Malthinus serrulatus N. Takahashi, sp. nov.

Malthinus serrulatus N. Takahashi, sp. nov.

(Japanese name: Amami-kurosuji-tsumaki-joukai) (Figs. 5–6, 28–36)

Description. MALE. Almost similar to M. mucoreus in general appearance. Body chiefly reddish yellow to orangish yellow with palish yellow apical portions of elytra and some dark-coloured parts; maxillary and labial palpi, basal parts of antennae, lateral areas of pronotum, legs, and sometimes metaventrite except for lateral areas faintly darker; antennae except for basal few segments sometimes brownish; eyes black; vertexal marking on head, medio-longitudinal area of pronotum, scutellum, elytron except for basal and mesal areas and ventral margin of epipleuron brownish black, but somewhat more brownish on scutellum and more grayish on blackish area of each elytron; vertexal marking on head somewhat obovate in shape, extended to posterior end of head, and slightly blurred on the border; apical halves of mandibles, tibial spurs, and tarsal claws reddish brown; 4th tarsal segments and rarely the adjacent parts dark brownish; venter except for last two or three segments and lateral areas on each abdominal sternite sometimes dusky.

Head somewhat broader than long, 1.51 (in the holotype; range 1.46–1.58) times as wide as pronotum, gently convex dorsad, faintly furrowed medio-longitudinally around the middle of posterior margin which is often hidden under the anterior margin of pronotum, somewhat flattened before vertex, weakly swollen mesad around antennal pits, feebly depressed apicad just before antennal sockets, gently arcuate at apical margin of clypeus; surface puncticulate and lustrous before antennal pits, rugulose in posterior area but slightly smoother before vertex, finely granulate and matt on ventral side though almost impunctate and lustrous on stipes of maxillary palpi; eyes medium in size, semiglobular and protrudent laterad, interocular distance 3.21 (3.21–3.85) times as large as radius of eye; antennae filiform, reaching about basal 7/9 of elytra, 1st segment subclavate, 2nd somewhat subclavate, 3rd to 11th subcylindrical, and relative lengths of antennal segments from base as follows—19.2: 11.1: 11.8: 14.2: 14.5: 14.9: 13.5: 12.8: 11.1: 10.5: 11.5.

Pronotum subquadrate, 1.00 (0.97–1.09) times as long as wide; disc mostly granulate but slightly rugulose on blackish marking, convex medio-dorsad, transversely and weakly swollen from side to side at middle, somewhat elevated in medio-basal area though slightly hollowed in the middle, subtruncate to faintly arcuate at anterior margin, obliquely narrowed apicad at front angles, obtusely rounded at hind angles, gently arcuate posteriad but shallowly emarginate in the middle and feebly marginate at posterior margin; lateral margins subparallel behind front angles, faintly and roundly protruded laterad at middle, and shallowly emarginate mesad before hind angles. Scutellum subtrapezoidal and narrowed posteriad, covered with fine pubescence.

Elytra 2.60 (2.60–2.95) times as long as wide; each surface rugulose but smoother around humerus and apex, feebly marginate along the suture, bearing a few vague costae, weakly and longitudinally punctate in rows, particularly so in mesal area, the punctures becoming indistinct distad in other area. Legs moderately slender and simple; all claws simple; relative lengths of metatarsal segments from base as follows—16.3: 8.1: 5.2: 7.0: 7.3.

Meso- and metaventrites puncticulate and lustrous on their surfaces. Venter other than 9th abdominal sternite relatively smooth and lustrous though somewhat rugulose, and each sternite except for last two segments sometimes matt along posterior margin; 8th sternite widely, roundly but somewhat trapezoidally emarginate at posterior margin; 9th relatively thin, arcuate along ventral surface of basal piece of genitalia in profile, mostly granulate and matt on surface in ventral view, though relatively smooth in basal area along penultimate margin, broad at base, narrowed apicad at sides in basal half, slender and subparallel in apical half, subtruncate to bilobed as in M. mucoreus at apex.

Male genitalia generally as in M. mucoreus; ventral part of basal piece somewhat deeply incised in the middle at apical margin in caudal view; dorsal part of basal piece gently convex medio-dorsad though flattened in mesal area except for base in basal half; lateral lobe faintly sinuate in outline and laterally compressed in apical part in dorsal view, transverse elliptical with serrulate margin around apex and acutely projected at latero-basal part in profile, with a longitudinal row of small spines on apical two-thirds of dorsum, which are sometimes partly obsolete.

Length of body: 3.8 (3.4–4.2) mm; width of body: 0.9 (0.8–1.0) mm; length of hind tibia: 1.3 (1.0–1.4) mm.

FEMALE. Similar to male, but body slightly larger and darker in coloration, sometimes having larger blackish parts than in male; vertexal marking often larger and extending over the posterior area behind eyes on dorsum of head except for tempora; penultimate abdominal sternite sometimes dusky in antero-central area. Head 1.35–1.42 times as wide as pronotum; eyes smaller than in male and interocular distance 4.03–4.62 times as large as radius of eye; antennae shorter than in male, reaching about basal 4/7 of elytra, and relative lengths of antennal segments from base as follows—21.3: 12.3: 12.3: 13.6: 14.3: 14.3: 13.6: 12.3: 11.5: 10.6: 11.2. Pronotum 1.00–1.10 times as long as wide. Elytra 2.48–2.75 times as long as wide. Relative lengths of metatarsal segments from base as follows—15.8: 8.8: 5.6: 7.5: 8.5. Eighth abdominal sternite as in M.

mucoreus. Female terminalia somewhat stout; paraproct almost divided symmetrically into two parts, each part somewhat ovate in outline but not constricted basad in apical part in dorso-lateral view; coxite subcylindrical though slightly flattened dorso-ventrad, gently curved mesad, subtruncate at apex in ventral view, with a lapel at the base which is tapered at the mesal part.

Length of body: 4.2–4.8 mm; width of body: 1.0– 1.2 mm; length of hind tibia: 1.0– 1.5 mm.

Type series. Holotype (Type No.3310, ELKU), male, Kinsakubaru, Amami-Ôshima Is., Kagoshima Pref., 1.iv.1995, R. Matsumoto leg. Paratypes, RYUKYUS (Amami-Ôshima Is.) Same data as holotype, 1 female (ELKU). Same locality as holotype, 1 male, 2.iv.1995, R. Matsumoto leg. (ELKU); 1 male, 2.v.1996, R. Matsumoto leg. (NTC). Shinmura–Yuwan, 1 male, 4.iv.1956, S. Miyamoto leg. (ELKU). Yuwan, 1 male, 7– 9.iv.1956, S. Miyamoto leg. (ELKU). Chûô-rindô, 1 female, 18.iii.1991, H. Kojima leg.; 2 females, 2.iv.1993, H. Yoshitomi leg. Mt. Yuwan, 1 male and 4 females, 1.iv.1993, H. Yoshitomi leg.; 1 female, 29.iii.1995, R. Matsumoto leg.; 1 male and 1 female, 5.iv.1995, R. Matsumoto leg.; 2 males and 4 females, 23.iv.1995, N. Takahashi leg.; 1 female, 24.iv.1995, N. Takahashi leg.; 1 male and 3 females, 25.iv.1995, N. Takahashi leg. Mt. Yuwan (by light trap), 1 female, 24.iv.1995, N. Takahashi leg. Mt. Yui, 1 male and 1 female, 30.iii.1995, T. Yamauchi leg.; 2 females, 31.iii.1995, R. Matsumoto leg.; 1 female, 24.iv.1995, N. Takahashi leg.; 5 males, 28.iv.2006, N. Takahashi leg. Mt. Rankan, 5 males and 2 females, 2.iv.1995, R. Matsumoto leg.; 2 males, 4.iv.1995, R. Matsumoto leg. Akakina, 5 males and 6 females, 4.iv.1995, R. Matsumoto leg. Naze City, Asato, 1 male and 2 females, 21.iv.1997, N. Takahashi leg. Naze, Asato Pass, 1 female, 30.iv.2006, N. Takahashi leg. Naze–Tatsugou, Honcha Pass, 1 male and 2 females, 1.v.2006, N. Takahashi leg. Mt. Akatsuchi, 1 female, 26.iii.1996, M. Satô leg. (MSC). No detailed locality name, 1 female, iv.1954, T. Kumata, T. Oku & S. Takagi leg. (SEHU). (Tokunoshima Is.) Kametoku, 3 males and 3 females, 6.iv.1968, M. Tomokuni leg. (MSC); 1 male, 7.iv.1968, M. Tomokuni leg. (MSC). Mt. Inokawa, 3 males, 28.iv.1996, R. Matsumoto leg.

Distribution. Japan: middle Ryukyus (Amami-Ôshima Is. and Tokunoshima Is.).

Infraspecific variation. Infraspecific variations are recognized in some parts and some morphological characters are not distinctly stable in particular areas. The vertexal marking on the head is variable in shape and size, obovate to oblong or obtrapezoidal in male, rarely reduced into a transverse elliptical or obcordate in shape and often extended over a large part posterior to the vertex on the dorsum in female. The apex of the male 9th abdominal sternite also varies in shape from subtruncate to bilobate. Most of the female elytron is sometimes dusky except for the yellowish apical spot, although small yellowish parts remain only at the basal area and along the suture and ventral margin of the epipleuron. Lateral lobe of the male genitalia is smooth at the dorsal margin of the apical part in material collected from Tokunoshima Island.

Remarks. This new species is closely related to M. mucoreus, but can be distinguished from the latter by the somewhat evener pronotum, the often larger vertexal marking on the female head, the elliptical apex with serrulate margin of the lateral lobe and the more basally located acute projection at the latero-basal part in the male genitalia, and the gently curved coxites with subtruncate apices in the female terminalia.

Notes. The soldier beetles, identified as “ Malthinus okinawanus ” in Kato (2000) and regarded as “ Malthinus mucoreus ” after being collected on Amami-Ôshima Island by Kiriyama & Kinoda (2000), may possibly belong to this new species.

Etymology. Derived from Latin serrula = small saw; the specific epithet refers to the serrulate apical part of the lateral lobe in the male genitalia.