Neglected pseudomuga silkmoth reveals ancient Himalayan origins

Deep in the rain-soaked montane forests along the southeastern edges of the Himalayas lives a giant silkmoth that has spent more than a century hiding in plain sight. Antheraea castanea, described by Karl Jordan in 1910 from the Khasi Hills of Meghalaya, casts chestnut-brown wings spanning more than ten centimeters, yet it has been so frequently confused with India’s famous muga silkmoth that many researchers treated it as little more than a synonym. Now, a team of Chinese entomologists has published the first complete life history of this neglected species, together with new mitochondrial genomes that reveal it occupies a far more important position in the evolutionary tree than anyone suspected.

The study, published in the Deutsche Entomologische Zeitschrift, reports that Antheraea castanea is the sister group to all other species within the subgenus Antheraeopsis, the clade that contains the economically vital muga silkmoth Antheraea assamensis. This phylogenetic placement strongly supports the hypothesis that the entire subgenus originated in the subtropical forests at the eastern end of the Himalayas, near the present range of A. castanea. The finding transforms what was once a footnote in saturniid taxonomy into a key taxon for understanding the evolutionary history of the genus Antheraea, one of the most species-rich and commercially significant groups of giant silkmoths in Asia.

To achieve this, the researchers collected six wild females from the borders of southeastern Yunnan and southeastern Tibet, at elevations between roughly 1,200 and 2,200 meters in the rain-rich broadleaf forests of Mêdog, Nujiang, Baoshan, Dehong, Pu’er, and Honghe. The eggs laid by these females were reared through five larval instars on specific host plants within the laurel family, Lauraceae, allowing the team to document every stage from ovum to adult for the first time. The resulting descriptions reveal a caterpillar of remarkable beauty, shifting through vivid yellow, yellowish-green, and deep green colorations adorned with bluish-purple, mulberry-colored, and finally vivid purple warts, with metallic silvery zones on the dorsal scoli that develop progressively through the later instars.

Scanning electron microscopy of the eggshell showed a tri-axial ellipsoid ovum measuring about 2.65 by 2.22 by 1.68 millimeters, with a grayish chorion covered in dark brown glue. The micropylar rosette is composed of polygonal imprints left by follicle cells, while crowned aeropyles are dispersed across the external surface except in and immediately around the micropylar zone. This distribution pattern aligns with what has been described for other Antheraeopsis species, including A. rubiginea and A. assamensis, providing yet another line of morphological evidence linking A. castanea to its relatives.

The rearing experiments also exposed a strikingly narrow dietary range. Larvae from Yunnan accepted only two laurel species, Litsea populifolia and Camphora septentrionale, rejecting every non-lauraceous plant offered, including Quercus yunnanensis, Alnus nepalensis, and Liquidambar formosana. Larvae from Tibet proved even more specialized, completing development exclusively on Litsea rubescens while failing to survive on Camphora. This strong oligophagous tendency on Lauraceae is now confirmed as an autapomorphy of the entire subgenus Antheraeopsis, distinguishing it sharply from the other two subgenera of Antheraea, which feed primarily on oaks and other non-lauraceous plants.

On the molecular front, the team sequenced two new complete mitochondrial genomes, one from a first-instar larva of A. castanea and one from an adult male of A. youngi, a Bornean species. The A. castanea mitochondrial genome spans 15,325 base pairs, while that of A. youngi spans 15,307 base pairs. Using these sequences together with data from 39 other saturniid species and appropriate outgroups, the researchers constructed phylogenetic trees using maximum likelihood inference under the best-fit model GTR + F + I + R5. The results show that the subgenus Antheraeopsis consists of three major species groups: an assamensis-group of four species distributed across mainland Southeast Asia, a youngi-group of five species occupying Sundaland and the Philippines, and a castanea-group containing the single species A. castanea as the sister to the other two clades combined.

A second analysis based on COI barcodes from ten Antheraeopsis species, downloaded from BOLD Systems, produced a fully congruent topology. All Antheraeopsis nodes received maximal support in the mitochondrial genome phylogeny, while certain nodes in the combined mitochondrial genome plus COI topology showed lower support, likely reflecting the incomplete COI sequences available for multiple species. The researchers note that future higher-quality genomic or more detailed morphological studies will help clarify finer phylogenetic details within each species group, including possible synonym relationships within the assamensis-group and the precise relationship between Palawan A. sahi and Bornean A. youngi.

Perhaps the most biologically intriguing result concerns the timing of divergence. Previous work by Rougerie and colleagues estimated that A. castanea and its sister group diverged approximately four million years ago. Given the current distribution of the crown group, the researchers infer that this speciation occurred in the subtropical forests at the eastern end of the Himalayas, near the present range of A. castanea, suggesting the subgeneric origin. Interestingly, the subgenus Telea may share a similar evolutionary history, with most of its species distributed in the New World and only one relict sub-Himalayan taxon, Antheraea compta, occupying a nearly identical habitat to A. castanea, though the latter feeds on oaks rather than laurels.

Despite its phylogenetic significance, A. castanea has long been neglected in sericulture, partly because adults and habitats overlap with those of the muga silkmoth. The researchers propose the common name pseudomuga, from the Greek pseudo meaning false, to help Asian entomologists distinguish it from the true muga and to encourage greater attention in future field sampling and breeding efforts. They recommend increased study of A. castanea particularly to prevent misidentification with A. assamensis, which shares similar montane laurel forests. The cocoons of A. castanea appear white in relatively dry indoor environments but oxidize to light brown when thoroughly wet, a pattern that mirrors the color variation seen in muga populations, though the researchers caution that valid data on silk protein components or microstructures are still lacking for meaningful comparison between Antheraeopsis species.

The complete life history now documented for A. castanea also reveals distinctive larval characters that separate it from all other known Antheraeopsis caterpillars. In the first instar, A. castanea has a shiny red-brown head capsule with an almost entirely black dorsum on the prothorax and no black markings on the prolegs, whereas all compared relatives exhibit a shiny black or blackish-brown head capsule with black transverse stripes and lateral black spots at the proleg bases. In later instars, the continuous dark green lateral stripe that Nässig identified as a subgeneric synapomorphy appears indistinct in A. castanea, and the Tibetan population uniquely develops shiny, clubbed setae on all major scoli during the fourth and fifth instars, a feature not observed in Yunnan larvae or any other described Antheraeopsis. These morphological differences, combined with the molecular evidence, firmly establish A. castanea as a lineage worthy of far more scientific attention than its century of obscurity has afforded it.

Subject of Research: Antheraea castanea

Article Title:  Antheraea castanea Jordan, 1910, the neglected "pseudomuga" silkmoth ( Lepidoptera , Saturniidae )

Article References: Liu, Z., Hu, C., & He, M. (2025). Antheraea castanea Jordan, 1910, the neglected "pseudomuga" silkmoth (Lepidoptera, Saturniidae). Deutsche Entomologische Zeitschrift, 72(2), 303-315. https://doi.org/10.3897/dez.72.151952

Image Credits: AI Generated

DOI: 10.3897/dez.72.151952

Keywords: Antheraea castanea, pseudomuga, silkmoth, Antheraeopsis, mitochondrial genome, phylogenetics, sericulture, Lauraceae, Antheraea, castanea, Jordan, neglected