Ostrovus kyushuensis, Hanada, 2025

Hanada, Satoko, 2025, A new species of the genus Ostrovus Ricker, 1952 (Plecoptera: Perlodidae) from northern Kyushu, Japan, with notes on the male drumming signal, Zootaxa 5653 (3), pp. 324-342 : 326-339

Ostrovus kyushuensis sp. nov.

( Figs. 1–21 )

Ostrovus sp. : Hanada 2014: 18–19; Hanada 2016: 17. Type series. Holotype male: Magaribuchi, Sawara Ward, Fukuoka City, Fukuoka Prefecture, Japan, 33.495356, 130.296219, alt. 232 m, 4.V.2013. Paratypes: 1 male, the type locality, 13.IV.2013; 1 male, the type locality, 19.IV.2014; 1 female with eggs, the type locality, 29.IV.2017; 1 female, the type locality, 24.IV.2019; 1 male, 1 female with eggs, collected by light traps, Kasuga Valley , Yoshida , Ureshino Town, Ureshino City, Saga Prefecture, Japan, 33.023222, 130.034528, alt. 442 m, 25. V.2000 .

Other specimens examined. The type locality: 1 female, 13.IV.2013; 1 male, 19.IV.2014; 1 male, 1 female, 26.IV.2014; 1 male (a mature nymph collected on 21.IV.2015 and emerged on 22.IV.2015); 1 male, 3. Ⅴ.2015; 1 female, 28.IV.2019. Hoshino Village , Yame City, Fukuoka Prefecture, Japan, 33.216944, 130.809167, alt. 396 m : 1 female, 1.IV.2021; 1 female, 1.IV.2022. Fujiwara , Mitsuse Village, Saga City, Saga Prefecture, Japan, 33.441719, 130.309589, alt. 480 m : 1 female, 20. V.2017. Ikisa , Ouchi Town, Karatsu City, Sage Prefecture, Japan, 33.369611, 130.048722, alt. 314 m : 1 male, 22.IV.2018; 1 male, 18.IV.2021; 1 male, 1. V.2021. Yamase , Hamatama Town, Karatsu City, Saga Prefecture, Japan, 33.372358, 130.055717, alt. 410 m : 1 male, 29.IV.2018; 1 female, 23. V.2021. Kasuga Valley , Yoshida , Ureshino Town, Ureshino City, Saga Prefecture, Japan, 33.023222, 130.034528, alt. 442 m : 1 male, 3 females (one female with eggs), collected by light traps, 25. V.2000; 1 female, collected by light traps, 2.VII.2000.

Adult habitus. Wings macropterous in both sexes; male body length 10.1–12.8 mm (mean ± SD = 11.6 ± 0.9, n = 10), female body length 10.5–15.5 mm (mean ± SD = 13.4 ± 1.5, n = 12); male forewing length 12.0–14.0 mm (mean ± SD = 13.2 ± 0.6, n = 10), female forewing length 13.0–15.0 mm (mean ± SD = 14.0 ± 0.6, n = 13).

Head dark brown ( Fig. 1 ), or dark brown with pale brown areas near the ocelli and on the occiput; the pale brown areas variable in shade and extent, frequently indistinct; obscure darker markings at the back of each posterior ocellus ( Fig. 2 , arrows); M line indistinct ( Fig. 2 ). Compound eyes and three ocelli black. Antenna dark brown; scape darker than the rest of the segments. Ventral surface of the head is dark brown. Labial palpus and maxillary palpus are brown.

Pronotum rectangle with rounded anterolateral angles and slightly curved anterior edge, wider than long, bearing an elliptic groove along the edge, dark brown with a pale brown or yellow-brown median band, or uniformly dark brown; near anterior and posterior margins of the groove darker in color; worm marks few and indistinct ( Figs. 1 & 2 ). Meso- and metanotum dark brown, sometimes with a pale-colored median narrow line on mesonotum and a pale-colored spot on metanotum. Mesosternum is typical for the genus presented by Ricker (1952).

Wings blackish except the whitish yellow costal region ( Fig. 1 ). Longitudinal veins C and Sc and crossveins between C and Sc whitish yellow; other veins dark brown. Wing venation shown in Fig. 3 : 2–7 crossveins (3–7 in forewing, 2–5 in hindwing) between C and Sc besides humeral cross-vein (h); 1–4 crossveins (2–4 in forewing, 1–4 in hindwing) between C and R 1; RS branches 2 or 3 times.

Coxae and trochanters pale yellow. In fore and mid legs, femora and tibiae brown to dark brown except the pale yellowish basal two-fifths (range: 1/5–3/5) of femora, however, tibia of mid leg rarely with a pale yellowish area on the distal half; femur and tibia of hind leg pale yellow except the brownish distal two-fifths (range: 3/10–7/10) of femur and except the brownish basal three-tenths (range: 1/10–1/2) of tibia, however, tibia of hind leg rarely without the pale yellowish area. Tarsi and claws brown. Cercus dark brown, 9–12 segmented; length of cercus 3–4 mm.

Male. Abdominal terga 1–7 unmodified, mostly brown with slightly darker areas on either side and the middle except terga 1–3 or 1–2 with a pair of small, whitish, weakly sclerotized areas. Tergum 8 with a long, truncated projection well over the anterior border of tergum 9 ( Figs. 4 & 5 ); the projection apex with shallow emarginate tip ( Fig. 5 ). Anterior margin of tergum 9 with a weakly sclerotized semi-elliptical area, occupying about one-third of the width of tergum 9 ( Figs. 5 & 6 ). Tergum 10 incompletely divided; the both sides of the cleft forming hemitergal lobes ( Fig. 5 ). Paragenital plate short ( Fig. 5 ). Paraproct expanded and protruded dorsally, looking like bearing a small concave at the base in lateral view ( Figs. 5 & 7 , arrow). Terga 8–10 and paragenital plates and paraprocts dark brown except the basal area of the projection of tergum 8 and the weakly sclerotized area of tergum 9, being whitish. Abdominal sterna 1–6 unmodified and dark brown. Sterna 7 with a small ventral lobe, produced caudally ( Fig. 8 , vl). Ventral lobe on sternum 8 absent ( Fig. 8 ) or slightly suggested. Sternum 9 long, covering the anterior part of sternum 10; its posterior margin parabolic ( Fig. 8 ). Sterna 7–10 dark brown except the central whitish area of sternum 10. Aedeagus short and completely membranous; everted aedeagus with a pair of small ventral lobes near the base and with two bulges at the top ( Fig. 9 ). Epiproct composed of an epiproct tip, a lever arm, a basal anchor and a lateral arm, and lateral stylets absent ( Figs. 10–13 ): epiproct tip composed of a large and well sclerotized frame-shaped median support with a semicircular dorsal top and a beak-shaped apex in lateral view ( Figs. 4 & 10 middle & 11) and with a lateral membranous expansion on the either side on the median support ( Figs. 10 upper, lower & 11); lever arm stout and strongly curved ( Fig. 11 ); basal anchor somewhat rounded and transparent except the brown basal area connected the lateral arms ( Figs. 12 & 13 ); lateral arm large and bilobed ( Figs. 11 & 13 ).

Female. Abdominal terga brownish except terga 1–3 or 1–2 bearing a pair of whitish, small, weakly sclerotized areas. Abdominal segment 8 swollen on both posterolateral sides ( Fig. 14 ). Abdominal sterna pale yellow; subgenital plate pale yellowish brown and sometimes partly brownish; the dorsal of subgenital plate having a small whitish semicircular area, near the vulva ( Fig. 15 , arrow with an asterisk). Subgenital plate large, and slightly longer than sternum 9, with a shallow midline concave ( Figs. 14 & 16 ). A pair of pale yellowish brown sclerites located on sternum 9, near the vulva ( Fig. 16 , arrows).

Egg. Pale yellow, turtleback-shaped with a rounded fingernail-like collar ( Fig. 17 ). Anchor located the ventral side of the collar ( Fig. 17 lower). The egg is morphologically indistinguishable from that of O. mitsukonis (see Isobe 1997: figs. 11A–C).

Drumming signals. Two of the three observed males displayed drumming behavior. One reared 11-day old and one captured 6-day old male produced calls by tapping the ventral lobe upon the recording chamber substrate (see Figs. 4 & 8 , vl). The male call patterns were composed of alternate short and long beat intervals ( Fig. 18 ). Since the short beat intervals had consistent inter-beat intervals with a 9.9 ms mean interval difference calculated by subtracting minimum mean interval from maximum mean interval (95.1 ms of G3–85.2 ms of G1 = 9.9 ms≤10 ms) ( Fig. 19 ), they were considered intra-group intervals. Thus, the male call of the new species was described as a grouped bi-beat call signal pattern.

Most of the beat groups consisted of 2 beats and had 90.2 ± 7.3 ms intra-group intervals ( Fig. 19 , Table 1). However, beat groups 1 and 2 were sometimes aberrant, consisting of only one beat (45% and 10%, respectively). The male call signals were composed of 9–15 groups per signal (mean ± SD = 11.8 ± 1.7) with somewhat consistent 140.6 ± 22.7 ms inter-group intervals ( Figs. 18 & 20 , Table 1).

The amplitudes of beats were low at the beginning of the signal (around the beat groups 1–5) and then gradually increasing ( Fig. 18 ). The inter-group interval showed a tendency to be unstable at the beginning of the signal (igi1–igi2) and then to be slightly longer with signal progress ( Fig. 20 ). The mean interval difference of inter-group interval was 63.7 ms (194.5 ms of igi14–130.8 ms of igi3 = 63.7 ms) ( Fig. 20 ). Total signal duration and total number of beats per signal averaged 2533.0 ± 505.9 ms (range: 2017.3–3639.7, n = 20) and 23.1 ± 3.6 beats (range: 16–29, n = 20), respectively.

Ecological notes. The new species inhabits the upper reaches of rivers ( Fig. 21 ). Adults were found in spring and early summer (April–July).

Distribution. Japan (northern Kyushu).

Etymology. The species name refers to Kyushu, one of the Japanese main islands from which the holotype was collected. Japanese common name: Nishi-kogusa-himekawagera.

Remarks. The characteristics of the new species and two known species of the genus Ostrovus , O. mitsukonis and O. nikkoensis are summarized in Table 2 and Table 3. As for O. nikkoensis three females from Nasushiobara City, Tochigi Prefecture, near the type locality of O. nikkoensis , were compared with the digital images of the type and agreed with the type in the following characteristics (see Table 2): the color pattern of the head in dorsal and ventral (see Figs. 23 & 25 ); the pronotum with a yellowish brown band (see Fig. 23 ); the colors of the scape and the pedicel (see Figs.24 & 25 ); the large subgenital plate with a median shallow concavity (see Fig. 44 ); the forewing length (the type: 14.5 mm, the three females: 14.0 mm, 14.8 mm, 15.3 mm). Therefore, I identified the three females as O. nikkoensis . Additionally, ten males collected with the three females likely also represent O. nikkoensis , their morphological characteristics being shown in Table 2 and 3 and depicted in illustrations based on these males.

Male epiproct of each species in Ostrovus shows species-specific characteristics ( Table 2, Figs. 10 , 34 & 42 ), and moreover, the shape of the weakly sclerotized area at male abdominal tergum 9 ( Figs. 5, 6 , 28 & 40 ) and the shape of the male paraproct ( Figs. 7 , 29 & 41 ) are also probably species-specific. In contrast, the characteristics of the projection on male abdominal tergum 9 ( Figs. 5 , 27 & 38 ), especially the shape of the tip and the width, could be varied even among individuals of the same species ( Figs. 27 , 30–33 , 38 & 39 ).

Females of the three species have similar large subgenital plates ( Figs. 16 , 36 & 44 ). Therefore, examinations must include multiple characteristics to distinguish the species: color patterns of the head and antenna (especially the pedicel) and the pronotum ( Table 2). However, the color on the dorsal surface of the head in both sexes is somewhat variable, and sometimes the light-colored areas are darker and thus indistinct. Forewing length and the index of distance between compound eyes / width of a compound eye in dorsal view could be helpful to distinguish O. mitsukonis from the other two species ( Table 3).

Ricker (1952) described the probable male of O. nikkoensis based on a single male specimen from Ogawa, in the southern part of Shinano Province (the present Nagano Prefecture or Gifu Prefecture), Honshu, Japan. By Ricker’s illustration, the male has a weakly sclerotized area at abdominal tergum 9, whose shape is a transversally narrow band approximately 2/3 as wide as tergum 9 (see Ricker 1952, fig. 75). The characteristic disagrees with those of the three species of Ostrovus (see Table 2), and therefore the male is probably an undescribed species of Ostrovus .

Figures

FIGURE 18. A male call signal of Ostrovus kyushuensis sp. nov., composed of 13 beat groups. G = beat group.

FIGURE 19. Intra-group interval patterns of grouped male call signals in Ostrovus kyushuensis sp. nov. Circles = means, vertical solid line = standard deviation, number above the standard deviation = number of intra-group intervals, G = beat group.

FIGURE 20. Inter-group interval patterns of grouped male call signals in Ostrovus kyushuensis sp. nov. Circles = means, vertical solid line = standard deviation, number above the standard deviation = number of inter-group intervals, igi = inter-group interval.

FIGURE 21. The type locality of Ostrovus kyushuensis sp. nov.

FIGURES 34. Male epiproct tip of Ostrovus mitsukonis. Dorsal view (upper), and lateral view (lower). Scale: 0.1 mm.

FIGURES 42. Male epiproct tip of Ostrovus nikkoensis. Dorsal view (upper), and lateral view (lower). Scale: 0.1 mm.

FIGURES 1–3. Adults of Ostrovus kyushuensis sp. nov. 1. Habitus (a paratype female), dorsal view. 2. Head and pronotum (the holotype male), dorsal view. Arrows = obscure darker markings. 3. Right wings. C = costa, h = humeral crossvein, R1 = radius 1, Rs = radial sector, r-m = radiomedial crossvein, Sc = subcosta. Scales: 1 mm (Figs. 2 and 3).

FIGURES 4–9. Males of Ostrovus kyushuensis sp. nov. 4. Terminalia with an exposed epiproct, lateral view. 5. Terminalia with an exposed epiproct (ventral aspect), dorsal view. 6. Tergum 9 of a paratype male collected from Yoshida, Ureshino City, Saga Prefecture, Japan. 7. Right paraproct, right lateral view. 8. Terminalia, ventral view. 9. Everted aedeagus, ventrolateral view (left) and ventral view (right). Roman numerals indicate abdominal segments. ep = epiproct, la = lateral arm, pg = paragenital plate, pp = paraproct, vl = ventral lobe. Scales: 1 mm (Figs. 4–6, 8 and 9); 0.5 mm (Fig. 7).

FIGURES 10–13. Males of Ostrovus kyushuensis sp. nov. 10. Epiproct tip, dorsal view (upper), lateral view (middle) and ventral view (lower). 11. Whole shape of an epiproct, caudo-lateral view. 12. Basal anchor of epiproct with the right lateral arm and a part of the lever arm, ventro-lateral view. 13. Cleared terminalia (tergum 10, lateral arms and a basal anchor of the epiproct), dorsal view. ba = basal anchor, et = epiproct tip, la = lateral arm, le = lever arm, T10 = tergum 10. Scales: 0.5 mm (Figs. 10–13).

FIGURES 14–17. Female and egg of Ostrovus kyushuensis sp. nov. 14. Terminalia, ventral view. Roman numerals indicate abdominal segments. 15. Sternum 9, ventral view, with the subgenital plate turned over.Arrows = a pair of sclerites; arrows with an asterisk = a whitish area; v = vulva. 16. Subgenital plate, ventral view. 17. Egg, dorsal view (upper) and lateral view (lower). a = anchor, c = collar. Scales: 1mm (Figs. 14 and 15); 0.1 mm (Fig. 17).

FIGURES 22–25. Ostrovus spp. 22. Head and pronotum of Ostrovus mitsukonis (male), dorsal view. 23. Head and pronotum of Ostrovus nikkoensis (female), dorsal view. 24.Antennal segments 1–4 of Ostrovus nikkoensis, dorsal view. 25. Head of Ostrovus nikkoensis (female), ventral view. Arrows = brown postgenae. Scales: 1 mm (Figs. 22, 23 and 25); 0.5 mm (Fig. 24).

FIGURES 43–44. Females of Ostrovus nikkoensis. 43. Terminalia, ventral view. 44. Subgenital plate, ventral view. Scale: 1mm.

FIGURES 26–29. Males of Ostrovus mitsukonis. 26. Terminalia, lateral view. Roman numerals indicate abdominal segments. vl = ventral lobe. 27. Terminalia, dorsal view. 28. Tergum 9, dorsal view. 29. Right paraproct, right lateral view. Scales: 1 mm (Figs. 26–28); 0.5 mm (Fig. 29).

FIGURES 37–41. Males of Ostrovus nikkoensis. 37. Terminalia, lateral view. vl = ventral lobe. 38. Terminalia, dorsal view. 39. Projection on the tergum 9, dorsal view. 40. Tergum 9, dorsal view. 41. Right paraproct, right lateral view. Scales: a = 1mm for Figs. 37–40; b = 0.5 mm for Fig. 41.

FIGURES 30–33. Variations of projections on the male tergum 9 in Ostrovus mitsukonis. 30. Kanagawa Pref., Honshu. 31. Kyoto City, Honshu. 32. Kochi Prefecture, Shikoku. 33. Miyazaki Prefecture, Kyushu. Scales: a = 1mm for Figs. 30, 31 and 33; b = 0.5 mm for Fig. 32.

FIGURES 35–36. Females of Ostrovus mitsukonis. 35. Terminalia, ventral view. 36. Variations of subgenital plates, ventral view. With a shallow midline concave collected from Kyoto City, Honshu (upper), and with two shallow concaves from Kochi Prefecture, Shikoku. Scales: 1mm.