader than posterior part, but no clear demarcation visible. Signum absent.

Figures 10–14. 

Female genitalia of Prochasma diaoluoensis sp. nov. 10 paratype, gen. prep. no. CRICATAS00071 11–14 Close-ups of lamella postvaginalis, introitus bursae and posterior part of bursa 11 ventral view 12 dorsal view 13 lateral view from right side 14 lateral view from left side. Scale bars: 1 mm.

The specific name is derived from the type-locality, Diaoluoshan, Hainan Island, China.

China (Hainan).

Preliminary phylogenetic estimations

A barcode sequence based on the COI (658 bp) was obtained from the holotype of P. diaoluoensis and submitted to BOLD Systems (BIN: BOLD: AFJ0024, Sample ID: CRICATAS00001, Process ID: CCLEP001-23). There are currently 14 (including the one for P. diaoluoensis) Prochasma-associated DNA barcoding records on BOLD Systems. Four of them are private and restricted to use only within BOLD Systems, and the remaining ten published records are available but contain nonidentifications and misidentifications. On the basis of the images of the specimens provided on BOLD, the locality information attached to the records and the provided barcode data, most specimens could be identified to species level. However, three species (P. mimica, P. dentilinea, P. parasqualida) are still not represented on BOLD, so a full phylogenetic analysis of the genus is not yet possible. However, based on the data currently available, the following preliminary conclusions can also be drawn: The neighbour-joining tree of Prochasma (Fig. 15) clearly shows that P. diaoluoensis is a distinct species and most closely related to P. albimonilis, with a mean genetic distance of 7.05% (p-dist) (Table 1). Interspecific genetic distances range from 4.9% to 8.7%, intraspecific values range from 0.3% to 2.0%. Furthermore, a phylogenetic tree, offered and constructed by BOLD Systems and based on the sequences of the “100 nearest neighbours”, i.e., the species most closely related to P. diaoluoensis, showed that all sequenced Prochasma species clustered into a single clade of the phylogenetic tree. This is consistent with the results of our morphology-based study (see generic description and diagnosis). The three not yet sequenced species (i.e., P. mimica, P. parasqualida, P. dentilinea) largely agree with the morphological characters of the others and will not change the homogenous character of the cluster, then representing the genus Prochasma.

Table 1.

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Genetic distances (p-distance) within and between species of the genus Prochasma.

		1	2	3	4	5	6	7	8	9	10
1	P. diaoluoensis-CRICATAS00001
2	P. albimonilis-BC ZSM Lep 57402	6.8%
3	P. albimonilis-BC ZSM Lep 57403	7.3%	0.6%
4	P. squalida-BC ZSM Lep 52239	7.4%	7.8%	7.8%
5	P. squalida-BC ZSM Lep 52240	7.8%	7.8%	7.4%	0.3%
6	P. ? sasakiana-BIOUG12334-B09	7.3%	7.8%	8.2%	7.6%	7.6%
7	P. ? sasakiana-BIOUG12334-C05	7.3%	7.8%	8.2%	7.6%	7.6%	0.0%
8	P. kishidana or nr.-BC ZSM Lep 69051	7.8%	8.1%	8.2%	7.8%	7.8%	4.9%	4.9%
9	P. kishidana-BIOUG12315-G07	7.6%	7.3%	7.5%	8.2%	8.2%	5.6%	5.6%	3.3%
10	P. kishidana-BC ZSM Lep 07934	8.1%	7.9%	8.4%	8.7%	8.7%	5.6%	5.6%	2.9%	2.0%

Figure 15. 

Neighbour-joining tree of Prochasma taxa on the basis of DNA barcoding.

India.

Only three specimens are known so far (collection of Natural History Museum, London). Sato (2019) figures a male and a female syntype (figs 1, 2) and male and female genitalia of syntypes (figs 27, 28).

Myanmar, Laos, Vietnam.

Sato (2019) figures the male holotype from NE Myanmar (fig. 5), a male and a female from Vietnam (figs 22, 23) and their genitalia (figs 36, 40).

India, Nepal, Myanmar, Thailand, Laos, Vietnam, SW. China (Han H. Beijing, pers. comm.).

Sato (2019) figures a male syntype from Naga Hills, E. India (fig. 3) and three males and one female from Nepal, Vietnam and Myanmar (figs 7–10), genitalia of male syntype (fig. 29), male and female genitalia from Myanmar (figs 30, 37).

Peninsular Malaysia, Borneo (Brunei, Sarawak), Sumatra.

Specimens from Borneo have earlier been treated as P. dentilinea Warren (Holloway [1994], fig. 574, male genitalia, pl. 17, fig. 36, male adult). Both clearly belong to P. kishidana. The female genitalia (fig. 578) is different to those figured by Sato (2019, figs 38, 39) for kishidana and sasakiana, and may belong to a third, still unknown Bornean species, or the difference may be due to geographical variation, as Sato’s figure represents a female from Sumatra.

Vietnam, Laos, Thailand.

Considered as conspecific with P. squalida in Sato (2019, 2020).

Borneo (Sabah).

Occurring together with P. kishidana on Borneo.

China (Taiwan).

This species had been sunk as a synonym of Prochasma dentilinea by Prout (1927), but was restored to a valid species by Sato (2019). Specimens from Vietnam, Laos and Thailand identified as conspecific with P. squalida in Sato (2019, 2020) were separated and treated as a new species, P. parasqualida in Sato (2023).