Plethus ukalegon Malicky and Chantaramongkol

Ito, Tomiko & Saito, Rie, 2016, First record of Plethus Hagen (Trichoptera, Hydroptilidae) from Japan, with description of a species, Zootaxa 4154 (4), pp. 466-476 : 468-475

Plethus ukalegon Malicky and Chantaramongkol

( Figs 2–5 )

Plethus ukalegon Malicky and Chantaramongkol 2007, 1047 , 1092. Holotype male, Taiwan.

Adult ( Figs 2 , 3 A–3C). Antennae each 18-segmented, basal 4/5 black and apical 1/5 white. Spur formula 1-2-3; spurs of prothoracic legs very small, 0.03 mm long, but visible at high magnification.

Male ( Fig. 2 ). Lengths of forewings, hind wings, and antennae 1.3–1.5 mm, 1.0– 1.3 mm, and 0.4–0.5 mm, respectively (n = 5).

Genitalia ( Figs 2 D–2H). Segment IX subquadrate with long anteroventral apodemes (‘stems’ in Malicky & Chantaramongkol 2007), apodemes slightly longer than segment; dorsally subquadrate with anterior margin slightly concave, posterior margin broadly concave in dorsal view; ventrally subquadrate with anterior margin slightly concave and posterior margin incised between inferior appendages in ventral view. Dorsal plate semimembranous, slightly sclerotized laterally in dorsal view. Inferior appendages short, setose, subquadrate in lateral and ventral views. Phallus long, about 3 times as long as segment IX, with median long straight spine and 4–5 pairs of short spines subapically, some of these short spines curved.

Female ( Figs 3 A–3C). Lengths of forewings, hind wings, and antennae 1.5–1.7 mm, 1.1–1.4 mm, and 0.4–0.5 mm, respectively (n = 5).

Abdominal segments I–VII densely covered with long thick setae. Tergite and sternite VIII fused laterally forming tubular segment. Segment VIII almost as long as segment VII, often withdrawn into segment VII, slightly sclerotized in apical 1/4 with 5 pairs of marginal setae. Bursa complex heavily sclerotized with round opening, apical half bell-shaped in ventral view.

Pupa ( Figs 3 D–3F). Somewhat depressed, flattened dorsoventrally, length up to 1.7 mm, milky white. Mandibles very sharp, inner blades without teeth. Antennae and wing pads almost reaching to mesothorax and abdominal segment VIII, respectively. Hook plates on abdominal segments III–VI; ellipsoidal hook plates near posterior margins of segments III–VI; small round hook plates at middle of segments V–VI; hook plates with 30– 40 fine hooks each. Lateral fringes absent.

Larva. Final instar larva ( Fig. 4 ). Body somewhat depressed, flattened dorsoventrally, length up to 1.7 mm, sclerotized parts black or deep brown, others milky white.

Head. Dark brown, near trapezoidal, width about 0.31 mm, length slightly longer than width; with dark Yshaped ecdysial lines posteriorly but frontoclypeal lines incomplete anteriorly; longest setae (setae no. 9, sensu Wiggins 1996) slightly longer than head width. Antennae situated near anterior edge of head capsule, each unsegmented with short round sensilla apically. Mandibles stout, each with blunt apex and blunt subapicomesal tooth, mesal brushes not visible. Labrum sclerotized in basal 2/3, otherwise semi-membranous, brushes of setae not visible or absent at anterior margin.

Thorax. Dorsum of each segment covered with pair of large square nota; plates dark brown, meso- and metanota with black anterolateral corners; each plate bearing 25–30 setae; 1 long seta on each anterolateral corner, other setae short. Pair of transverse rectangular sclerites posteriorly on prosternum about 6 times as wide as long, absent on meso- and metasterna. Thoracic legs short and stout; structures similar in all 3 legs; tibial spurs single, subacute apically. Foretrochantin rectangular with irregularly protruded margin, pleuron of mesothorax rectangular, and pleuron of metathorax ellipsoidal.

Abdomen. Somewhat flattened dorso-ventrally, segments III–VI slightly expanded. Tracheal gills, humps, lateral fringes, lateral tubercles and chloride epithelia absent. Segments I–VIII each with 1 long and 1 short seta directed laterad from mid lateral margin. Dorsal sclerites conspicuous on segments I–VII. Tergum I, with transverse anteromedian sclerite about 3 times as wide as long and bearing pair of submedian setae, pair of small round sclerites near anterolateral corners each with single seta, and pair of transverse sclerites near posterior margin. On terga II–VII, anteromedian sclerites each about 4.5 times as wide as long with 4, rarely 5, light spots (chloride epithelia, sensu Wells & Huisman, 1993); posteromedian rectangular sclerites each about 7 times as wide as long and with pair of sublateral setae, pair of small oval seta-bearing sclerites near anterolateral corners, and pair of transverse sclerites near posterior margin. Posteromedian dorsal sclerite of tergum VIII ellipsoidal, about 3 times as wide a long, with 3 pairs of long and 2 pairs of short setae. Dorsal sclerite of tergum IX semicircular with 3 pairs of long and 2 pairs of short setae. Lateral sclerites of segment X rectangular with 2 pairs of long and 3 pairs of short setae. Anal claws directed anterolaterad, without accessory hooks.

Early instar larva ( Fig. 5 ). Body cylindrical, slightly depressed dorsoventrally, brown, with many long and short setae on thorax and abdomen, length up to 1.2 mm in larva.

Head. Nearly trapezoidal, width 0.22 mm in pre-final instar; dorsal ecdysial lines distinct, longest setae (setae no. 9, sensu Wiggins 1996) nearly 1.3 times head width, antennae arising near anterolateral corners of head capsule, each with fine seta subapically.

Thorax. Dorsal plates of 3 thoracic segments rectangular, without dorsal ecdysial lines, prothorax narrowest and metathorax widest, with several pairs of long setae and many short setae lining anterior edges and across middle. Thoracic legs short and stout; structures of 3 legs similar; tibiae each with 2 subapical, acute spurs.

Abdomen. Dorsal plates on segments I–VIII widely trapezoidal, each with pair of long posterolateral setae shorter than body width, other setae near posterolateral corners, 3 pairs of short setae near posterior margins, and many short setae and spines on lateral and posterior margins. Dorsal plate of segment IX semicircular, with 4 pairs of long, posterior-margin setae shorter than body width, several short setae dorsally. Anal legs curved, without accessary hooks.

Case ( Figs 3 G– 3I, 6E, 6F). Case of final instar larva made of silk, comprising ventral and dorsal valves; ventral valves represented by flat sheets with longitudinal median groove and transverse lateral fluting; dorsal valves forming convex dome, rarely carried tortoise-like, larger than ventral valve and with prominent anterior and posterior hoods concealing the larva completely, hoods with radical flares; length ≤ 2 mm; almost always attached tightly on rocks. Anterior and posterior edges of cases fixed to substrate before pupation, with more or less reduced anterior and posterior hoods.

Specimens examined. Japan, Ryukyu Islands , Iriomote-jima : Urauchi-gawa, uppermost part of Kampireno-taki: 1 male, 9 females, 5.xii.1991, R.B. Kuranishi (deposited in personal collection of R.B. Kuranishi) ; 14 pupae, 179 larvae, 25.iii.1999, TI; 17 males, 6 females, 14.iv.2005, TI; 197 males, 127 females, 29.x.2012, TI; 5 males, 9 females, 30.xi.2013, TI & RS; 4 males, 4 females, 48 pupae, 5 prepupae, 1140 final instar larvae, 8 early instar larvae, 22.x.2015, TI & RS; 77 males, 193 females, 12 pupae, 12 prepupae, 1258 final instar larvae, 153 early instar larvae, 23.iii.2016, TI. Omija-gawa, Omija-bashi: 37 males, 13 females, 34 pupae, 9 prepupae, 38 final instar larvae, 24.iii.1999, TI; 4 males, 4 females, 5 pupae, 4 prepupae, 24 final instar larvae, 13.iv.2005, TI; 20 males, 1 female, 30.xi.2013, TI & RS; 4 males, 1 female, 21–22.x.2015, TI & RS; 59 males, 26 females, 1 pupa, 28 final instar larvae, 22.iii.2016, TI. 2 males, 1 female, Omija-gawa , a fall, 22.iii.2016, TI. Nishifunatsuki-gawa, Nishifunatsuki-bashi : 15 males, 16 females, 21.iii.1996, H. Nishimoto; 21 pupae, 1 prepupa, 13 final instar larvae, 23.iii.1999, TI; 16 males, 30 females, 30.x.2010, TI; 1 female, 28.xi.2013, TI & RS; 27 males, 25 females, 21.iii.2016, TI. Yuchin-gawa, Mayarokku-no-taki: 7 males, 2 females, 23.x.2015, TI & RS; 19 males, 9 females, 22.iii.2016, TI. 59 males, 25 females, Aira-gawa , middle reach, 21.iii.2016, TI . 3 males, 7 females, Yukishidagawa , hygropetric zone, 13.iv.2005, TI. Ishigaki-jima: Miyara-gawa, Maezato-damu-ue : 14 males, 13 females, 12.iv.2012, TI; 74 males, 26 females, 20.iii.2016, TI. Fukidori-gawa, middle reach: 24 males, 15 females, 26.xi.2013, TI & RS; 43 males, 6 females, 20.iii.2016, TI. Nagura, Shiramizu, hygropetric zone: 1 female, 12.iv.2011, TI; 2 males, 4 females, 27.xi.2013, TI & RS. 21 males, 40 females, Nagura-gawa , middle reach, 18.iii.2016, TI . 1 male, 1 female, a fall beside foot path of Mt. Omoto-dake , 20.iii.2016, TI.

Remarks. The male of Plethus ukalegon is characterized by the subquadrate segment IX, subquadrate inferior appendages, and a long spine and a few pairs of short spines on the phallus ( Malicky & Chantaramongkol 2007). Specimens taken on the southern Ryukyu Islands differ slightly from the Taiwanese holotype male as follows: The anterior apodemes of segment IX are slightly longer than the segment in Ryukyu Island specimens (shorter than segment IX in the Taiwanese specimen), inferior appendages are directed ventrocaudad in Ryukyu Island specimens (directed dorsocaudad in the Taiwanese male). However, Hans Malicky (personal communication, 26 December 2015) wrote to us as follows: “In Taiwanese, anterior apodemes of segment IX are variable in length individually and inferior appendages direct ventro-caudad or dorso-caudad, depending on observation angles.” Therefore, we accept that the Japanese specimens are referable to the Taiwanese species, P. ukalegon .

Distribution ( Fig. 6 A). Taiwan, Japan (Ryukyu Islands: Iriomote-jima, Ishigaki-jima). New to Japan.

Habitat ( Figs 6 B–6E). Larvae and pupae of this species live on smooth rock surfaces in fast-flowing waters such as hygropetric zones, rapid streams, and waterfalls. They are sometimes abundant on the smooth rock surfaces. For example, we observed a high density of larvae and pupae (22.0 ± 9.0 / 100 cm 2; average ± SD, n=60) in our quantitative surveys at the uppermost part of Kampire-no-taki, Iriomote-jima (water current 40–120 cm / second, water depth 1–5 mm) on 22 October 2015. Many larvae of microcaddisflies ( Stactobia sp.) and mayflies ( Baetidae ) and a few larvae of stoneflies, blackflies, and non-biting midges were collected together. The adults were caught by sweep netting, not trapped at light despite attempts to capture specimens in this way.

Japanese name. Gamban-himetobikera-zoku. Gamban-himetobikera (newly created here).

Figures

FIGURE 2. Plethus ukalegon Malicky and Chantaramongkol 2007 male. 2 A, head and thorax, dorsal; 2 B, spurs of 3 thoracic legs; 2 C, right wings, dorsal; 2 D, genitalia, left lateral; 2 E, same, dorsal; 2 F, same, ventral; 2 G, phallus, dorsal; 2 H, same, variation. Abbreviations: IX = abdominal segment IX; dp = dorsal plate; ia = inferior appendage; ph = phallus.

FIGURE 3. Plethus ukalegon Malicky and Chantaramongkol 2007 female, pupa, and case. 3 A – 3 C, female: 3 A, abdominal segments VII – X, left lateral; 3 B, abdominal segments VIII – X, dorsal; 3 C, same, ventral. 3 D – 3 F, pupa: 3 D, habitus, dorsal; 3 E, right mandible, dorsal; 3 F, hook plate near posterior edge of abdominal segment V, dorsal. 3 G – 3 I, case: 3 G, case of pupa, dorsal; 3 H, case of larva, ventral; 3 I, same, dorsal. Abbreviations: VII – X = abdominal segments VII – X.

FIGURE 4. Plethus ukalegon Malicky and Chantaramongkol 2007 final instar larva. 4 A, habitus, dorsal; 4 B, head, dorsal; 4 C, labrum, dorsal; 4 D, right mandible, dorsal; 4 E, left antenna, dorsal; 4 F, sclerites of prosternum, ventral; 4 G, right half of dorsal plate of mesothorax; 4 H, 3 thoracic legs and pleura; 4 I, abdominal segment I, dorsal; 4 J, abdominal segment III, dorsal; 4 K, posterior parts of abdomen, dorsal.

FIGURE 5. Plethus ukalegon Malicky and Chantaramongkol 2007 early instar larva. 5 A, habitus, dorsal; 5 B, right antenna, dorsal; 5 C, right prothoracic leg, posterodorsal; 5 D, apical part of right prothoracic leg, posterodorsal; 5 E, abdominal segment IV, dorsal; 5 F, left anal proleg, dorsolateral.

FIGURE 6. Plethus ukalegon Malicky and Chantaramongkol 2007 distribution, 3 typical habitats, and case. 6 A, distribution shown by circles; 6 B, hygropetric zone on wet rock face (Shiramizu, Nagura, Ishigaki-jima, 27 November 2013); 6 C, fastflowing stream (Nagura-gawa, Ishigaki-jima, 18 March 2016); 6 D, waterfall (Kampire-no-taki, Iriomote-jima, 22 October 2015); 6 E, larval and pupal cases attached on rock surface (encircled; Kampire-no-taki, Iriomote-jima, 22 October 2015); 6 F, larva in its case, dorsal.