Samia watsoni (Oberthür, 1914)

Wu, Yujie, Peigler, Richard S. & Liu, Zhengyang, 2025, Ecological observations on the genus Samia Hübner, 1819 (Lepidoptera, Saturniidae) of China, especially the natural hostplants, Nota Lepidopterologica 48, pp. 251-268 : 251-268

6. Samia watsoni (Oberthür, 1914)

Figs 2 E, F , 4

Material examined.

ZHEJIANG: ( AD): Three ovum clusters and all laid in single layer, five unhatched, four unhatched and four hatched (Fig. 3 D ), all attached on the leaf upperside; Stewartia gemmata ( Theaceae ); Dashuwang, West Tianmushan, Lin’an District, Hangzhou, 902 m, 954 m and 963 m; 14 and 20 August 2023. ( AD): Four ovum shells, side by side and single layer, attached on the leaf upperside (Fig. 3 C ), and more than thirty solitary L 1– 4 larvae on the leaf undersides (Fig. 3 G, I ); Pterostyrax corymbosus ( Styracaceae ); Dashuwang, West Tianmushan, Lin’an District, Hangzhou, 878 m; 13 August 2023. ( AD): More than fifteen solitary L 3– 5 larvae on the leaf undersides; P. corymbosus ; Gaoqiaowu, West Tianmushan, Lin’an District, Hangzhou, 857 m; 16 August 2023. ( AI): One ovum, attached on the leaf upperside; P. corymbosus ; Qingliangfeng National Nature Reserve, Lin’an District, Hangzhou, 623 m; 28 June 2021. ( OD): Thirteen solitary mature larvae; P. corymbosus ; Tianmushan National Nature Reserve, Lin’an District, Hangzhou, ca. 900 m; 09 October 2022.

Notes.

S. watsoni is regarded as the sister group to all other Samia ( Peigler and Naumann 2003: 71; Peigler and Liu 2022; Lu et al. 2022). Its habitats cover montane broadleaf forests in subtropical China, with the type locality in Mount Emei of Sichuan, while the population in Taiwan has been subjectively considered as a sub- ( Kishida 1982) or full species ( Naumann et al. 2014). Peigler & Naumann (2003: 170) diagnosed S. watsoni as: “ Readily separated from other species in the genus by the large size, burgundy or reddish-brown ground color, crescents containing a lot of the transparent component, orange patch on the forewing apex, and a second black eyespot on the outer tip of the forewing. ” All new observations suggest that females tend to lay eggs on the upper sides of leaves, as previously reported by Peigler and Liu (2022), in which the complete life history of S. watsoni was also described for the first time. In the same work, trials suggested that this species is possibly oligophagous on the family Styracaceae (based on the population from Zhejiang), but the authors assumed it utilizes other plants across its wider habitat; here we supplement a new host record from Theaceae . Since 2024, Zhengyang Liu has conducted multiple attempts in Kunming, Yunnan to rear S. watsoni originating from Guangxi using Styrax grandiflorus , P. corymbosus , and Sinojackia xylocarpa ( Styracaceae ), yet all larvae failed to develop beyond L 2. In late April of 2025, many L 1 larvae from a wild-caught female from Fangchenggang, Guangxi, also died after feeding on P. corymbosus . However, the 15 dying individuals readily accepted Symplocos paniculata ( Symplocaceae ) and progressed rapidly to the next instar. From this cohort, nine cocoons were obtained (other larvae succumbed to disease between L 3–4, unrelated to host plant suitability), and three male moths eventually emerged in early July (the remaining pupae desiccated due to arid rearing conditions). Notably, all of them exhibited melanic phenotypes (Fig. 4 A – E ). In the absence of additional material for further study, we preliminarily hypothesize that this form may be diet-induced, given that their mother displayed the typical reddish-brown form. Nevertheless, further experimentations are needed. Additionally, we learned that all caterpillars of the Taiwanese population consistently failed to pass the first moult after feeding on various native Styracaceae genera (Jinxiu Liang, personal communication to Zhengyang Liu, 28 May and 14 June 2022). Although the red dorsal scoli during mature instar [L 5] of S. watsoni is reminiscent of S. kohlli (Fig. 3 O ) (see also section 3), the former usually has thinner white waxy powder on epicuticle, and a plumper body with reduced subdorsal and lateral [L] scoli. In captivity, there were quite a few individuals observed leaving the host plant to spin dark brown cocoons, either peduncled strongly on trees or weakly between fallen leaves (Fig. 3 Q ). We are not sure how many generations per year this species attains in the wild but based on captive and field observations there might be two or more seasonal flights, as suggested by Lemaire and Peigler (1982).

Figures

Figure 2. Adults of Samia spp. of China, dorsal views. A. S. ricini ♂, Longzhou County, Chongzuo, Guangxi, ca. 130 m, July 2023; B. S. ricini ♀, Longzhou County, Chongzuo, Guangxi, ca. 130 m, July 2023; C. S. canningi ♂, Menglun Town, Mengla County, Xishuangbanna, Yunnan, ca. 650 m, May to November 2022; D. S. canningi ♀, Menglun Town, Mengla County, Xishuangbanna, Yunnan, ca. 650 m, May to November 2022; E. S. watsoni ♂, Nibashan, Yingjing County, Ya’an, Sichuan, ca. 3200 m, 08 June 2023; F. S. watsoni ♀, Nibashan, Yingjing County, Ya’an, Sichuan, ca. 3200 m, 08 June 2023. Scale bar: 3 cm.

Figure 3. Preimaginal materials of Samia spp. of China. A – I, K – M, P. Individuals photographed in the wild. N, O, Q. Captive individuals. A. Ova of S. wangi on leaf underside of Styrax sp., Hangzhou; B. Ovum shells of S. kohlli on leaf underside of Z. armatum, Kunming; C. Ovum shells of S. watsoni on leaf upperside of P. corymbosus, Hangzhou; D. Ovum shells of S. watsoni on leaf upperside of S. gemmata, Hangzhou; E. Larval cluster of S. wangi L 3, dorsal view, on leaf underside of H. acerba, Hangzhou; F. Larval cluster of S. kohlli L 2 (pre-ecdysis), dorsal view, on leaf underside of Z. armatum, Kunming; G. S. watsoni L 2, dorsal view, on leaf underside of P. corymbosus, Hangzhou; H. S. kohlli L 3, dorsal view, on the leaf underside of C. nepalensis, Kunming; I. S. watsoni L 4, dorsolateral view, on leaf underside of P. corymbosus, Hangzhou; J. S. cynthia L 5 (mature), dorsolateral view, on C. officinarum; K. S. wangi L 5 (mature), lateral view, on S. japonica, Hangzhou; L. S. kohlli L 5 (mature), lateral view, on C. nepalensis, Kunming; M. S. canningi L 5 (mature), lateral view, on Zanthoxylum sp., Xishuangbanna; N. S. ricini L 5 (mature), lateral view, on C. nepalensis; O. S. watsoni L 5 (mature), lateral view, on P. corymbosus; P. Cocoon of S. wangi, on C. officinarum, Shanghai; Q. Cocoon of S. watsoni, on P. corymbosus.

Figure 4. Melanic (aberrant) males of Samia watsoni from Fangchenggang, Guangxi, reared in Kunming, Yunnan in April – July 2025, using the host plant Symplocos paniculata (Symplocaceae). A and B represent the same individual; C – E represent another individual. A. Entire moth, dorsal view; B. Thorax and abdomen, lateral view; C. Hindwing crescentic window, dorsal view; D. Antenna, dorsal view; E. Forewing apex, dorsal view.