Two new species of Stenochironomus Kieffer (Diptera, Chironomidae) from Zhejiang, China

Abstract Two new species of Stenochironomus Kieffer (Diptera: Chironomidae: Chironominae), Stenochironomus brevissimus sp. n. and Stenochironomus linanensis sp. n., are described from China and the male imagines are illustrated. Stenochironomus brevissimus sp. n. can be separated from the so far known species by having very short and small, spatulate superior volsella with two long setae, whereas Stenochironomus linanensis sp. n. is easily separated from the other species of Stenochironomus by the following characters: wings transparent, body yellow, superior volsella finger-like, with nine long setae, elongated inferior volsella with four long setae and one well developed terminal spine; tergite IX with 10−15 long setae medially. A key to the males of Stenochironomus occurring in China is given.


Introduction
Stenochironomus Kieffer, 1919 is a species-rich genus with worldwide distribution, occurring in all biogeographical regions except in Antarctica (Cranston et al. 1989). The genus was erected by Townes in 1945 based on Chironomus pulchripennis (Coquillett, 1902) (Spies and Saether 2004). The larvae are easily found mining decayed leaves or wood in freshwater habitats ranging from small ponds and swamps to fast-flowing streams and rivers (Cranston et al. 1989). Based on the different hosts of larvae and pupae, Borkent (1984) erected two subgenera: Stenochironomus s. str. Kieffer (larvae and pupae mine dead submerged wood) and Petalopholeus Borkent (larvae and pupae mine dead submerged leaves). This subdivision has not been adopted by subsequent authors, because immature stages are known only for a few species, which makes difficult to ascribe them to any subgenus (Pinho et al. 2005, Andersen et al. 2008, Qi et al. 2008, Dantas et al. 2010, Zorina 2010. To date, there are 97 species recorded around the word: 24 species from the Palaearctic Region, 17 from the Nearctic Region, 30 from the Neotropical Region, 16 from the Oriental Region, 16 from the Afrotropical Region and 4 from the Australasian Region (Qi et al. 2011, Reis et al. 2013.
Zhejiang Province is located in the Chinese central subtropical region, which has a humid monsoon climate. In Zhejiang, three species of Stenochironomus [S. koreanus Borkent, 1984, S. nubilipennis Yamamoto, 1981 andS. satorui (Tokunaga & Kuroda, 1936)] have been recorded (Wang 2000, Qi et al. 2011. In this paper, two new species of Stenochironomus from Zhejiang, Oriental China, are described and illustrated.
A key to the males of Stenochironomus from China is presented.

Materials and methods
The morphological nomenclature follows Saether (1980). Measurement methods follow Qi et al. (2012). The material examined was slide-mounted, following the procedure outlined by Saether (1969). Specimens have been deposited in the College of Life Science, Taizhou University, China.
Abbreviations of parts measured are as follows:
Etymology. The specific epithet is a Latin adjective "brevissimus", meaning the shortest, and refers to the superior volsella, which is the shortest in the genus.
Remarks. S. brevissimus sp. n. is similar to S. hainanus Wang, 2008 andS. okialbus Sasa, 1990 in having short and small superior volsella, but can separated from these species by the differences given in Table 2.
Distribution. The species is known from Zhejiang Province of Oriental China.