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Research Article
Rondotia melanoleuca sp. nov., a new wild-mulberry silkworm from China (Lepidoptera, Bombycidae)
expand article infoZhengyang Liu‡, Xiwen Cao§
‡ Unaffiliated, Zibo, China
§ Unaffiliated, Beijing, China

Corresponding author: Zhengyang Liu ( saturniidae@qq.com )

Academic editor: Rodolphe Rougerie
© 2024 Zhengyang Liu, Xiwen Cao.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation: Liu Z, Cao X (2024) Rondotia melanoleuca sp. nov., a new wild-mulberry silkworm from China (Lepidoptera, Bombycidae). Nota Lepidopterologica 47: 49-56. https://doi.org/10.3897/nl.47.109920
ZooBank: urn:lsid:zoobank.org:pub:3B0A899F-DCCB-4621-8F2F-C8346B740EF0
Open Access

Abstract

Several yellow larvae with black spots were discovered in the wild of Chinese Sichuan and Yunnan provinces, and were further raised in captivity. Reared adults exhibit a striking black and white wing pattern, and they represent unequivocally a new species, here described as Rondotia melanoleuca sp. nov. Molecular analyses suggest that this species could be sister to all previously known species of Rondotia.

Introduction

The genus Rondotia Moore, 1885 has long been identified as containing pests for the silk industry. Moore (1885) named this taxon in honor of the sericulturist Natalis Rondot, based on the type species Rondotia menciana Moore, 1885 from the Far East. For economic reasons, the biological characteristics and genomics of this white mulberry caterpillar have been studied in detail in China (e.g., Xu et al. 1994; Bai et al. 2001; Tang et al. 2018), while the other two members of the genus have received less attention. After the original description by Hampson (1893: 33–34), Rondotia diaphana (Hampson, 1893) from Myanmar, the species was later redescribed by Conte (1911: 72), and subsequently been reported from China (Wang et al. 2009), India, Thailand, and Vietnam (Zolotuhin and Witt 2009). In contrast, Rondotia lineata Leech, 1898 is a highland flyer endemic to the eastern edge of the Qinghai-Tibet Plateau and has rarely been mentioned in literature (Wang et al. 2015). Leech (1898) established the Korean Rondotia lurida Fixsen, 1887 as a synonym of R. menciana, and Conte (1911: pls. 5, 8) illustrated the three accepted taxa in colour. A recent taxonomic review shows the three species are closely related and monophyletic; macroscopically, these moths have similar wing patterns and venation (e.g., Wang et al. 2015).

We describe here a new species whose larvae were initially unidentified and collected in the wild in the Sichuan and Yunnan Provinces of China. Further morphological comparison and molecular data reveal its phylogenetic relationship within the genus Rondotia. It is currently only known from mid-elevation localities in southwest China.

Material and methods

A vernier caliper INSIZE 1108-150C 0–150 mm / 0.01 mm (± 0.02 mm) and magnifying lens PEAK 2008-50X 0–1.6 mm / 0.02 mm were used for measuring the dimensions of specimens. Genital preparations were made with 10% KOH solution (95 °C, 15 mins), and mounted the specimens on slides for observation and photography. Most of the color images were photographed with a NIKON D5500 and LAOWA 60 mm f/2.8–22 lens, but Fig. 1E–H were taken with a SONY α7 IV and objective lens 4× / 0.1. The images were focus stacked in PHOTOSHOP BETA, while visual optimization and stitching of figures was done with AFFINITY PHOTO 2.0.4.

Figure 1. 

R. melanoleuca sp. nov. A, B. HT: ♂ A. Dorsal view; B. Fore- and hindwings, ventral view; C, D. PT [A23072706], ♀: C. Dorsal view; D. Fore- and hindwings, ventral view; E–H. PT [A23072704], ♂: E. Sternum A8, dorsal view; F. Phallus, lateral view; G, H. Main genital sclerites of A9–10; G. Posterior view; H. Lateral view. Scale bar (left) for A–D: 1 cm; scale bar (right) for E–H: 1 mm.

A partial COI sequence (1235 bp) was newly sequenced from a paratype [unique identifier A23072707] of the new species, and the data has been submitted to NCBI [Genbank: OR051027]. We used the kit TIANGEN DP304 for DNA extraction (cryogenic grinding + silicon matrix adsorption) and PCR was conducted on a EASTWIN EDC810 thermocycler using 2× AceTaq Master Mix VAZYME P412 and the primer pair LYQ3/LYQ4 (Simon et al. 1994; 5’-CCTGGATCTTTAATTGGAGA-3’ / 5’-GGTAAAATTAAAATATAAACTTC-3’). Sanger sequencing was carried out using an ABI 3730XL sequencer.

The COI sequences of other bombycids were extracted from corresponding complete mitochondrial genomes, including Rotunda rotundapex (Miyata & Kishida, 1990) (Park et al. 2020: NC045528), Bombyx huttoni Westwood, 1847 (Peng et al. 2015: KP216766), Bombyx mandarina Moore, 1872 (Kim et al. 2022: OK358669), Bombyx mori (Linnaeus, 1758) (Zhang et al. 2022: MW158386), R. menciana (Kim et al. 2014: KJ647172) and Ocinara albicollis (Walker, 1862) (Deng et al. 2022: OM912596), as well as the outgroup Saturnia pyretorum Westwood, 1847 (Saturniidae) (Jiang et al. 2009: FJ685653). A partial COI sequence of R. diaphana was also available (Lin et al. 2019: MH817453) and used in our analyses.

The different sequences were aligned with MAFFT V7 using default parameters (Katoh et al. 2019). The ML [maximum-likelihood] tree was generated with IQ-TREE 2 (Minh et al. 2020), running with the best-fitting model TIM2 + F + G4 (Kalyaanamoorthy et al. 2017) and ultrafast bootstrapping (Hoang et al. 2018).

In this paper, we use the terminology of Liu (2023) for the description of preimaginal stages, that of Zwick (2009) for genitalia structures, and we follow Comstock (1918: 332) and Kristensen (2003) for wing venation. The following abbreviations are used: T1–3 = 1st–3rd thoracic segments; A1–10 = 1st–10th abdominal segments; R4 = 4th radius; M3 = 3rd median vein; CuA1 = 1st anterior cubitus; 1A = 1st anal vein.

Results

Rondotia melanoleuca Cao & Liu , sp. nov.

https://zoobank.org/CAB92047-39DC-47FB-8EBC-B1042D2487FC

Holotype [HT]

Imago, 1 ♂ ([unique identifier: A23072701]: China, Dafengding, Leshan, Sichuan Province, ca. 1500 m (Fig. 1A, B). A red label “HOLOTYPE” will be added, and the holotype will be deposited at the Institute of Zoology, Chinese Academy of Sciences, Beijing.

Paratypes [PTs]

Imagines, 4 ♂♂ [unique identifiers: A23072702–A23072705] and 4 ♀♀ (unique identifiers: A23072706–A23072709] (e.g., Fig. 1C–H), same data as for HT. All are preserved in the collection of the senior author (Beijing) with blue paratype labels.

Descriptions

Mature Larvae (Fig. 2E, F):

Figure 2. 

R. melanoleuca sp. nov. A–E, G–I. Specimens from the type locality; F. Specimen from Fugong County, Yunnan. A. Adult ♂, newly emerged, dorsal view, front light photography; B, C. Adult ♀, newly emerged, surround light photography: B. Dorsal view; C. Ventral view; D. Adult ♂, natural resting condition, dorsolateral view; E. Mature larva, dorsolateral view; F. Mature larva, lateral view; G, H. Pupa ♀, within an opened cocoon: G. Lateral view; H. Ventral view; I. Cocoon, lateral view. Scale bars: 5 mm.

Morphology. Head capsule is dark gray and sparse yellow powder is visible in some individuals, with yellowish adfrontal area, and labrum and basal antacoriae a pale yellow. The integumentary color of T1–A10 is mostly vivid yellow, transversely decorated with black, dotted stripes. In lateral view, T2 is the most swollen area dorsally. Legs T1–3 are speckled with black on the lateral regions, while prolegs A3–6 have a yellow ground color similar to the former. Caudal horn on middorsal A8 is black and strongly developed.

Biology. A total of ten mature caterpillars were collected from a Morus sp. (Moraceae) in the wild at the type locality, on 02.v.2022. They were sent to Cao in Beijing and reared successfully in captivity on Morus alba. Liu had observed an individual on Camptotheca acuminata (Nyssaceae) at Fugong County, Yunnan, 1221 m, on 28.v.2023. After being brought back for indoor observations, it did not continue to feed on this plant or accept mulberry, and it ultimately starved to death. The caudal horn usually points to the posterosuperior side at rest, but it will swing back and forth (from anterior to posterior sides, with unstable frequency and speed) when frightened and crawling. After feeding ended, mature larvae always left their host plants to pupate in a cocoon. The larvae of HT and PTs span their cocoons ca. 05–09.v.2022.

Pupae (Fig. 2G, H):

Morphology of male and female pupae. The exterior shell is translucent after sclerotization is completed, showing yellowish tissues inside. Melanin is primarily pigmenting the spiracles A2–8 of the pupal exuviae, then distributed internally around the spiracle T1, and also the areas of middorsal A1–7 and dorsolateral T1–3. The subterminal costal margins of forewings come in contact medioventrally; antennae, maxillae and legs T1–3 are clearly visible.

Biology. During development of the adult in the pupa, the proximal regions of antennae, of the lateral areas of compound eyes, off the tarsi of legs T1 and of the tip of A10 become pigmented blackish earlier than other structures.

Cocoons (Fig. 2G–I):

Morphology. White ellipsoid in general, about twice as long as wide, with the pupa nested inside along its longitudinal axis. The outer fibers form a wrinkled, irregular layer, that appears as a loose and perforated filament-layer in horizontal section. The innermost [pupal chamber] surface of the cocoon is regular and relatively smooth.

Imagines (Figs 1, 2A–D):

Morphology of males. Head largely covered by black scales, but the frontoclypeal area is off-white, with black compound eyes and bipectinate antennae. The labial palpus is but vestigial and very minute. The white scales are distributed on the subdorsal areas T2–A8, the subventral areas A2–8 and the tip of A9. The abdominal venter is grayish, while other areas of the whole body bear black scales; especially on T1 and tegulae, these scales are longish and hair-like. Legs T1–3 are also darkly colored, and the longest hair-like scales are located on the lateral margins of tibiae and basitarsi of forelegs. Both fore- and hindwings are semitransparent, the lengths are ca. 2.2 cm (from the wing base to the tip of R4, HT) and ca. 1.8 cm, (from the wing base to the tip of CuA1, HT), respectively. Viewed from both dorsal and ventral sides, each wing-vein is located within a gray-black scaly stripe, such bands likewise decorated on the postbasal (only forewings), median (all wings), marginal (all wings, and here including costa-apex-termen-inners) areas, while other regions have a light cover with white scales. The termen of the hindwing is slightly concave around the tip of 1A.

The sternum A8 is caudally digitiform and directed toward the posterior side, carrying dorsolateral bristles. Amongst the genital structures, tegumen and vinculum are fused and form a narrowly elliptic ring, with the vinculum extending into a very short saccus. The uncus is deeply bilobed, laterally sclerotized and medially membranous, its wedge-shaped terminal is inferolaterally setose. A pair of cambered sclerites derived from the gnathos is strongly developed, linked with the uncus by lateral membrane. The narrow and crescent valva is expanding terminally which ended with a rounded and smooth dorsodistal margin, each cucullus has serrated inferior margin with two or three identifiable pointed teeth bearing medioventral corona. The juxta is V-shaped and slightly protruding. The phallus is thin, long and straight, with a pointed tip that has a slightly helical opening; the caecum penis is well developed.

Morphology of females. Color pattern is nearly identical to males,but females are usually larger in size than males. Visually, wings appear narrower, longer and paler than in males, with lengths of forewing ca. 2.4 cm (from the wing base to the tip of R4, PT [A23072706]) and hindwing ca. 1.9 cm, (from the wing base to the tip of CuA1, PT [A23072706]). Prior to oviposition, A2–7 medioventrally covered by many long, black scales.

Biology. Adults HT and PTs emerged from cocoons between 14 and 18.v.2022. In resting position, moths usually hold their forewings with their costal margins horizontal (perpendicular to the body), while the anal angles of the hindwings are widely separated from each other (Fig. 2D). There was no successful pairing in captivity, but adults were found to be active during the day. Unfertile females nonetheless laid eggs, covering them with black scales from their abdominal midventral areas. It is noteworthy that the dorsal epicuticle of the membranous areas of wings appeared slightly iridescent while moths were alive, which was difficult to observe in dead, dry specimens.

Distribution

The specimens in this study are all from Leshan (Sichuan) and Fugong (Yunnan), but the new species may be more widely distributed in montane broadleaf forests in both provinces. However, due to the presence of similar environments, we presume the species may also be found in the northern Indochina Peninsula, e.g., in Myanmar, Laos, and Vietnam.

Diagnosis

Adults of R. melanoleuca sp. nov. have wings with distinct white patches placed between black vertical stripes and black wing-veins, which enables easy distinction from all other bombycids without dissection of genital structures. Wang et al. (2015) provided a diagnosis for R. menciana, R. diaphana and R. lineata, in which they noted “forewing with outer margin concave below apex and a projection at the end of M3 […] uncus divided into three lobes; valval apex broader with a large and a small tooth”. In contrast, the new species has a straighter forewing termen, a biforked uncus, and a rounded dorsodistal edge of the valva.

Etymology

This feminine adjective in modern Latin means “black and white”; interestingly, the Sichuanese giant panda carries the same specific name.

Molecular phylogeny

The phylogenetic tree (Fig. 3) reveals that R. melanoleuca sp. nov. is sister to R. menciana + R. diaphana, with a high support value of 99%. The generic relationships revealed by the topology obtained are in agreement with Wang et al. (2018) and Deng et al. (2022).

Figure 3. 

ML tree of the family Bombycidae (part) based on COI dataset, the outgroup (Saturniidae) is not shown. The scale bar indicates average substitutions per site. The nodal support is indicated by ultrafast bootstrap values.

Discussion and conclusion

This study introduces a very distinct new species with many unique phenotypic characteristics. The wing pattern in particular is completely different from the hypothetical ground plan of all other bombycines. However, we observe that the general morphology of the mature larva of R. melanoleuca sp. nov. is relatively similar to that of other known species of Rondotia, even though differences can be highlighted: R. menciana and R. diaphana (Anonymous 2020) mature larvae are whitish, covered with a distinct white powder, and spin yellow cocoons attached to leaves of their host plants.

The results of our phylogenetic analysis based on sequences of the COI gene have revealed that R. melanoleuca sp. nov. is sister to a clade formed by R. menciana and R. diaphana (see Fig. 3). Considering the very high morphological similarity of R. lineata with these two species, it can be assumed that the new species is sister to all other Rondotia species. This assumption agrees with the morphological uniqueness of R. melanoleuca sp. nov. in comparison to the relative uniformity of all other species known to date in the genus. Interestingly, the new species looks superficially like the butterfly genus Aporia Hübner, 1819 (Pieridae), and future ecological studies would be needed to clarify if a mimetic relationship exists between R. melanoleuca sp. nov. and other Lepidoptera species.

Acknowledgments

We are grateful to Andreas Zwick (CSIRO, Canberra) for providing considerable advice that helped improve the scientific quality of this article, as well as the comments from an anonymous reviewer. We thank Rodolphe Rougerie (MNHN, Paris) for editing the manuscript, Fei Lu (Southwest Forestry University, Kunming) and Siyao Huang (LIB, Museum Koenig, Bonn) offered kind help and suggestions, respectively. A special thanks goes to the photographer Yongxiang Zhou (Kunming), who assisted in the photography of Fig. 1E–H.

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