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A tiny fly collected in an oak-and-chestnut forest near Losone, in the Swiss canton of Ticino, has been identified as a species new to science. It is called Periscelis (Myodris) haennii. The discovery came during a survey of forest insects. Many of the flies looked like Periscelis (M.) annulata when researchers used an existing identification guide, but the males had different genital structures. The researchers studied these new specimens alongside the other two European species in the subgenus Myodris, described the male genital structures of P. (M.) annulata in greater detail, and used DNA barcoding to test whether the species were different.
The study identifies P. (M.) haennii as a cryptic species. This means it looks so much like closely related species that its identity cannot be reliably determined from its external appearance alone. The research was part of an insect study run by the Natural History Museum of Canton Ticino in Lugano to record the variety of insects living in forests around Locarno. Researchers studied three sites in an oak-and-chestnut forest over one full year, from July 2015 to July 2016, using several kinds of traps.
Three slightly different baited traps caught 99.4% of all the collected Periscelididae flies. Two traps were transparent and contained wine or beer, while the third was yellow and contained wine. The researchers caught 305 males of the new species. They first preserved the specimens in ethanol. Then they dried 53 specimens, selected as the type series, and mounted them on pins so they could study them closely.
According to the most recent identification guide available to the researchers at the time, many of the captured flies were classified as P. (M.) annulata, a species first described by Fallén in 1813. However, the male genital structures did not match the features used to identify that species. This difference led the researchers to seek expert help with the classification from the late László Papp of Budapest and Miguel Carles-Tolrá of Barcelona.
To find out whether the unusual genital structures belonged to a separate species, the team examined the male genital structures of all three European members of Myodris: P. (M.) haennii, P. (M.) annulata, and P. (M.) piricercus, which Carles-Tolrá and Verdugo Páez described in 2009. As part of this comparison, the researchers described and illustrated the male genital structures of P. (M.) annulata in greater detail. The type specimen, called the holotype, of the new species has a total body length of 1.31 mm and a wing length of 1.01 mm.
The fly is mainly brown and grey, with dull surfaces covered in a very fine, powder-like coating. Parts of its head, mouthparts, and legs are yellow to yellow-ochre. The fine coating on the scutum and scutellum, two parts of the thorax, is darker and browner than in P. (M.) annulata. As a result, the brown stripes along the middle and sides of the thorax stand out less clearly from the surrounding color. The legs are yellow and brown. Small silvery-white spots appear along the outer edges of abdominal segments 3–6.
Some of these external features differ from those of P. (M.) annulata, but the most important differences are in the male genital structures, especially the cerci, surstylus, postgonite, and ejacapodeme. In the new species, the cerci are longer and thinner than those of P. (M.) annulata, and they are longer than the anal opening in the epandrium. Each cercus has two short, thick spines near its front tip. The spines grow close together. The hairs near the rear edge, just before the tip, are only slightly longer than the nearby hairs along the rear edge.
The surstylus becomes narrower more gradually and stays fairly straight near its tip. The postgonite is longer overall, with a thin end section that is longer and slightly bent. The ejacapodeme is also longer in proportion to its width. It is about 5.5 times as long as its widest point, compared with about 4.5 times as long in P. (M.) annulata.
These differences form the basis of the researchers' identification guide for male Myodris flies found in Europe. DNA analysis provided another way to check the results. The researchers copied and sequenced the COI DNA barcoding region from one specimen each of P. (M.) haennii, P. (M.) annulata, and P. (M.) piricercus. They also analyzed Periscelis (s. str.) winnertzii for comparison.
All the flies analyzed came from Losone in Ticino and had been preserved in 80% ethanol. Each COI DNA sequence was 658 base pairs long. The researchers calculated genetic differences using the Kimura two-parameter model. P. (M.) haennii differed genetically from P. (M.) annulata by 7.58% and from P. (M.) piricercus by 9.12%.
The genetic difference between P. (M.) annulata and P. (M.) piricercus was 6.88%. Because the researchers analyzed only one specimen of each species, they could not measure genetic variation within each species. Studying many specimens of all three European Myodris species from the same place and habitat also revealed variation that had not been recognized before. This included differences in the fine hairs on the thorax, body color patterns, and dark or cloudy areas on the wings and wing veins.
The dark markings on the wings varied especially widely in P. (M.) annulata. The researchers therefore concluded that the three species cannot be identified reliably using external features alone. Their identity should always be checked by examining the male genital structures. For now, females cannot be assigned confidently to a species based on their physical features, although the study reports that DNA barcoding can identify them.
The new identification guide therefore covers only males and relies on genital structures rather than the variable body colors and wing patterns found in the collected flies. In the guide, P. (M.) piricercus is separated from the other two species by several features: it has fewer hairs on the pregenital sternum, a short, pear-shaped cercus with a wider base, a short surstylus with a broad base, and a short, wide postgonite with a thick tip. Both P. (M.) haennii and P. (M.) annulata have more hairs on their pregenital sternites, long and slender cerci, long and slender surstyli, and long postgonites that become thinner toward their tips.
The new species differs from P. (M.) annulata in the relative length of its cercus, the close spacing of the two spines near the front tip of the cercus, the less noticeable hairs near the rear of the cercus, the straighter end of the surstylus, and the longer, slightly bent end of the postgonite. Researchers use these specific features under magnification to tell the two species apart. The type locality is the Forest Reserve of Parco Collina di Maia in Losone, at 46°09′53″ N, 8°44′54″ E and 419 metres above sea level.
The holotype is a male fly mounted on a pin. It was collected between 21 and 28 July 2015 in a chestnut-and-oak forest and is kept at the Natural History Museum of Canton Ticino. Other specimens in the type series, called paratypes, are held in Lugano and at the Silesian Museum in Opava, Czech Republic. Researchers also collected additional specimens in 2016 and 2017.
So far, P. (M.) haennii has been found only in southern Switzerland. The authors suggest that it may also live elsewhere in Europe, especially in southern areas. Earlier records identified as P. (M.) annulata may have included this newly discovered species. However, no confirmed records from outside Ticino have been reported. The biology of P. (M.) haennii is still unknown.
The authors think it is possible that the new species has habits similar to those of P. (M.) annulata. That species has been found around sap flowing from damaged trees, especially oaks and elms, often high in their branches. Reports also suggest that its larvae develop in fermenting tree sap. However, this is only a tentative comparison and does not establish the biology of the new species. What the researchers directly observed is that they caught 305 specimens in traps baited with wine and beer in a lowland forest mainly made up of oak and chestnut trees.
The same traps also caught both of the other European Myodris species and two species belonging to Periscelis in the strict sense. The authors describe P. (M.) haennii as another cryptic species in the family Periscelididae. They suggest that more unnamed species may be discovered, especially in eastern and southeastern parts of Europe that have not been studied as thoroughly, if researchers carry out long-term field studies and detailed examinations by taxonomic specialists.
Subject of Research: Identifying a new cryptic fly species in the family Periscelididae by studying male genital structures and COI DNA barcoding
Article Title: Periscelis ( Myodris ) haennii sp. nov., a new species of Periscelididae ( Diptera ) from Ticino, Switzerland, with a new key to European species of the subgenus
Article References: Pollini Paltrinieri, L., & Roháček, J. (2022). Periscelis (Myodris) haennii sp. nov., a new species of Periscelididae (Diptera) from Ticino, Switzerland, with a new key to European species of the subgenus. Alpine Entomology, 6, 39-49. https://doi.org/10.3897/alpento.6.85391
Image Credits: AI Generated
Keywords: new species, Periscelis haennii, Periscelididae, cryptic species, DNA barcoding, male genitalia, Myodris, Ticino, forest biodiversity, taxonomy, Periscelis, haennii