Fifty-Year-Old Alpine Insect Survey Rewritten by Modern Taxonomy

In a subalpine valley high in the French Pyrenees, a team of aquatic entomologists has just completed a painstaking re-examination of a stream survey first carried out more than fifty years ago, and the results reveal how much of biodiversity science rests on the shifting sands of species names. The original study, conducted by Pierre Lavandier between 1971 and 1973, catalogued the mayflies, stoneflies and caddisflies of the Estaragne catchment, a small stream system that rises at 2,600 metres in the Pyrenees National Park and flows into Orédon Lake without any glacial influence. When the researchers resampled the same twelve stream sites in 2022, using three seasonal campaigns and both larval and adult collections, they found that taxonomy itself had changed almost as much as the insects might have.

The core problem the team set out to solve is one that haunts every long-term ecological survey: a species name assigned to an organism is not an objective fact but a well-reasoned scientific hypothesis, subject to revision as methods and knowledge evolve. Species concepts are still debated, and the name a taxonomist gives to a specimen depends on the morphological, molecular or behavioural tools available at a particular moment in history. When researchers compare inventories separated by decades, differences in naming can masquerade as differences in nature. To guard against this, the team first updated Lavandier’s original list using current taxonomic knowledge before attempting any comparison with their own 2022 data.

The scale of the correction is striking. Of the 55 taxa of Ephemeroptera, Plecoptera and Trichoptera that Lavandier validated across his twelve sites, only 64 percent retained an unchanged taxonomic status. The remaining 36 percent required modifications: 70 percent were reassigned to different names, 15 percent were revised, and 15 percent were reduced to a higher taxonomic level such as a genus. Among the specific corrections, the mayfly once recorded as Baetis cf. niger turned out to be Alainites muticus, a morphologically similar species that genuinely inhabits high Pyrenean altitudes, while the stonefly listed as Nemoura erratica should instead be Nemoura pseudoerratica, a species only described in 2003 that had previously been confused with its relative.

Some corrections traced back to outright historical errors. The caddisfly larvae that Lavandier recorded as Micrasema morosum were reassigned to Micrasema vestitum, a Pyrenean endemic, after the team combined morphological examination of adults and pupae with DNA barcoding. Their analysis showed that larval descriptions published in 1970 had been misattributed across several Micrasema species, meaning the historical identification literature itself contained errors that propagated through decades of surveys. Similarly, the stonefly recorded as Arcynopteryx compacta was corrected to Arcynopteryx dichroa, resolving a century-old mistake in which an illustration of one species had been used to define the type of a genus.

The 2022 sampling itself was designed to maximise species detection rather than replicate Lavandier’s quantitative effort, which the team judged impossible to reproduce given the heterogeneity of his methods and the loss of his raw data and specimens. Two experienced operators spent an hour at each site on each visit, searching for larvae, nymphs, pupae, exuviae and winged adults along both riverbanks, supplemented by sweep netting of riparian vegetation. They visited every site in June, July and September, timed to the summer-autumn emergence that dominates high mountain EPT fauna. Challenging identifications were cross-validated by external specialists, and molecular analyses barcoded unreferenced species and tested uncertain affiliations, generating 180 accession numbers across nine mayfly, 24 stonefly and 32 caddisfly taxa.

In total, the 2022 inventory validated 80 taxa across the twelve sites, comprising 14 mayflies, 31 stoneflies and 35 caddisflies, though the authors caution that several affiliations may still shift as knowledge advances. The comparison between eras required further pruning: because several Pyrenean species from the Baetis alpinus and Baetis rhodani groups, along with four Rhithrogena species, were described only after 1979, the team retained only genus-level records for these groups in both datasets. After these adjustments, 70 taxa from 2022 could be compared against the 55 updated taxa from the 1970s.

The study also introduced a rigorous method for assessing species autochthony, meaning whether a species actually completes its entire life cycle at a given site rather than simply turning up as a dispersing adult. Adults captured on riverbanks may have flown in from upstream, downstream or even distant streams. Under the new protocol, a mayfly or stonefly counts as autochthonous only if identifiable larvae were collected, or, for genera such as Leuctra whose larvae cannot be reliably identified, if both an adult male and female were found alongside genus-level larvae. Caddisflies, whose adults disperse more widely, required larvae or pupae. Applying this framework, 70 of the 80 taxa recorded in 2022 were autochthonous to at least one site, and 317 of 392 taxon-site records were validated, giving future distribution studies a far more defensible baseline.

Molecular work exposed how much taxonomic uncertainty still hides within apparently well-studied groups. Sequencing revealed that the Pyrenean populations of the mayfly Rhithrogena loyolaea differ genetically from alpine populations, that the stonefly Leuctra rauscheri carries a haplotype distinct from other known European populations, and that the mayfly Baetis alpinus in Estaragne resembles Pyrenean rather than alpine haplotypes, all findings requiring further study to clarify species boundaries. Two Rhithrogena morphotypes, one from the hybrida group and one from the semicolorata group, appear to be undescribed species, the latter matching no known sequence in genetic databases. The stoneflies Isoperla moselyi and Isoperla viridinervis were treated as species complexes pending future investigation, and Perlodes specimens were conservatively labelled cf. intricatus and cf. microcephalus because their morphology and genetics diverge from topotypical alpine material.

The molecular gaps are particularly acute for endemic fauna. Of the 33 species endemic to the Pyrenees, the northern Iberian Peninsula and the Massif central that were collected in 2022, only 21 percent had at least one COI barcode sequence in the NCBI database at the time of identification. This scarcity of reference sequences for French EPT species, especially endemics, limits molecular and phylogenetic analyses and prompted the authors to call for a French barcode of life for these orders. They also advocate preserving reference specimens from every life stage, documenting species autochthony in inventories, and producing FAIR-compliant taxonomic datasets that record complete sampling metadata and the bibliographic references used for morphological identification, so that future researchers can re-evaluate assignments as knowledge evolves.

The broader lesson reaches well beyond one Pyrenean valley. The three insect orders studied here are among the most widely surveyed aquatic invertebrates in Europe and serve as standard bioindicators of environmental health, yet even they harbour undescribed species, cryptic lineages and larvae that cannot be identified at all with current knowledge. In France, national identification literature is either outdated or nonexistent, forcing ecologists to assemble references from neighbouring countries. The authors argue that long-term ecological surveys critically depend on transparent and revisable taxonomy, and that an ideal EPT inventory in high mountains should span at least two years with a minimum of four campaigns annually for mayflies and stoneflies and preferably five for caddisflies. The evolution of species distributions over the past fifty years will be analysed separately in a future study, but this work makes clear that any such comparison is only as reliable as the names attached to the specimens.

Subject of Research: Taxonomic revision of a 50-year-old aquatic insect survey in the French Pyrenees

Article Title: Revisiting a 50-year-old ecological study of Ephemeroptera , Plecoptera , and Trichoptera species in Estaragne River (French Pyrenees): why taxonomy matters?

Article References: Launay, B., Barnasson, J., Forcellini, M., Dangles, O., Moret, P., & Cauvy-Fraunié, S. (2026). Revisiting a 50-year-old ecological study of Ephemeroptera, Plecoptera, and Trichoptera species in Estaragne River (French Pyrenees): why taxonomy matters?. Alpine Entomology, 10, 195-226. https://doi.org/10.3897/alpento.10.204707

Image Credits: AI Generated

DOI: 10.3897/alpento.10.204707

Keywords: taxonomy, Ephemeroptera, Plecoptera, Trichoptera, long-term ecological survey, French Pyrenees, species inventory, DNA barcoding, autochthony, biodiversity, endemic species, aquatic insects