Siamothrips balteus, a new species of Scirtothrips genus-group from China (Thysanoptera, Thripidae)

Abstract The third species of the genus Siamothrips Okajima, Siamothrips balteus sp. n., is described from China. The new species is characterised by the abdominal tergite II uniformly brown, III–VII with a brown area medially but pale on lateral thirds, tergite VIII smooth medially, tergite X with 3–4 rows of microtrichia medially, and abdominal sternite VII with one pair of discal setae laterally. A key to the three species has been constructed and is presented here.


Introduction
Siamothrips is a small genus that was erected by Okajima (1990) based on a single species, S. argus Okajima, from Thailand. Subsequently, Ng and Mound (2015) described a second species in the genus, S. initium Ng & Mound from Malaysia, and a third species is described here from southern China. Although the generic relationships of the genus are not clear, Okajima (1990) suggested placing it in the tribe Sericothripini, but more recently Masumoto and Okajima (2007) suggested Siamothrips might be a member of the Scirtothrips genus-group.

Materials and methods
The thrips were collected by beating vegetation over a white plastic tray using a stick, and then sorted and preserved in 90% alcohol. Examined specimens were mounted with Canada balsam using the method outlined by Zhang et al. (2006). Details of the morphological structures were examined with a ZEISS Imager A1 microscope, the photos were taken by the Photometrics CoolSNAP camera, and the figures were subsequently processed with Adobe Photoshop CS6. All type specimens are deposited in the Insect Collection, South China Agricultural University (SCAU).  Figures 1-10. Siamothrips balteus sp. n. 1 female habitus 2 head 3 pronotum 4 meso-and metanotum 5 antenna 6 fore wing 7 meso-and metasternum 8 ovipsitor 9 abdominal sternites VI-VII 10 abdominal tergites VII-X. and submedian setae on mesoscutum arranged in a transverse line; sculpture on mesoand metascutum bearing inner markings. Abdominal tergite VIII smooth medially; tergite X with 3-4 rows of microtrichia medially; abdominal sternite VII with one pair of discal setae laterally and median pair setae situated at posterior margin.

Key to species of Siamothrips (female)
Description. Female (macropterous) (Fig. 1): Body pale to brown, anterior 3/4 margin of head yellowish brown; antennal segments I-II pale, III light brown, IV-VIII uniformly brown; pronotum uniformly light yellowish brown; posterior half of mesonotum and metanotum brown; all legs pale but tarsi slightly darker at extreme apex; fore wing brown except pale at basal 1/3 and apical 1/7, clavus brown; abdominal tergite I pale, II uniformly brown, III-VII with brown area medially but pale lateral thirds, and antecostal ridges darker medially, VIII-X uniformly yellowish brown; abdominal sternites pale including antecostal ridges.
Head approximately twice as wide as long, widest across eyes, slightly projecting in front of compound eyes; dorsal surface of head including ocellar triangle sculptured with transverse anastomosing striae, but the frons with longitudinal striae (Fig. 2); eyes bulging and pilose without pigmented ommatidia; cheeks very short and almost parallel; three pairs of ocellar setae present, setal pairs I and III subequal in length, pair II longest; pair I situated in front of ocelli, pair II situated on margin or outside of ocellar triangle near eyes, pair III arising on tangent between anterior margins of hind ocelli (Fig. 2); two pairs of postocular setae; mouth-cone long but never extending beyond posterior margin of pronotum; maxillary palps 3-segmented, terminal segment long, slightly shorter than the combined length of other two segments. Antennae 8-segmented (Fig. 5), segment I without dorsal apical setae, II without campaniform sensilla, with four rows of microtrichia dorsally; forked sensoria on III-IV, not reaching more than one-third the length of succeeding segment, V-VI each with an small outer sense cone; III-VI with about four rows of microtrichia on both dorsal and ventral surfaces. Pronotum (Fig. 3) trapezoidal with approximately 35-40 fine setae including marginal setae, without long posteroangular setae; dorsal surface sculptured with distinctly transverse anastomosing striae but on posterior half, the striae are irregular medially. Mesonotum (Fig. 4) with irregular transverse anastomosing striae bearing inner granules, without campaniform sensilla; median and submedian setae arranging in a transverse line. Metanotum (Fig. 4) sculpture irregular longitudinal reticulate medially with inner markings, lateral area with longitudinal lines bearing feeble inner granules, without campaniform sensilla; median setae usually situated near anterior margin (sometimes at anterior margin), submedian setae situated at anterior margin; median setae slightly shorter than submedian setae. Meso-and metasternum each with approximately 20 long fine setae, meso-and metafurcae with spinula (Fig. 7). Fore wing (Fig. 6) first vein with 11-12 setae, second vein without setae, clavus with three veinal and one discal setae; posteromarginal fringe cilia weakly wavy. Tarsi 2-segmented.
Abdominal tergites II-VII with closely spaced rows of ciliate microtrichia on lateral thirds, S1 setae small, slightly longer than the distance between their bases, but S1 setae on tergites VIII-IX well developed and long, approximately twice as long as distance between their bases; tergites II-VIII smooth medially without any rows of microtrichia, tergite VIII with complete posteromarginal comb (Fig. 10); tergite IX without campani-form sensilla or microtrichia, but tergite X with 3-4 rows of microtrichia medially (Fig.  10). Abdominal sternites II-VII with rows of ciliate microtrichia across median area, at least on posterior halves, posterior margin with fringe of microtrichia; segment II with three pairs of long posteromarginal setae, III with four pairs of long posteromarginal setae; IV-VII with five pairs of long posteromarginal setae, all primary setae of sternites situated at posterior margins; sternite VII with one pair of discal setae laterally (Fig. 9). Ovipsitor (Fig. 8) straight and elongate, slightly longer than twice the length of pronotum.
Male unknown.
Etymology. The specific epithet is from the Latin balteus, meaning "belt or waistband," in reference to the abdominal tergite II being entirely brown in contrast to largely pale colouration of the other tergites.
Remarks. This new species is most similar to S. initium Ng & Mound, 2015 from Malaysia; however, it can be distinguished from these two species by the key above.