Myrmecolax arcuatus, Lu & Liu, 2014

Lu, Xiumei & Liu, Xingyue, 2014, Discovery of the twisted-wing parasite family Myrmecolacidae (Insecta: Strepsiptera) from China, with description of two new species of the genus Myrmecolax Westwood, 1861, Zootaxa 3881 (4), pp. 385-395 : 390-394

Myrmecolax arcuatus sp. nov.

( Figs. 4–6 )

Description. Male. Total body length 1.87 mm.

Head transversely wide, wider than metathorax; hypognathous; anterior part reddish brown, covered with dense hairs, median part creamy yellow, smooth in dorsal view; frons dark brown, anteriorly produced and noselike; gena pale brown, distinctly with brownish narrow band-like markings extending laterally between clypeus and gena; clypeus dark brown, covered with dense short hairs, slightly convex (length of head 289.24 µm, width 736.96 µm, width between compound eyes 312.38 µm).

Compound eye dark brown, semiglobular, extending to ventral side of head, composed of ~21 large ommatidia, which are widely separated with intervals densely covered by microtrichia in lateral and dorsal view; proximal ommatidia more closely neighbored to each other than median ones; ocellus absent; number of ommatidia 21±3.

Antenna 7-segmented, hanging ventrad; 1 st and 2 nd antennomeres short (length of 1 st antennomere 85.32 µm, length of 2 nd antennomere 31.44 µm); 1 st antennomere cup-shaped, slightly narrow at base (proximal width of 1 st antennomere 65.41 µm, distal width of 94.06 µm); 2 nd antennomere ring-like, shorter than 1 st antennomere; 3 rd antennomere with an extremely long, obtusely tipped, flabellum, which nearly reaches distal part of 7 th antennomere (length of 3 rd antennomere 57.10 µm); 4 th antennomere rather short, wider than long (length of 4 th antennomere 50.91 µm, width 64.84 µm); 5 th –7 th antennomeres long, gradually narrowed distad; 5 th antennomere nearly as long as 6 th plus 7 th antennomeres (length of 5 th antennomere 520.55 µm); 7 th antennomere slightly longer than 6 th antennomere, with an acutely pointed tip (length of 6 th antennomere 240.54 µm, length of 7 th antennomere 316.38 µm).

Mandible palp-shaped, translucent, pale brown, glabrous and smooth, proximally wide, but medially narrowed and slightly incurved, distally broadened into a knife-shaped apex (length of mandible 262.77 µm). Labrum reddish brown. Maxillary palp 2-segmented, dark brown, with dense hairs; 1 st segment short, ring-shaped, dark brown; 2 nd segment long, even thick rod-shaped, acutely tipped, elongated to ventral side, distally curved inward but not crossing to the other one; distinctly a thin brownish sclerotized strip extending latered between prementum and submentum; mouth opening circular (length of 1 st segment 30.88 µm, length of 2 nd segment 293.19 µm).

Thorax dark brown, strongly sclerotized. Pronotum trapezoidal, without hairs, narrower than interocular distance and twice as long as mesonotum, medially concaved on anterior margin and arcuately convexed on posterior margin, connected with mesonotum by pale brown pleural membrane (length of pronotum 123.96 µm, width 400.59 µm).

Mesonotum saddle-like (length of mesonotum 41.32 µm, width 458.08 µm); prescutum and scutum nearly as wide as pronotum, both with rounded lateral margins; scutellum transversely extending into a strip-shaped plate.

Metathorax well developed; prescutum nearly pentagon, slightly bulge at middle, with triangularly protruding anterior margin; scutum separated into a nearly rectangular, anteriorly rounded, anterior part and a subtriangular posterior part by dark brown sutures; prescutum and scutum separated by a distinct V-shaped suture, but fused to each other posteriorly; scutellum semicircular, slightly produced on anterior margin, laterally margined dark brown; postlumbium lip-shaped, dark yellow; postscutellum long conical-shaped, gradually bending ventrad at posterior 2/3, with a blunt tip.

Legs pale brown, but femora slightly paler; coxae of fore- and midlegs broad and flat; trochanter of hindleg small, subtrapezoidal; tarsi 4-segmented, without tarsal claws; 1 st tarsomere trapezoidal, with one sensory organ; 2 nd –4 th tarsomeres subtriangular, gradually shortened (lengths of fore coxa, femur, tibia, and tarsi 328.02 µm, 408.64 µm, 317.41 µm, 264.56 µm, lengths of 1 st –4 th fore tarsi: 126.78 µm, 92.83 µm, 90.65 µm, 87.11 µm. lengths of mid coxa, femur, tibia, and tarsi: 468.50 µm, 208.89 µm, 223.10 µm, 278.36 µm, lengths of 1 st –4 th mid tarsi: 136.75 µm, 111.57 µm, 106.75 µm, 90.38 µm. lengths of hind trochanter, femur, tibia, and tarsi: 65.59 µm, 172.02 µm, 174.82 µm, 247.88 µm, lengths of 1 st –4 th hind tarsi: 112.17 µm, 111.14 µm, 106.14 µm, 95.33 µm).

Halteres slender, long, weakly sclerotized; proximally with a dark brown longitudinal vein-like line at middle, distal part ovoid (length of halter 507.69 µm).

Hind wing broad, fan-shaped, translucent, pale brown, with dark brown veins; C and Sc fused into a thick vein, not reaching anterior margin; R 1 almost ending at distal 1/4; R 2 detached, distally bifurcated; R 3 detached, reaching distal margin; R 4 weak, ending at middle; R 5 long but proximally detached, reaching distal margin; MA and CuA both simple and almost parallel, reaching distal margin; CuP weak, almost parallel to anal margin. Length of hindwing 1.61 mm.

Abdomen dark brown, dorsally much paler; 10-segmented; tergites II–V gradually narrowed but tergites V–VIII gradually widened; segment I not reduced; segments II and III large, completely covered by postscutellum. Segment IX, elliptical in caudal view, extending ventrally as an elongate and grooved subgenital plate; lateral margins strongly sclerotized and incurved; posterior margin slightly concaved. Segment X small, shovel-shaped, with dorsally curved lateral margins. Aedeagus hook-like, arcuately curved anteriorly, with arcuate distal margin; dorsal hook and ventral projection of equal length; dorsal hook straight, with acute tip, directed from body of aedeagus by acute angle; ventral projection thicker than dorsal hook. Length of aedeagus 377.22 µm.

Female and host. Unknown.

Type material. Holotype ♂, CHINA: Guizhou Prov., Guiyang, Huaxi [26°23′42.97″N, 106°39′18.71″E], Heichunhe , 19.VIII.1988, collected by light trap, Chikun Yang ( CAU).

Etymology. The specific epithet is derived from Latin arcuatus , in reference to the arcuately curved aedeagus apex in the new species.

Remarks. This new species and M. pachynathus sp. nov. are distributed in the same province, i.e. Guizhou Prov. of southwestern China, and both species share some similar characters, e.g. the long 3 rd flabellum, which almost reaches tip of 7 th antennomere, and the distinctly bifurcated R 2. However, M. arcuatus sp. nov. differs from M. pachynathus sp. nov. by the thin and incurved maxillary palp and the strongly curved apex of aedeagus.

This new species also resembles Myrmecolax malayensis Kathirithamby, 1993 from Southeast Asia by having similar distally bifurcated detached vein with anterior branch directed toward wing base, but it differs from M. malayensis by the conspicuously longer body length and the long and curved apex of aedeagus.

A key to the species of Myrmecolax from Asia, based on the males, is given below, including 13 extant species. However, in the present key, Myrmecolax genitalis Kifune & Hirashima, 1989 from Laos is excluded because the description lacks the character of antenna, which is important for specific identification, due to damage of the holotype.

Figures

FIGURE 4. Myrmecolax arcuatus sp. nov., holotype male. A. Head, thorax and abodomen, dorsal view; B. Left antenna; C. Right wing. Scale bars = 250 µm.

FIGURE 5. Myrmecolax arcuatus sp. nov., holotype male. A. Foreleg; B. Midleg; C. hindleg; D. Mandible and maxillary palpi, ventral view; E. Aedeagus, left lateral view. Scale bars = 250 µm for A–C & E; Scale bars = 100 µm for D.

FIGURE 6. Myrmecolax arcuatus sp. nov., holotype male. A. Head, frontal view; B. Head, left lateral view. Scale bars = 500 µm.