A New Species of Scirtothrips Infesting Ginkgo biloba in Eastern China

A new thrips species, Scirtothrips ginkgoe Mirab-balou, Tong, and Chen, sp. n. (Thripidae: Thripinae) from Eastern China, collected on the leaves of Ginkgo biloba L. (Ginkgoaceae), is described and illustrated based on the male and female adult stage and the larva.


Introduction
Scirtothrips Shull (Thripidae: Thripinae) consists of very small, active thrips that breed on the young leaves of plants, although adults may at times be found on flowers (Hoddle and Mound 2003;Hoddle et al. 2008). Several of them, such as S. dorsalis, S. citri, and S. perseae, are serious pests on perennial fruits, vegetables, and ornamental crops (Mound and Marullo 1996;Nakahara 1997;Hoddle and Mound 2003;Masumoto and Okajima 2007;Hoddle et al. 2008). This genus includes 102 described species in the world (Mound 2012), of which seven species have been recorded from China (Mirab-balou et al. 2011). Among them, only S. dorsalis is widely distributed in China.
The ginkgo tree, Gingko biloba L. (Gingkoaceae) (Figure 1) is the oldest living tree species, with at least a 200 million year history (Shen et al. 2004). It is probably native to China, and has been widely cultivated and introduced since an early period in human history because of its various uses as food and traditional medicine (Fu et al. 1999). Extracts of Ginkgo leaves contain flavonoid glycosides and terpenoids (ginkgolides, bilobalides), and have been used pharmaceutically (Dekosky et al. 2008;Snitz et al. 2009). In this paper, we describe a previously unknown species of the genus Scirtothrips that was discovered damaging leaves of ginkgo trees in Hangzhou, Eastern China.

Materials and Methods
Specimens were collected from Hangzhou, Zhejiang province, eastern China during May-August 2011. In a laboratory, thrips were prepared and mounted on glass slides using the method of Mirab-balou and Chen (2010).

Morphological
terminology follows Masumoto and Okajima (2007), and Kucharczyk (2010). All descriptions, measurements, and photos were made with a Leica DM IRB microscope, a Leica MZ APO microscope with a Leica Image 1000 system. The type specimens were deposited in the Institute of Insect Sciences, Zhejiang University, Hangzhou, China. Body length is in millimeters (mm), and other measurements are in micrometers, unless otherwise stated.

Distribution. China: Zhejiang Province.
Etymology. This species is named after the generic name of its recorded host, Ginkgo.
Economic Importance. This species feeds on ginkgo foliage. The leaves become bronzed to yellow color when the thrips are found in high populations (Figure 2).
Remarks. This new species is most similar to S. dorsalis, but is readily distinguished from the latter by the following characteristics: absence of brown markings on abdominal tergites ( Figure 16) (versus the presence of brown markings medially on abdominal tergites III-VII in S. dorsalis) ( Figure 17); antecostal ridges of tergites pale brown and shaded on sternites (versus dark brown on both tergites and sternites); head and pronotum yellow or grayish white ( Figure 13) (versus head pale brown at apex of frons and pronotum with brown marking laterally in S. dorsalis) ( Figure 12); and antennal segments I-II light yellow ( Figure 14) (vs. antennal segment I pale and II-III grey in S. dorsalis) (Figure 15). The second instar larvae of this new species and S. dorsalis are similar in having reticulate sculpture on the head and pronotum, but the head with setae D4 is acute in this new species (Figure 20) while capitate in S. dorsalis; the body of the new species is also paler than S. dorsalis.
This new species is also distinguished from S. asinus Wang by the following characteristics: forewing second vein with two setae (versus three setae in S. asinus); antecostal ridge of abdominal tergites pale brown (versus dark brown in S. asinus); male without drepanae on abdominal tergite IX (versus with drepanae in S. asinus). Among remaining species recorded from China (except S. dorsalis and S. asinus), this new species is easily characterized by microtrichia extending fully across median area on posterior half of abdominal sternites, and having tergites without dark antecostal ridges. Abdominal sternites with microtrichia do not extend across median area in other remaining Chinese species.
According to the key and descriptions in Mound and Stiller (2011), this new species is similar to S. oligochaetus (Karny), but is readily distinguished from the latter by having three discal setae on the lateral microtrichial fields of abdominal tergites (versus 4-5 discal setae in S. oligochaetus); forewing brown (versus pale in S. oligochaetus); and sternites with microtrichia extending fully across median area on posterior half (versus with microtrichia covering median area except on anterior half in S. oligochaetus).