A new species of Gadirtha Walker (Nolidae, Eligminae): a proposed biological control agent of Chinese tallow (Triadica sebifera (L.) Small) (Euphorbiaceae) in the United States

Abstract Gadirtha fusca sp. n., is described from Guangxi Province, China. Gadirtha fusca differs in forewing color and pattern, male and female genitalia, and in larval pattern from all other species of Gadirtha. Gadirtha fusca has been evaluated as a potential biological control agent for Chinese tallow (Triadica sebifera (L.) Small, Euphorbiaceae) in the southeastern United States. Adult, male and female genitalia, larva, and pupa are described, illustrated, and compared with Gadirtha impingens Walker.


Introduction
The genus Gadirtha Walker was revised by Holloway (2003) and included three species; the type species G. impingens Walker, G. pulchra Butler, and G. inexacta Walker. Gadirtha pulchra and G. impingens are the most widespread. Gadirtha pulchra ranges from the Indian Subregion, to the Ryukyu Islands in Japan, and Thailand, Singapore, New Guinea, and Queensland, Australia; G. impingens ranges from northern India and southern China to Queensland, the Bismarcks, and Solomons, (Holloway 2003) and from Honshu, Shikoku, Kyushu, and Tsushima in Japan (http://www.jpmoth.org). Gadirtha inexacta is found in northern India and Burma, and G. fusca in southern China.
A molecular phylogeny of Nolidae used eight genes to produce a stable phylogeny that consisted of eight strongly supported subfamilies (Zahiri et al. 2013). Holloway (2003) originally placed Gadirtha in the Collomeninae, but the results of Zahiri et al. (2013) moved all of the Eurasian genera formerly associated with Collomeninae to the subfamily Eligminae. Holloway (2011) preempted the placement of Gadirtha in Eligminae based on characters outlined in Zahiri et al. (2013). Members of Eligminae have an elongate and narrow forewing and in some genera the uncus is absent in the male genitalia. Species of Gadirtha have an elongate and narrow wing and the uncus is replaced by stiff, hairlike setae.
Gadirtha fusca is being considered as a potential biocontrol agent against Chinese tallow (Triadica sebifera (L.) Small, Euphorbiaceae) in the southeastern United States and formal description is critical to this process. Once G. fusca is introduced it will be the largest Nolidae in North America and can easily be distinguished by its elongate forewing with a truncate apex, dark gray forewing ground color with reduced pattern, and a dark gray hind wing. These characters will also distinguish it from other Gadirtha species in Asia. This paper describes the last instar, pupa, adult, and male and female genitalia.

Methods and materials
Images of adults and genitalia were taken with a digital camera, macro lenses, and a pulsed xenon flash. Images were enhanced with Adobe Photoshop® CS4.
Genitalia dissections follow Pogue (2002), except the genitalia were mounted in euparol. Vesica was inflated with 99% isopropyl alcohol and stained in Orcein.
Comparisons of forewing ground color and pattern, hind wing color, and male and female genitalic structures were compared with all species of Gadirtha using Holloway (2003). The male genitalia of G. fusca most closely resembled G. impingens, but differences are illustrated by comparing Figures 5 and 6.
Material used in this study is deposited in the following institutions: The Natural History Museum, London (BMNH), Canadian National Collection, Agriculture Canada, Ottawa, Canada (CNC), and National Museum of Natural History, Smithsonian Institution, Washington, DC (USNM).
Diagnosis. In the male genitalia G. fusca is most closely related to G. impingens as they share the same 90° angle in the apex of the costa in the valve (Figs 5-6). The aedeagus is abruptly bent medially in G. fusca (Fig. 7) and curved beyond the midpoint in G. impingens (Fig. 8). In G. pulchra and G. inexacta the costal arm of the valve is slightly bent, not curved at a 90° angle. The costal arm of the valve in G. inexacta bears a dorsal triangulate projection near its apex (see fig. 502 in Holloway (2003)) and this projection is absent in G. pulchra see fig. 500 in Holloway (2003). In the female genitalia the ostium bursae in G. fusca is membranous internally with a thin, sclerotized outer margin shaped like an up-side-down conventional incandescent light bulb (Fig. 9); compared to a heavily sclerotized ostium bursae that is strongly curved ventrally (Fig. 10) in G. impingens. Gadirtha fusca cannot be confused with any of the other three species of Gadirtha with its gray forewings, subdued pattern, and solid dark gray hind wings (Figs 1-2). Forewing ground color is brown to brownish gray in G. impingens with distinct black costal spots (Figs 3-4), contrasting with the dark gray forewing and faint costal spots in G. fusca. Hind wing in G. fusca is dark gray and white basally and dark brown distally in G. impingens. Only G. fusca and G. impingens are distributed in China.
Larvae have a pale green to yellow-green ground color with elongate black and white setae. Pattern differences are distinct between species. Gadirtha fusca has a distinct, wide black dorsal stripe with large, ovate, black spots on A1, A2, and A8 . In G. impingens, the dorsal black stripe can be absent or if present, a thin line on each segment that is not contiguous; black ovate spots on A1 and A2 are smaller than in G. fusca and a small black round spot on A8 (http://jpmoth.org/Nolidae/ Eligminae/Gadirtha_impingens.html). In G. pulchra the black spots are ringed with blue on T2-A4, with the largest spots on T3 and A1 (colour plate 12, fig. F in Murphy 1990).
Etymology. The specific epithet refers to the dark grayish brown ground color of the forewing.
Biology. Gadirtha fusca overwinter as eggs on leaves and branches of Chinese tallow and hatch in May. Larvae feed on leaves and complete six instars in 15 days and can cause extensive defoliation, especially during the last three instars. There can be 4-5 generations per year in Hubei Province (Wang et al. 2012).
Distribution. East central and southeastern China. Discussion. It is curious why G. fusca was misidentified in the biocontrol literature as G. inexacta (Wang et al. 2012). In reviewing Holloway (2003), G. inexacta does not occur in China and the life history is unknown. The more obvious misidentification would be with G. impingens, which does occur in China, larvae are known to feed on species of Euphorbiaceae, and morphology of the male genitalia are similar.