Proguithera kiinugama

Ishikawa, Tadashi & Naka, Takeru, 2016, First record of the thread-legged assassin bug genus Proguithera from Japan, with description of a new species (Hemiptera: Heteroptera: Reduviidae), Zootaxa 4184 (1), pp. 184-192 : 185-190

Proguithera kiinugama Ishikawa & Naka, sp. nov.

( Figs. 1–36 )

Diagnosis. Among the species of Proguithera , this assassin bug is recognized by the following combination of morphological characters: body about 9 mm in length from apex of head to apex of forewing; anterior pronotal lobe lacking median longitudinal sulcus ( Fig. 5 ); cross vein connecting M+Cu vein and submarginal vein basad of discal cell incomplete ( Fig. 14 ); anteroventral and posteroventral series of profemur consisting of about 30 and 55 spinelike setae, respectively ( Fig. 15 ); struts of phallus exceeding apex of phallosoma in repose by about one-sixth of its length and visible from the outside of pygophore ( Figs. 20–23 , 27–28, 31–32 ).

Description. Male (holotype). Coloration. Body generally brownish yellow to yellowish brown ( Figs. 1–2 ). Head ( Figs. 7–8 ) darkened on posterior lobe; antenniferous tubercles, mandibular and maxillary plates, and labrum pale. Antenna dark brown; segment I brownish yellow on extreme base. Labial segments II and III yellowish brown; segment IV brownish yellow ( Fig. 8 ). Pronotum ( Figs. 5–6 ) darkened on tubercle of each anterolateral angle, on midline of posterior lobe, and on both sides of posterior half of posterior lobe. Scutellum and metascutellum darkened. Forewings ( Figs. 2 , 14 ) obscure, generally yellowish brown. Foreleg brownish yellow; coxa yellowish brown except venter; femur darkened on basal and apical parts and dorsum ( Figs. 1 , 15–16 ). Mid and hindlegs ( Fig. 1 ) dark brown; coxae and trochanters brownish yellow; tibiae becoming paler apicad; tarsi yellowish. Abdomen laterally suffused with reddish brown; posterior half of pygophore darkened ( Figs. 20, 22– 23 ).

Structure. Body covered with tiny granulations and with fine, decumbent setae. Head ( Figs. 7–8 ) about 1.25 times as long as width across eyes; anteoculus 1.6 times as long as postoculus, 1.4 times as long as length of eye in lateral view. Interocular space ( Fig. 7 ) about 1.8 times as wide as eye in dorsal view. Eye well projected laterad, elliptical in lateral view, not reaching dorsal and ventral outlines of head in lateral view. Antenna covered with fine, decumbent setae, about 1.4 times as long as body length (to apex of forewing); approximate proportion of segments I to IV 10: 7: 2.7: 3.6. Labium ( Fig. 8 ) sparsely covered with fine setae; approximate proportion of segments II to IV 1: 1.2: 1.6.

Pronotum ( Figs. 5–6 ) along midline about 1.2 times as long as head, about 1.2 times as long as humeral width, divided vaguely into anterior and posterior lobes at middle, roundly tumid on each anterolateral angle, with largely concave posterior margin; anterior lobe convex on disc, lacking median longitudinal sulcus; posterior lobe weakly rugose, about 0.6 times as long as humeral width. Forewings exceeding apex of abdomen by about one-ninth of its length ( Fig. 1 ); cross vein connecting M+Cu vein and submarginal vein basad of discal cell ( Fig. 14 ) incomplete; Rs vein rudimentary and barely noticeable. Foreleg covered with fine, decumbent setae; coxa 1.2 times as long as pronotum, 5.3 times as long as its maximum width; femur ( Figs. 15–16 ) 1.6 times as long as coxa, about 6 times as long as its maximum width, with anteroventral and posteroventral series of spine-like setae inserted on low tubercles; anteroventral series ( Figs. 15–16 ) composed of about 30 spine-like setae, beginning at basal third of femur, with basalmost setae longest among setae of anteroventral series; posteroventral series composed of about 55 spine-like setae, with basal fifth or sixth seta longest among setae of posteroventral series; spine-like setae of both series uniform in shape, various in length but shorter than maximum width of femur. Tibia ( Figs. 17–18 ) slightly less than half as long as profemur, with a ventral row composed of about 17 short, deflexed and spine-like setae along apical three-fifths of tibia; tarsus ( Fig. 19 ) 0.9 times as long as protibia; approximate proportion of tarsal segments I to II 5.5:1. Mid and hindlegs ( Figs. 1–2 ) slender, covered with fine setae; mesofemur as long as antennal segment I; mesotibia 1.4 times as long as mesofemur; metafemur as long as mesotibia; metatibia 1.5 times as long as metafemur.

Abdomen covered with fine decumbent setae, weakly widened posteriad, 3.3 times as long as its maximum width. Pygophore ( Figs. 20–23 , 27–28 ) covered with setae in posterior half, about twice as long as its maximum width, about 1.6 times as long as its maximum height, with a rounded posterior margin. Paramere ( Figs. 29–30 ) rod-shaped, slightly curved in apical third, rounded at apex, covered with setae in apical half; these setae shorter than width of paramere. Phallus ( Figs. 31–32 ) elongated-oblong, nearly cylindrical, ventrally with narrow sclerotized stripe along meson over entire length of phallosoma; basal plate ( Fig. 33 ) strong, with narrow and short basal plate bridge; dorsal phallothecal sclerite wide, weakly sclerotized; struts ( Figs. 31–32 ) slender, gradually tapered, acute at apex, exceeding apex of phallosoma in repose by about one-sixth of its length; apical part of struts visible from outside of pygophore ( Figs. 20–23 , 27–28 ); 1+1 lateral group of endosoma composed of a number of minute triangular sclerites ( Fig. 31 ).

Female. Almost the same as male in general appearance ( Figs. 3–4 , 11–13 ). Eyes somewhat smaller than those of male ( Figs. 9–10 ). Valvifer I ( Figs. 24–26 , 34 ) darkened in lower half, oblong, covered with short setae in apical half, and with straight posterior margin. Valvula I ( Figs. 24–26 , 34 ) nearly triangular, rounded at apex, covered with short to long setae. Styloides ( Fig. 24–26 , 35 ) separated from each other, covered with short to long setae in apical half, rounded at apex in dorsal view, with small triangular projection apicoventrally.

Measurements [in mm, ♂ (n = 1, holotype) / ♀ (n = 3)]. Body length (from apex of head to apex of abdomen, from apex of head to apex of forewing) 8.70, 9.40 / 8.60–8.80, 8.90–9.30. Head length 1.28 / 1.22–1.24, width across eyes 1.03 / 0.83–0.85; interocular space 0.44 / 0.44; length of anteoculus 0.53 / 0.55–0.57, of postoculus 0.33 / 0.30–0.36; antenna length 12.85 / 11.75–12.25, lengths of antennal segments I 5.50 / 4.90–5.10, II 3.90 / 3.60–3.70, III 1.48 / 1.42–1.54, and IV 1.97 / 1.80–1.92; labium length 1.46 / 1.42–1.47, lengths of labial segments II 0.38 / 0.35–0.37, III 0.46 / 0.45–0.46, and IV 0.62 / 0.61–0.65. Length of pronotum 1.51 / 1.53–1.57; width across humeri 1.28 / 1.22–1.30. Forewing length 6.3 / 6.2–6.3. Lengths of foreleg femur 3.01 / 2.96–3.01, tibia 1.42 / 1.39–1.43, and tarsus 1.27 / 1.28–1.32; of midleg femur 5.40 / 5.20–5.30, tibia 7.50 / 7.10–7.30, and tarsus 0.35 / 0.35; of hindleg femur 7.20 / 6.80–7.10, tibia 10.90 / 10.40–10.70, and tarsus 0.38 / 0.37–0.39. Abdomen length 4.40 / 4.40–4.50.

Type series. Holotype: ♂ ( Figs. 1–2 , 5–8 , 14–23 , 27–33 ), “ JAPAN The Ryukyus, Ishigaki-jima Is., Mt. Yarabu-dake, 24.44165N 124.09044E, 23. V. 2016, Takeru Naka ” . Paratypes (n = 3): 1 ♀ ( Figs. 9–13 , 24–26 ), same data as holotype ; 2 ♀♀ (1 ♀ for Figs. 3–4 , 34–35 ), same locality and collector, 24.44150N 124.08975E, 17.vi.2015. All type materials are preserved in the Laboratory of Entomology , Faculty of Agriculture , Tokyo University of Agriculture.

Distribution. Japan: Ryukyu Islands (Ishigaki-jima Island).

Etymology. The specific epithet is named after a Ryukyuan dialect “ kiinugama ” (= a tree hollow), referring to the habitat of the new species; a noun in apposition.

Generic placement. Wygodzinsky (1966) recognized three subgenera in the genus Guithera Distant, 1906, each containing a single species: Lutevula Breddin, 1909, Proguithera Wygodzinsky, 1966 , and the nominotypical Guithera. Subsequently, Villiers (1970) and Dispons (1970) upgraded Lutevula and Proguithera to the generic rank, respectively. Although these three genera are currently regard as distinct, the species of the genera are undoubtedly closely related to each other, as stated by Rédei (2004), who treated these taxa as the Guithera- Lutevula group. One of the important distinctions between the genera is the number of the segments of the protarsi; on that basis, this new species with two-segmented protarsi evidently would belong to Proguithera . The genus Proguithera therefore consists of three species now, Proguithera drescheri , P. inexpectata , and P. kiinugama sp. nov. The discovery of this new species, however, demonstrates that there is an inconsistency in the morphological characters that define Proguithera . Although Wygodzinsky (1966) stated that Proguithera possesses the Rs vein and a cross vein connecting the M+Cu vein and a submarginal vein basad of the discal cell on the forewings, the new species has a rudimentary Rs vein ( Fig. 11 ) and an incomplete cross vein ( Figs. 12–14 ), which are conditions similar to those of the genus Guithera. It may be necessary to revise the generic divisions and definitions in the Guithera-Lutevula group; however, we postpone any final conclusion about these divisions and definitions until more specimens and/or species belonging to the group become available for study.

Comparative notes. Among the previously known species of the Guithera-Lutevula group, as mentioned above, P. kiinugama sp. nov. resembles P. drescheri and P. inexpectata in general appearance as well as in having two-segmented protarsi. However, the new species may be distinguished from G. drescheri based on the following characters: median longitudinal sulcus on the anterior pronotal lobe absent ( Fig. 5 ) (in P. drescheri , the sulcus is present); forewing with an incomplete cross vein connecting the M+Cu vein and a submarginal vein basad of the discal cell ( Figs. 12–14 ) (vs. vein complete); Rs vein of the forewings rudimentary and barely noticeable ( Fig. 11 ) (vs. Rs vein clear); anteroventral series of the profemur consisting of about 30 spine-like setae ( Fig. 15 ) (vs. consisting of not more than 20 spine-like setae); and posteroventral series of the profemur consisting of about 55 spine-like setae ( Fig. 15 ) (vs. consisting of about 45 spine-like setae). Moreover, the new species is separable from P. inexpectata in the following ways: body size smaller (approximately 9 mm in length from apex of head to apex of forewing) (in P. inexpectata , 11.5 mm); median longitudinal sulcus on the anterior pronotal lobe absent ( Fig. 5 ) (vs. the sulcus is finely present); forewing with an incomplete cross vein connecting the M+Cu vein and a submarginal vein basad of the discal cell ( Figs. 12–14 ) (vs. vein complete); anteroventral series of the profemur consisting of about 30 spine-like setae ( Fig. 15 ) (vs. consisting of about 40 spine-like setae); and posteroventral series of the profemur consisting of about 55 spine-like setae ( Fig. 15 ) (vs. consisting of 65–70 spine-like setae).

Biological notes. All the specimens examined here (four individuals) were collected from Mt. Yarabu-dake on Ishigaki-jima Island in the Ryukyu Islands, a locality that belongs to the subtropical zone. Mt. Yarabu-dake has well preserved forests, including a number of large trees, but the forests are relatively dry ( Fig. 38 ). All the individual specimens were found at night and were standing still or walking very slowly on the inside walls of hollows developed in large trees, especially Castanopsis sieboldii (Makino) Hatusima (Fagaceae) that were 65 to 180 cm in diameter at breast height ( Figs. 36–37, 39 ). When presented with a stimulus, the assassin bugs escaped with rapid walking to a gap between the hollow and the tree bark. In microenvironments similar to the ones where the assassin bugs were found, harvestmen, or Opiliones, were frequently observed; however, these two groups have not yet been seen simultaneously.

Figures

FIGURES 1 – 4. Proguithera kiinugama sp. nov., male (1 – 2) and female (3 – 4), lateral (1, 3) and dorsal (2, 4) views. Scale bar: 5 mm.

FIGURES 5 – 10. Proguithera kiinugama sp. nov. 5 – 6, Head and prothorax, male, dorsal (5) and lateral (6) views; 7 – 10, head, male (7 – 8) and female (9 – 10), dorsal (7, 9) and lateral (8, 10) views. Scale bar: 0.5 mm.

FIGURES 11 – 14. Forewing of Proguithera kiinugama sp. nov., male (14) and female (11 – 13). 11, Habitus of right wing; 12 – 14, basal part of discal cell and its adjacent area, right (12) and left (13 – 14) wing. Black arrows each indicating an incomplete cross vein connecting the M + Cu vein and a submarginal vein basad of the discal cell; a white arrow indicating a rudimentary Rs vein. Abbreviations: dc, discal cell. Scale bar: 1.0 mm for Fig. 11; 0.2 mm for Figs. 12 – 14.

FIGURES 15 – 19. Left foreleg of Proguithera kiinugama sp. nov., male. 15, Femur, anterolateral view; 16 basal part of femur, anterolateral view; 17 – 18, tibia, anterolateral (17) and ventral (18) views; 19, tarsus, anterolateral view. Scale bar: 1.0 mm for Fig. 15; 0.5 mm for Figs. 16 – 19.

FIGURES 20 – 26. Apical part of abdomen of Proguithera kiinugama sp. nov., male (20 – 23) and female (24 – 26), lateral (20, 24), dorsal (21), posteroventral (22, 26), ventral (25), and posterior (23) views. Abbreviations: str, apical part of struts of phallus; sty, styloides; t 9, tergite IX; va 1, valvula I; vf 1, valvifer I. Scale bar: 0.5 mm.

FIGURES 27 – 35. Genitalia of Proguithera kiinugama sp. nov., male (27 – 33) and female (34 – 35). 27 – 28, Pygophore, lateral (27) and dorsal (28) views; 29 – 30, left paramere, lateral (29) and dorsal (30) views; 31 – 32, phallus, lateral (31) and dorsal (32) views; 33, basal plate, dorsal view; 34, right valvifer I and valvula I, ventral view; 35, styloides, dorsal view. Abbreviations: str, struts of phallus; va 1, valvula I; vf 1, valvifer I. Scale bar: 0.2 mm.

FIGURES 36 – 39. Habitats of Proguithera kiinugama sp. nov. 36, A living specimen on the inside wall of a hollow developed within a large Castanopsis sieboldii; 37, the basal part (including the hollow) of the tree shown in Fig. 36; 38, a forest on Mt. Yarabu-dake with large trees; 39, another hollow in which P. kiinugama sp. nov. was found.