Two new species of the genus Xanthochlorus from China (Diptera, Dolichopodidae, Xanthochlorinae)

Abstract The subfamily Xanthochlorinae comprises a single genus Xanthochlorus, and is rare in collections. Previously, there were four known species in the genus Xanthochlorus from China. In this paper, the species of the Xanthochlorus from China are reviewed. The following two species from Gansu Province of China are described as new to science: Xanthochlorus gansuensis sp. n. and Xanthochlorus tewoensis sp. n. A key to species of the Xanthochlorus from China is provided.


Introduction
The subfamily Xanthochlorinae comprises only the single genus Xanthochlorus Loew. Compared to the other subfamilies of Dolichopodidae, most of which have high diversity, the genus Xanthochlorus has a low species number. There are presently 18 known species of Xanthochlorus in the world (Yang et al. 2006, 2011, Grichanov 2017, with only four species known in China: Xanthochlorus chinensis Yang & Saigusa, X. nigricilius Olejníček, X. henanensis Wang, Yang & Grootaert and X. tibetensis Xi, Wang & Yang (Olejníček 2004, Yang and Saigusa 2005, Wang et al. 2008, Yang et al. 2011, Xi et al. 2015. They have been reported from Shaanxi, Henan, and Tibet, which are, respectively, in the northwest and middle of China. Gansu Province (32°31'-42°57'N, 92°13'-108°46'E) is located in the northwest of China and lies between the Tibetan Plateau and the Loess Plateau. The topography here is quite complicated, with mountains, basins, and deserts intersecting each other, which consequently also brings a complexity of the climates to this region. Due to a lack of precipitation, the northern part of Gansu province is dry and harsh all year round. However, the climate in the south of Gansu province is wet and mild, which leads to an abundant vegetation. These various environments contribute to the high species diversity of Gansu province. However, the investigation of the long-legged fly fauna here is still underway. In this paper two new species of the Xanthochlorus from Gansu province of China are reported and a key to the males of Xanthochlorus in China is provided. This is also the first time Xanthochlorus has been reported from Gansu province.

Xanthochlorus chinensis Yang & Saigusa, 2005
Xanthochlorus chinensis  brown with pale gray pollen, width of face equal to length of first flagellomere. Postocular bristles all yellow. Two oc, two vt. Antenna (Fig. 4) yellow; first flagellomere nearly quadrate, 0.57 times as long as wide; arista brown, basal segment 0.09 times as long as apical segment. Proboscis yellow with yellow hairs; palpus yellow with yellow hairs.
Thorax yellow with pale gray pollen. Hairs and bristles on thorax black. Pteropleuron and latero-tergite each with a single black spot. Five strong dc, acr absent, one strong h, two strong npl, one strong su, one strong prsu, one strong sa, one strong pa; scutellum with a pair of sc. Propleuron with white hairs and a long yellow bristle on lower portion. Legs yellow. Hairs and bristles on legs black. Fore coxa with six bristles; middle and hind coxae each with a single black outer bristle. Fore tibia without distinct bristle; middle tibia with one ad, one pd, and four apical bristles; hind tibia with two apical bristles. Mid and hind femora without preapical bristles. Relative lengths of tibia and 5 tarsomeres LI 6.0 : 4.0 : 1.6 : 1.2 : 0.8 : 0.7; LII 6.0 : 4.0 : 1.6 : 1.2 : 0.8 : 0.7; LIII 9.4 : 2.8 : 1.9 : 1.2 : 0.8 : 0.6. Wing hyaline, veins brown; costal callus indistinct; M gently bent apically, M and R 4+5 parallel apically; CuAx ratio 0.47. Squama yellow with yellow hairs. Halter yellow.
Remarks. The new species is somewhat similar to X. chinensis Yang and Saigusa, but can be separated from the latter by the quadrate first flagellomere, the yellow midposterior area of the mesonotum and the two protuberances on the ventral lobe of the surstylus. In X. chinensis, the first flagellomere is semicircular, the mid-posterior area of the mesonotum is black, and the ventral lobe of the surstylus is irregularly furcated at tip Saigusa 2005, Yang et al. 2011: p 1539, fig 987b).
Etymology. The specific name refers to the type locality of Tewo.
Thorax yellow with pale gray pollen. Hairs and bristles on thorax black. Mid-posterior area of mesonotum blackish; mid-basal area of scutellum blackish; pteropleuron and latero-tergite each with one black spot. 5 strong dc, acr absent, one strong h, two strong npl, one strong su, one strong prsu, one strong sa, one strong pa; scutellum with one pair of sc. Propleuron with white hairs and one long yellow bristle on lower portion. Legs yellow. Hairs and bristles on legs black. Fore coxae with 5-6 bristles; middle and hind coxae each with one outer bristle. Fore tibia without distinct bristles; middle tibia with two ad, one pd, and four apical bristles; hind tibia with three apical bristles. Mid and hind femora without preapical bristle. Relative lengths of tibia and 5 tarsomeres LI 3.0 : 1.5 : 0.8 : 0.6 Abdomen yellow with pale gray pollen. Hairs and bristles on abdomen black. Male genitalia (Figs 7-9): Epandrium longer than wide; dorsal lobe of surstylus yellow, wide basally, nearly quadrate, apically concaved with two bristles; ventral lobe of surstylus pale brown, wide basally, band-like, apically rounded with two bristles; cercus ovate basally, apically finger-like with bristles; hypandrium brown, rather short with short strip-like lateral protuberance. Female (Fig. 3). Body length 2.6 -2.8 mm. Wing length 2.7-2.9 mm. Types. Holotype male, CHINA, Gansu, Tianshui, Dangchuan Linchang, Maicaogou; collected by sweeping nets in grassland, 2015.VII.17, Xiaoli Li (CAU). Paratypes: nine males, 13 females, collecting information same as the holotype (CAU).
Remarks. The new species is somewhat similar to X. henanensis Wang, Yang and Grootaert, but can be separated from the latter by the first flagellomere apically without acute corner and by the lack of acrostichals. In X. henanensis, the first flagellomere has an acute lower apical corner and 3-4 acrostichals are present (Wang et al. 2008, Yang et al. 2011 1540, fig 988a).
Etymology. The specific name refers to the type locality Gansu.