Lestes nigriceps Fraser, 1924

Kosterin, Oleg E., 2018, Rediscovery of Lestes nigriceps Fraser, 1924 (Odonata: Lestidae) in eastern Cambodia, Zootaxa 4526 (4), pp. 561-575 : 564-571

Redescription of Lestes nigriceps Fraser, 1924 from Cambodia

( Figs 2–6 )

Material studied. 8 ♂♂ ( Figs 3 a–b, 4–5), 2 ♀♀ ( Figs 3 c–d, 6), Cambodia, Mondulkiri Province, a grassy swamp in a large glade in an open deciduous dipterocarp forest 15 km NNE of Sen Monorom , 12.5771 N 107.2587 E, 455 m a.s.l., 27 vii 2018, O. Kosterin leg.; deposited in RMNH and the author’s collection .

Males. Head ( Fig. 4 a–b). Labium pale yellowish. Labrum, mandible bases and gena pale greenish-blue in living specimens ( Fig. 2 ), dull bluish in dry specimen ( Fig. 4 a–b); labrum with a small indistinct triangular central spot at posterior margin. Anteclypeus dull bluish-grey, postclypeus black with bluish outer corners. Rest of head black with a slight metallic-green lustre, more expressed at ocellar tubercle and between ocelli and eyes. There are narrow light brownish slanting streaks, constricted at upper 1/3, connecting antenna bases and genae, and narrow light brownish spots ventrad of central ocellus and laterad or latera ocelli. Antennae black with brownish apices of the first two segments. Eyes pale blue in livings specimen, pinkish-brown in dry specimen. Head rear side black (in living specimens pruinosed); very inner parts of head bluish.

Thorax. Prothorax black with a hardly noticeable metallic-green lustre and yellowish ventral margins; ventral parts of anterior margin of anterior lobe also narrowly outlined with yellowish colour ( Fig. 4a ). Mesostigmal plate black dorsally (including anterior triangle), pale at sides, its anterior projections pale but outlined with black ( Fig. 4a ).

Mesepisterna with dorsal halves dark: ventral 2/3 metallic dark bluish-green, dorsal 1/3 glossy black without green tint, this indistinct non-green area tapering to anterior and posterior ends ( Figs 3a , 5a ). Ventral halves of mesepisterna pale greenish in living specimens ( Fig. 2 ), yellowish in dry specimen, to form a pair of broad, even (very slightly constricted before posterior end) and conspicuous antehumeral stripes ( Figs. 3 a–b, 5). No middorsal pale streak; dorsal suture black with a strong gloss ( Figs. 3a , 5a ). Antealar sinus black. Mesepimeron black. Mesinfraepisternum and metinfraepisternum black with a pale ventral margin (greenish-blue in living specimens, Fig. 2 ; dull yellowish in dry specimens, Fig. 5 b–e).

Degree of metathorax melanisation variable ( Fig. 5 b–e). Metepisternum mostly dull greenish in living specimens ( Fig. 2 ), yellowish in dry specimen, but its dorsoanterior part occupied by black colour expanding from metepimeron ( Fig. 5 b–e). Besides there is a deep black elongate spot at pleural suture at ca 2/3 of its length ( Fig. 5 b–e). In three specimens, anterior part of ventral pale area of metepisternum isolated by a black anastomosis before spiracle ( Fig. 5 c–d), and in one specimen missing entirely ( Fig. 5e ). Metepimeron bicolorous ( Fig. 5 b–e); its anterior part black; there is a black dorsal stripe expanding posteriorly and a narrow black stripe along posterior margin and posterior part of lower margin; the rest pale (dull greenish in living specimens, yellowish in dry specimen), pale colour making a rounded projection below spiracle (well seen in Fig. 5c, d ). There is a conspicuous drop-like bright black spot in metepimeron anterioventral part, almost at lower surface (seen in Fig. 5 c–d). Ventral side of synthorax black; poststernum pale with a black anterior part, its border marked with brownish.

In addition to the above described rather steady pattern, four specimens have also additional small, irregular and variable pale spots in mesepimeron anterior part ( Fig. 5 a–c) (in three specimens) and at the anterior part of the pleural suture (in the same three and one more specimen). In one of those specimens on both sides and in another one on the right side, both pale spots are fused into a large pale ring enclosing an irregular black spot inside ( Fig. 5c ). In one more specimen there is a posterior semiring at that place (as seen in Fig. 2 b–c) on the right sides and no spots ( Fig. 5e ) on the left side.

In living specimens, the ventral part of mesepimeron and the black parts of metepisternum and metepimeron are covered with a strong pruinescence while the dorsal part of mesepimeron remains free from it and is saturated black; the mesinfraepisternus and metinfraepisternum are also variably pruinosed ( Fig. 2 ). The elongate black spots at posterior 2/3 of interpleural suture and at anterior part of metepimeron lower margin are not pruinosed and very conspicuous in living specimens ( Fig. 2 ). This pruinescence is mostly washed out by acetone and its amount left in dead specimens is variable ( Fig. 5 ), an artifact of acetone treatment.

Legs ( Figs 3 a–b, 5): Coxae inner sides black, outer sides black at middle and with conspicuous pale (bluish/ yellowish) stipes along all margins. strongly pruinosed in living specimens. Femora bluish with two black stripes, along outer side and outer half of flexor sides, dorsal side intistinctly brownish. Tibia bluish with black stripes along flexor sides, tarsi blackish with indistinct pale spots on segments, spines black.

Wings ( Fig. 4g ) hyaline; venation blackish-brown. Pterostigmata blackish brown with bordering longitudinal veins black, cover two underlying cells, 2.8 times as long as high; its costal side slightly convex. Px 10 (1 case), 11 (12 cases) or 12 (3 cases) in FW, 9 (3 cases), 10 (7 cases), 11 (5 cases) or 12 (1 case) in HW. CuP situated midway between antenodals, Ac at the second antenodal. IR 2 becomes more or less angulated at level of RP 2 origin. Origins of IR 2 and RP 3+4 separated a bit more than length of the first crossvein between them. Two intercalar sectors between IR 2 and RP 3+4 and between RP 3+4 and MA.

Abdomen ( Figs 2 , 3 a–b): sides of S1–S6 very pale greenish; S1 dorsal side brownish-black with indistinct colour margins, dorsal side of S2–S6 metallic green except for a pale ring, interrupted by a black dorsal streak, at anterior margin. Sides of S1 with a slanting black spot on either side; sides of S2 with a black dot at level of posterior end of secondary genitalia ( Fig. 5 b–e); on S3–S6 dorsal dark areas make ventral projections before posterior tergite margins which miss metallic green so black; segment joints black. S7 dorsally metallic-green for ¾ of its length, posterior ¼ black; sides black with an indistinct pale area at posterior margins. S8–S10 black; in live specimen S9–S10 strongly pruinosed ( Fig. 2 ) but this pruinescence is missed in dry specimen.

Cerci strongly bent inwards and slightly below at distal 1/3; their tips rounded (and very slightly expanding) and touching each other ( Fig. 4d, f ). Each cercus with a broad subbasal inner tooth as a skewed triangle at ¼ of cercus length, followed by an inner long trapezoid projection, with margin almost even, without obvious teeth but just coarse ( Fig. 4d, f ). These inner structures are scarcely seen in lateral view ( Fig. 4e ). Cercus yellowish with blackish brown base and subbasal tooth and black apices, border of colours indistinct; inner margin of trapezoid projection very narrowly outlined with brownish. Paraprocts long, ca 45% as long as cerci in dorsal view ( Fig. 4d ) and ca 55% in ventral view ( Fig. 4f ). Each paraproct broad in basal half, then incised at inner side before a blunt triangular inner projection, subapical inner sides truncated at ca 45 o to body axis, apices rounded ( Fig. 4 c–d, f). In two specimens, including the illustrated one ( Fig. 4 ), the inner projections of the two cerci touch each other so that the incisions of both paraprocts form an arrowhead shape ( Fig. 4 c–d, f). In eight specimens, the paraprocts are set a bit more apart so that their inner subapical projections do not touch each other, but their shape including the asymmetrical blunt triangular shape of the incision between them and the basal projection, are the same. Expanded flat apical parts of two paraprocts are not in the same plane but are oriented somewhat in a roof-like manner.

Measurements (mm). Abdomen without appendages 29.5–31.5; HW 20–22; total length 37–41.

Comparison with the lectotype of Lestes nigriceps . The Cambodian males are identical to the lectotype with respect to the shape of the anal appendages ( Fig. 1 e–f vs Fig. 4 c–f) and coloration of the synthoracic dorsum ( Fig. 1 a–b vs Figs. 3a , 5a ) but differ in a more profound melanisation of the metathorax, with the most part of the imframetepisternum and the anterior party of the metepimeron black (pale in the lectotype, Fig. 1d ) and the dorsal black stripe on the metepimeron much broader ( Fig. 5 b–e). However, the black pattern of the synthorax sides is quite variable even in the Cambodian series collected from the same swamp ( Fig. 5 b–e). Moreover, the lectotype shows no trace of pruinosity and most probably was an immature individual, so the dark pattern would possibly expand later. In spite of these colorational differences, the conspecificity of the Cambodian specimens to the lectotype of L. nigriceps is obvious.

Females ( Figs 2 b–c, 3c–d, 6) resemble males. Pale colour greenish yellow in living specimens ( Fig. 2 b–c), yellow in dry specimens ( Figs 3 c–d, 6).

Head ( Fig. 6 c–d) as in male but labrum indistinctly brownish at middle, anteclypeus brownish, pale streaks between genae and antennal bases and pale spots at ocelli broader, not constricted, there are narrow pale streaks along eye margins; occiput and rear part of head dull yellowish, with indistinct black areas at eye margins.

Thorax ( Fig. 6 a–b). Prothorax pale at sides, black dorsally, its anterior lobe with a large, anteriorly expanding black spot and a pair of small elongate black spots at its sides at lobe posterior margin; there is a tiny yellowish dorsal spot at posterior margin of posterior lobe. Mesostigmal plate dorsally black but yellowish at middle, with black marks at posteriolateral corners, anterior triangle brownish. Antealar sinus bicolorous, brownish black at tip and sides and brownish-yellow at margins and central area, transcersed by black middorsal stripe.

Mesepisternum as in male; rest of synthorax pale without pruinosity and with fine black markings as follows:

- a streak along mesopleural suture with a smooth extensions at its proximal 1/3;

- a spot in mesepimeron anterior part, large and fused with the above streak in female specimen 1 ( Fig. 6a ) and small and isolated in female specimen 2 ( Fig. 6b );

- dorsal part of mesinfraepisternum black for an area different in the two female specimens;

- a triangular spot at posterior end of pleural surture and posterior margin of mesepisternum;

- a narrow streak along metapleural suture, gradually disappearing in anterior part;

- a distinct narrow black spot in anterior part of metepimeron at its ventral margin (smaller than in male).

Legs ( Fig. 6 a–b) as in male, with black stripes narrower.

Wings as in male; female 1: antenodals FW Px (left, right): 12 and 10, HW Px: 10 and 9; female 2: 11 Px in all wings.

Abdomen: S1–S6 pattern as in male; S7 similar to S6, with posterior black patches larger ( Fig. 3 c–d); S8 black with a pale distal margin and pale posterior part of sternite; S9 black with a pair of two pale spots occupying most of posterior tergite half, separated from each other by a middorsal triangle of black and from posterior segment margin by narrow black stripes; S10 dorsal half pale with a blunt triangular posteriodorsal spot, ventral half black. Cerci pale with blackish tips, simple, conical, not appressed; paraprocts black ( Fig. 6 e–f). Ovipositor with an even, not dentate, slightly S-like curved ventral margin; the second pair of valves extends to level of S10 posterior margin, the third pair extends beyond it but does not reach level of paraproct tips; genital appendages extend beyond paraprocts but do not reach level of cerci tips. Ovipositor black, but the first pair of valves contrasted pale, bases of second pair of valves reddish-brown; tips of the second pair of valves (comprising main part of ovipositor) and visible part of the third pair of valves lighter blackish-brown at tips; genital appendages brownish with blackish-brown, slightly expanded tips ( Fig. 6f ).

Measurements (mm): Abdomen without appendages 30; HW 23; total length 39.5–40.

Short Diagnosis of Lestes nigriceps . A Lestes species with abdomen kept straight in life, with mesepisterna dorsally metallic green with a middorsal black stripe but without any pale stripe, and with a pair of even and broad pale antehumeral stripes; male synthorax beyond mesepisterna strongly but variably melanised and pruinosed, with conspicuous elongate black spots at metepimeron ventral margin anteriorly and, in males, at posterior 2/3 or mesepimeron ventral margin; male paraprocts as long as ca half of cerci, with inner margin incised and bearing blunt angular subapical projection.

Differential diagnosis of Lestes nigriceps . Lestes nigriceps belongs to a series of species which keep the abdomen straight, like the Palaearctic species, rather than curved as the species related to L. praemorsus (Selys, 1862) and the species currently attributed to Platylestes Selys, 1862 , both latter groups having different structural and colorational characters (e.g. the synthoracic marking).

The appendages of L. nigriceps resemble those of L. viridulus , ranging in the peninsular India and once recorded in the northern Thailand ( Fraser 1933; Asahina 1983). In the latter, the paraprocts are of the same relative length but their distal part is only slightly expanded ( Fig. 8 ; see also Fraser 1929: Plate II, 7; Asahina 1983: Fig. 24). Lestes viridulus also has two dorsal metallic-green stripes with even and straight outer margins on the synthorax but always separated by a pale rather than black middorsal stripe. Besides, L viridulus differs strongly from L. nigriceps in having no any dark markings on the synthorax beyond the mentioned dorsal stripes and ‘faded’ coloration of the abdominal segments, “warm reddish brown on dorsum, with a cupreous reflex” ( Fraser 1929: 849; 1933: 46).

As in L. nigriceps , males of L. malabaricus from the southern India and Shri Lanka have a strong melanisation of the synthorax, but the paraprocts are short, of a simple shape ( Fraser 1929: plate II: 6; 1933: Fig. 16; pers. comm. by N. Van der Poorten) and the outer border of the dorsal metallic dark stripe on the mesepisternum has a variably expressed posterior extension.

Of other ‘straight-bodied’ Oriental Lestes spp., L. angularis Fraser, 1929 , L. elatus Hagen in Selys, 1862 and L. nodalis Selys, 1891 (the latter peculiar in many respects) have very short male paraprocts and different coloration, L. concinnus Hagen in Selys, 1862 (= L. thoracicus Laidlaw, 1920 ;?= L. umbrinus Selys, 1891 , see Dumont et al. 2017) have no metallic dark colour on the thorax. Lestes patricia Fraser, 2914 is a peculiar large insect with a mat black thorax dorsum and non-melanised thorax sides stripes ( Fraser 1933). Lestes malaisei Schmidt, 1960 most probably belongs to Indolestes Fraser, 1922 or some other genus as follows from the very schematic illustrations in the original description ( Schmidt 1964).

Habitat. In Cambodia, L. nigriceps was found at a large, shallow grassy swamp situated in an extensive opening of a deciduous dipterocarp forest on a narrow, moderately elevated (455 m a.s.l.) plateau ( Fig. 7 ). (The satellite image of 2012 at Google Earth ® made before the construction of the road shows the opening small and hardly traceable, suggesting existence a forest swamp at that place and subsequent logging.) There L. nigriceps cooccurred with Lestes praemorsus decipiens Kirby, 1893 , but these species obviously segregated for microhabitats, for L. nigriceps preferred dense grass emerging from water and small ditches while L. p. decipiens preferred sparse grass emerging from large open pools.

During two hours of examination (9:30–11:30), this swamp revealed a very rich damselfly and dragonfly fauna (28 species), also including Aciagrion approximans Selys, 1876 (one male), Argiocnemis rubescens rubeola Selys, 1877 (few), Ceriagrion azureum Fraser, 1922 (one female), C. cerinorubellum (Brauer, 1865) (one female), C. indochinense Asahina, 1967 (very many), C. auranticum Fraser, 1922 (an uncertain sighting of a tandem), Pseudagrion australasiae Selys, 1876 , Anax guttatus (Burmeister, 1839) , Ictinogomphus decoratus melaenops (Selys, 1858) , Macromiidae indet. (one male each), Acisoma panorpoides Rambur, 1842 (few), Aethriamanta gracilis (Brauer, 1878) (one male each), Brachythemis contaminata (Fabricius, 1793) (few), Diplacodes nebulosa (Fabricius, 1793) , D. trivialis (Rambur, 1842) (few), Indocnemis carnatica (Fabricius, 1798) , I. limbata (Selys, 1891) (many), Neurothemis fluctuans (Fabricius, 1793) , N. fulvia (Drury, 1773) , Orthetrum neglectum (Rambur, 1842) (one male each), O. sabina (Drury, 1770) (few), Pantala flavescens (Fabricius, 1798) (few), Ryothemis triangularis Kirby, 1889, Tramea transmarina euryale Selys, 1878 (many), Trithemis aurora (Burmeister, 1839) (very many), T. festiva (Rambur, 1842) (many).

Distribution of Lestes nigriceps . Lestes nigriceps is known only from the type locality in Bihar State in the eastern India and now from one locality of Mondilkiri Province in the eastern Cambodia. It is hence expected to occur in the countries lying in between, Myanmar and Thailand. Since the border of Vietnam lies just 27 km to the south-south-east and 35 km to the east from the Cambodian locality, there is no doubt that the species occurs in southern Vietnam as well.

Figures

FIGURE 1. Lectotype (male) of Lestes nigriceps in BMNH (NHMUK 013384634) (courtesy of Benjamin Price) (a–g) and its drawing in the original description (Fraser 1924: plate IX: 6) (h): a—general habitus (dorsal view) and labels; b—head, thorax, left wings and base of abdomen, dorsal view; c—general habitus, lateral view; c—head, thorax and base of abdomen, lateral view; general habitus, lateral view; e, h—end of abdomen, dorsal view; c—general habitus, lateral view; f—ditto, lateral view; g—paraprocts, dorsal view.

FIGURE 2. Lestes nigriceps in nature; Cambodia, Mondulkiri Province, a grassy swamp in a large glade in an open deciduous dipterocarp forest 15 km NNE of Sen Monorom, 12.5771 N 107.2587 E, 455 m a.s.l., 27 vii 2018: a—male; b–c—tandem.

FIGURE 3. Specimens of Lestes nigriceps from Cambodia, Mondulkiri, 15 km NNE of Sen Monorom: a–b—males; bfemale 1; c—female 2.

FIGURE 4. Details of the male specimen shown in Fig. 3a of Lestes nigriceps from Cambodia, Mondulkiri, 15 km NNE of Sen Monorom: a—head, dorsal view; b— ditto, frontal view; c—paraprocts, dorsal view; d—S10 and appendages, dorsal view; editto, lateral view; f— ditto ventral view, g—left hind wing. Scale bar 0.5 mm.

FIGURE 5. Head, synthorax and S1–2 of four male specimens of Lestes nigriceps from Cambodia, Mondulkiri, 15 km NNE of Sen Monorom; a–b—the specimen shown in Figs. 3a and 4; d—the specimen shown in Fig. 3b; a—dorsal view; b–e—lateral view. Scale bar 2 mm.

FIGURE 6. Female specimens 1 (a) and 2 (b–f) of Lestes nigriceps from Cambodia, Mondulkiri, 15 km NNE of Sen Monorom: a, b—head, synthorax and S1–2, lateral view; c—head, dorsal view; d—ditto, e–f—end of abdomen,lateral view. Scale bar 1 mm.

FIGURE 7. Habitat of Lestes nigriceps in Cambodia, Mondulkiri, 15 km NNE of Sen Monorom, 12.5771 N 107.2587 E, 455 m a.s.l.: a grassy swamp in a large glade in an open deciduous dipterocarp forest, 27 vii 2018.

FIGURE 8. Anal appendages of two male specimens of Lestes viridulus (India, Karnataka, Kodagu District, Makutta, 22 iii 2013, Krushnamegh Kunte leg.) from National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore (courtesy of Shantanu Joshi): a, c—specimen PS598; b, d—specimen PS597; a, b—dorsal view; c, d—ventral view.