Introduction

The genus Phthorarcha Meyrick, 1892 is a member of the subfamily Alsophilinae. The species of Phthorarcha are active in cold season, and the females are apterous ( Kostjuk et al. 2020). Meyrick (1892) established Phthorarcha and mentioned primigena Staudinger as the type species. Later, Staudinger (1895) described Anisopteryx primigena Staudinger, 1895 for the first time. Fletcher (1979) mentioned: “Phthorarcha was nomenclatural available from 1892, but the sole species included by Meyrick was a nomen nudum until described by Staudinger in 1895”.

Recently, Kostjuk et al. (2020) reviewed the Central Asian species of Phthorarcha, described a new species, Phthorarcha haberhaueri Kostjuk, Mironov & Viidalepp, 2020, and gave some diagnoses of the genera Phthorarcha, Alsophiloides Inoue, 1961 and Chimaphila Nakajima & Wang, 2013. Until now, four species have been recognized including one species recorded from China ( Prout, 1912-1916; Parsons et al. 1999; Viidalepp, 1986, 1987; Nakajima & Wang, 2013; Kostjuk et al. 2020).

During recent studies in the collection in IZCAS, we have discovered one new species of Phthorarcha. The purpose of this paper is to describe a new species of Phthorarcha from Gansu of China: Phthorarcha pallidia Xian & Jiang sp. n. and provide diagnostic characters of the new taxa.

Material and methods

Specimens used in this study are deposited in IZCAS-Institute of Zoology, Chinese Academy of Sciences, Beijing, China. Terminology for wing venation follows the Comstock-Needham System ( Comstock, 1918) as adopted for Geometridae by Scoble (1992) and Hausmann (2001); that for genitalia follows Pierce (1914, reprint 1976), Klots (1970), and Nichols (1989). Photographs of moths were taken with a digital camera. Composite images were generated using Auto-Montage software version 5.03.0061 (Synoptics Ltd). The plates were compiled using Adobe Photoshop software 7.0. Ink (Adobe Systems Software Ireland Ltd).

Taxonomy

Phthorarcha pallidia Xian & Jiang sp. n. ( Figures 1-3)

Figures 1-3.
Phthorarcha pallidia Xian & Jiang, sp. n., holotype. 1. Adult. 2-3. Male genitalia. Scale bars =1.0 cm (figurel); 1 mm (figures 2-3).

Material examined (IZCAS). Holotype ♂, China: Gansu, Lanzhou, yuzhongxian, xinglongshan, 2200 m, 13-IV-2005, coll. Wang Xuejian. Paratypes: Gansu. 16 ♂♂, same data as holotype.

Description: Male adult ( Figure 1). Antennae dentate with very long fascicles of cilia, length of bristles more than three times of diameter of shaft. Frons grey. Labial palpus very small, not extending beyond frons. Tongue obsolete. Vertex, dorsal side of thorax and abdomen dark grey. Hind tibia without medial spurs. Forewing length: male 16-18 mm. Forewing slender, slightly pointed at apex, outer margin smooth; hindwing slender with apex rounded. Wings ground colour pale grey, forewing densely covered with dark greyish brown, hindwing translucent. Forewing with medial and postmedial lines blackish brown, serrate, distinct near costa and anal margin, and often dentate on each vein; blackish brown streak near Sc connected medial line and postmedial line; postmedial line edged with pale grey line outside; a blackish brow streak raising from apex and contacted with postmedial line at M ₁; a pale patch present inside of apex, extending to inner side of postmedial line and breaking postmedial line in most specimens; marginal line blackish brown, often dot-like at end of each vein; discal spot dark grey; fringes pale grey. Hindwing with discal spot dark grey; marginal line indistinct; fringes pale grey. Underside grey, discal spot of both wings blackish grey; postmedial line forming a blackish grey patch on costa.

Venation. Forewing: R ₁ shortly anastomosed with Sc and two accessory cells between radial veins or sometimes R ₁ free and one accessory cell between radial veins; R ₂ anastomosed with R ₁ and R _3-4; R ₅ rising after R ₃, near apex. Hindwing: Sc+R long anastomosed with upper margin of discal cell to near middle of cell; length of discal cell more than two third of maximum length in middle of hindwing; Rs and M ₁ rising from apical of discal cell or shortly stalked; M ₂ weak, almost absent.

Male genitalia ( Figures 2-3). Uncus triangular with apex slender. Gnathos absent. Valva short with apex almost triangular, rounded at tip; dorsal margin with two processes, basal one narrow and straight, medial one curved outward and slightly longer than basal one; juxta almost Y shaped, semicircle concaved on posterior margin. Saccus almost quadrate terminally with a tongue-like lobe. Aedeagus curved; manica bifurcate with apex tapering.

Diagnosis: The species is similar to Phthorarcha ishkoviViidalepp, 1986, However, it can be distinguished from P. ishkovi by the following characters: the streak between the apex and the postmedial line of the forewing is straighter; the distance from the medial line to the postmedial line on the costa of the forewing is less than twice the distance from the medial line to the postmedial line on the hind margin, while it is twice as broad on the costa than on the hind margin in P. ishkovi; the radian of the anal angle of the forewing is larger; the outer margin of the forewing is more inclined; the streak between the medial line and postmedial line is continuous, while it is broken and indistinct in P. ishkovi; the pale patch inside the apex usually extends to inner side of the postmedial line and breaks the postmedial line, while it rarely extends to inner side of the postmedial line and breaks the postmedial line in P. ishkovi; the marginal dots of the forewing are more indistinct. In the male genitalia, the apex of the uncus is slenderer; the apex of the valva is much narrower; the medial process on the dorsal margin of the valva is much slenderer and longer; the apex of the saccus is almost quadrate, while it is rounded in P. ishkovi.

Distribution: China (Gansu).

Etymology: The specific name is based on the Latin word pallidius. referring to the pale apex of the forewing.

Acknowledgements

We sincerely appreciate for Dr Jaan Viidalepp (Estonian University) and Prof. Min Wang (South China Agricultural University) for providing references for this study and to Prof. Dayong Xue (IZCAS) for his kind assistance. This project was supported by the National Science Foundation of China (31872966, 32170464, 31872967), National Science & Technology Fundamental Resources Investigation Program of China (Grant No. 2019FY101800), Biological Resources Programme of Chinese Academy of Sciences (Grant No. KFJ-BRP-017-45), the Ministry of Science and Technology of China (2015FY210300), and by a grant (Y229YX5105) from the Key Laboratory of the Zoological Systematics and Evolution of the Chinese Academy of Sciences.

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Author notes

*Autor para la correspondencia / Corresponding author