DNA barcoding reveals a new cryptic species of Denisia Hübner, 1825 (Lepidoptera, Oecophoridae) from the south-western Alps

Deep in the nature parks of the Cottian Alps, where pine forests climb toward 1,700 metres above sea level, a small moth has been hiding in plain sight. It looks so much like its relatives that even seasoned lepidopterists misidentified specimens collected decades ago. Only when researchers ran its DNA through a barcode scanner of the genetic kind did the truth emerge: the insect belongs to an entirely new species, now formally named Denisia cryptica, a concealer moth from the family Oecophoridae that had never before been catalogued by science.

The discovery, published in the journal Alpine Entomology, is the work of Peter Huemer of the Tiroler Landesmuseum Ferdinandeum in Innsbruck, Austria, who has spent years surveying the Lepidoptera of the Cottian Alps in northwestern Italy. The new species was collected at light traps in June 2020 and 2022 within the Orsiera-Rocciavrè Nature Park in the province of Torino, and additional specimens turned out to have been sitting in collections from the French Alps since 1995 and 1998, misidentified as a superficially similar species. The name cryptica, derived from the Latin adjective crypticus, refers precisely to this hidden, cryptic appearance.

Denisia is one of the more species-rich genera of concealer moths in Europe, with 23 recorded species out of 139 European members of the family Oecophoridae. Remarkably, four of those 23 species were only discovered in the twenty-first century, a statistic that hints at how much biodiversity remains undocumented even on a well-studied continent. Only a handful of species, such as Denisia stipella and Denisia similella, are widely distributed across temperate Europe; the vast majority occupy localized ranges, and the great mountain systems of Europe, including the Pyrenees, the Alps and the Caucasus, harbour regional endemics found nowhere else.

What makes the new species so difficult to pin down is a combination of subtle external characters and, crucially, genitalia that look extremely like those of several other species in the genus. The male and female genitalia of Denisia cryptica differ from its closest relatives only in subtle features such as the length and shape of the uncus and valva in males, and the shape of the small thorn-edged signum in females. Traditionally, moth taxonomy has leaned heavily on these genital structures as the gold standard for species delimitation, but in Denisia that approach frequently reaches its limits.

The diagnostic characters that do separate the new species are a complex of colour and pattern traits. Denisia cryptica has a cream-yellow scaled head, and the second segment of its labial palpi is at least partially yellow on the inner side, a feature absent in the similar dark-headed species Denisia nubilosella and the North American Denisia haydenella, whose labial palps are grey-brown on the inner side with only a few whitish scales. The scapus, the basal segment of the antenna, is cream-yellow rather than grey-brown. The forewing upperside is grey-brown with extended cream-yellow mottling and intense yellow speckling, whereas Denisia stipella and Denisia similella, which do share the yellow head and palps, are immediately distinguishable by their striking yellow forewing patterns. Forewing length ranges from 7.4 to 7.6 millimetres in males and about 6.8 millimetres in the single available female.

The decisive evidence came from DNA barcoding, the technique of sequencing a standardized 658-base-pair segment of the mitochondrial cytochrome c oxidase subunit 1 gene, the COI barcode region that has become the workhorse of modern species identification. Tissue samples from a single hind leg of three specimens of the new species were processed at the Canadian Centre for DNA Barcoding at the University of Guelph using standard high-throughput protocols. The three sequences were then compared against 155 public and private barcode sequences of 19 species of Denisia held in the Barcode of Life Data Systems, BOLD, the international reference database maintained at the Biodiversity Institute of Ontario.

The results were unambiguous. The three sequences of Denisia cryptica formed a single unique cluster with zero intraspecific divergence, assigned to its own Barcode Index Number, an algorithm-based operational taxonomic unit that serves as an accurate proxy for true species. The distance to the nearest neighbour, the North American Denisia haydenella, was 4.9 percent, well within the range of interspecific divergence typical of the genus. Across the molecular analysis, interspecific distances to the nearest neighbour varied from 4.3 to 9.3 percent per species pair, with only one alleged case of barcode sharing, the European species pair Denisia pyrenaica and Denisia graslinella, which may possibly reflect a previously overlooked synonymy. Intraspecific variation was generally much lower, with a maximum of 1.5 percent in most species, although it exceeds 4 percent in three species whose taxonomic revisions are still pending.

The analysis grouped the sequenced material into 23 distinct and strongly divergent clusters, each with different Barcode Index Numbers. A Neighbor-Joining tree constructed with the Kimura two-parameter model confirmed the pattern: nearly every species of Denisia exhibits significant genetic divergence on the order of roughly 4 to 9 percent, a level the authors consider highly representative for the genus given the large number of sequenced taxa. In total, 224 phenotypically similar specimens were examined morphologically, including 133 Denisia stipella, 37 Denisia similella, 23 Denisia fuscicapitella, 22 Denisia nubilosella, and small numbers of species from Spain, Finland and Russia, all preserved in the research collection of the Tiroler Landesmuseum Ferdinandeum.

Almost nothing is known about the biology of the new species. Adults were collected in June at light, and the host plant and early stages remain unknown. However, like related species, it possibly feeds under the bark of decaying or dead trees, and from the habitat at the type locality, Scots pine, Pinus sylvestris, is considered the most likely candidate host. By contrast, the superficially similar Denisia nubilosella appears restricted to Norway spruce, Picea abies. The genus as a whole shows two trophic strategies: a large group of species lives on dead wood, while another, demonstrated for the alpine endemic Denisia rhaetica, feeds on lichens growing on rocks, meaning typical habitats encompass both forest environments and rocky terrain extending into the alpine zone.

Currently Denisia cryptica is known only from two localities in the northern Cottian Alps of Italy and two isolated spots in the French Alps, at elevations between roughly 1,445 and 1,900 metres, but the authors consider it likely more widely distributed. The French specimens had been misidentified as Denisia nubilosella, and the occurrence of that species in the south-western Alps now requires confirmation. The discovery may come as a surprise at first glance, but the Southern Alps exhibit a particularly high degree of endemism, and the Cottian Alps have long been recognized as a hotspot for endemic Lepidoptera, with several new species described from there even in the twenty-first century. The systematic application of molecular methods to extensive newly collected material suggests an astonishingly large number of additional, previously overlooked cryptic species still await discovery.

To put the new species in context, the paper also provides a complete checklist of the European species of Denisia, tracing the genus and its many synonyms back to the type species Phalaena (Tinea) stipella Linnaeus, 1758. The systematic arrangement follows current European references and is based mainly on superficial morphological resemblance of wing pattern and genitalia structures, but the authors note that the generic delimitation of Denisia and related genera requires further investigation, particularly through extensive molecular analyses, not least because a recent synonymization of a North American species reflects the general lack of a phylogenetic analysis of the subfamily Oecophorinae.

For now, the message of the new species is clear. Even in the densely populated heart of Europe, in the mountains between Italy and France, a moth can live for centuries unrecognized, collected at light traps by naturalists and filed away under the wrong name, waiting for a few hundred base pairs of mitochondrial DNA to reveal its true identity. As DNA barcoding is applied ever more rigorously to museum drawers and fresh collections alike, the hidden diversity of the Alps, and of the world, is steadily coming into focus, one cryptic species at a time.

Subject of Research: DNA barcoding reveals a new cryptic species of Denisia Hübner, 1825 (Lepidoptera, Oecophoridae) from the south-western Alps

Article Title: DNA barcoding reveals a new cryptic species of Denisia Hübner, 1825 ( Lepidoptera , Oecophoridae ) from the south-western Alps

Article References: Huemer, P. (2024). DNA barcoding reveals a new cryptic species of Denisia Hübner, 1825 (Lepidoptera, Oecophoridae) from the south-western Alps. Alpine Entomology, 8, 121-130. https://doi.org/10.3897/alpento.8.127794

Image Credits: AI Generated

DOI: 10.3897/alpento.8.127794

Keywords: barcoding, reveals, cryptic, species, Denisia, bner, Lepidoptera, Oecophoridae, south-western, Alps, scientific research