DNA sequences from three successfully analyzed wasps supported their assignment to a single species. The researchers also reported new European records of three previously described congeners and produced an identification key for both sexes of the genus’s described European species. The study examined the naming and recognition problems affecting Cleruchus , a cosmopolitan genus of parasitoid wasps in the family Mymaridae.

Members of the genus are minute, inconspicuous and often collected from concealed habitats, including soil, leaf litter, bracket fungi and other small microhabitats. Some species are also frequently brachypterous, meaning that they possess shortened wings, while others may be apterous and lack functional wings. Reduced-wing forms can differ markedly from fully winged members of the same species in size, antennal structure, ocelli and the number of sensory structures, or multiporous plate sensilla, on the female antenna.

These differences can make specimens from one biological species appear to represent separate taxa, particularly when identification relies on morphology alone. Samples of Antrodia xantha infested with Cis chinensis were collected on three days—June 27, June 28 and July 11, 2021—from a block of Pinus strobus in the therapy garden of the University Psychiatric Clinics campus in Basel. A large series of unidentified mymarid wasps was observed almost entirely in the June 27 sample, with living wasps appearing between July 8 and July 26.

Coray preserved specimens in 90% and 75% ethanol before they were shipped for mounting, determination, DNA analysis and formal description. Additional unidentified Cleruchus specimens from other European countries were also examined, providing material for documenting range extensions and assessing variation within the genus. Because the wasps are so small, the researchers dissected them and mounted them directly from ethanol on slides in Canada balsam.

The preparations were examined with a Zeiss Axioskop 2 plus compound microscope and photographed using an Auto-Montage system, with some images retouched for presentation. Measurements generally were reported in micrometres, except body length, which was given in millimetres, while wing measurements were expressed as length or length-to-width ratios. The authors followed established morphological terminology and used body proportions, antennal form, sensory structures, wing venation, setae, ocelli and genital structures to assess the specimens.

The selected macropterous female holotype measured 665 micrometres in body length, including a 370-micrometre gaster and a 376-micrometre fore wing. Its antennal clava was only 82 micrometres long, providing the basis for the species name breviclava . Among fully winged females, C. breviclava was considered most similar to the Palearctic species Cleruchus detritus , but the authors identified several distinctions.

The female antennal clava of C. breviclava was consistently relatively shorter than in C. detritus , whose clava was approximately as long as the combined length of antennal segments F3–F6. Slide-mounted, fully winged females of C. breviclava had body lengths of 0.60–0.76 millimetres, whereas the described C. detritus female measured about 0.45 millimetre. The new species also had a markedly longer gaster, notably shorter setae along the fore-wing venation and a different recorded habitat.

C. detritus was originally collected from soil, while C. breviclava was reared from a fungus. The authors regarded this combination of proportional, structural and ecological differences as strong evidence that the two species are distinct. Variation within the newly reared species was substantial.

Fully winged females measured 600–760 micrometres, had antennal clavae 2.6–2.8 times as long as wide and had fore wings 8.6–9.5 times as long as wide. The strongly brachypterous female measured 515 micrometres, possessed more reduced ocelli, a relatively shorter antenna and fewer antennal sensilla. Its fore wing was reduced to a tiny setose stub, and no hind wing was apparent.

The strongly brachypterous male measured 470 micrometres, apparently lacked ocelli and had a nine-segmented antennal flagellum, with F3 and F4 completely fused on one antenna and partially fused on the other. Fully winged males measured approximately 585–590 micrometres, retained ocelli and had ten flagellomeres. In both sexes, therefore, the same rearing event produced forms differing in structures commonly used for species identification.

The molecular analysis supplied the principal evidence that the morphologically divergent wasps were conspecific. DNA was extracted from four individuals: one fully winged female, one strongly short-winged female, one fully winged male and one strongly short-winged male. Three produced amplifiable DNA.

Their 502-base-pair mitochondrial cytochrome c oxidase subunit I sequences and 519-base-pair 28S-D2 nuclear ribosomal RNA sequences were identical across all three specimens. ITS2 sequences from the two analyzed males differed at only one nucleotide position. The authors therefore considered the near-identity across all three loci unambiguous evidence that the fully winged female, fully winged male and strongly brachypterous male belonged together.

The fourth specimen, a strongly brachypterous female whose extraction apparently failed, was assigned to the same species on the basis of its morphology and its emergence from the same fungus. The comparison could not be extended to determine the species’ relationship with other identified Cleruchus taxa because the authors found no DNA sequences from positively identified congeners in GenBank or BOLD. A Basel COI sequence was 97.6% similar to an unidentified female Cleruchus from nearby Grenzach-Wyhlen, Germany, whose digital image was also morphologically similar.

That German specimen had been collected from Stereum fungus containing native Cis beetles. Additional observations of C. breviclava in low mountains in Germany and Switzerland had previously been reported only as unidentified Cleruchus . The study consequently listed Switzerland and Germany as its known Palearctic distribution and documented C. chinensis in A. xantha on P. strobus as its host association.

It was the first application of an integrative taxonomic approach to Cleruchus , although comparable genetic data were not yet available for other positively identified members of the genus. The paper also expanded the documented distributions of three other Cleruchus species. Cleruchus megatrichus was recorded from a citrus orchard in Valencia, Spain, joining earlier records from Finland, France and Poland.

Cleruchus szelenyi was newly reported from Germany and the Netherlands; examined specimens came from pitfall traps in an apple orchard in Rhineland-Palatinate and grassland in Gelderland. Cleruchus taktochno was newly recorded from the Netherlands on the basis of a fully winged male collected in grassland. These observations illustrate the value of targeted trap sampling, because yellow pans, flight-interception and pitfall traps, as well as soil and litter extractors, may recover fairyflies that are seldom encountered by sweeping or Malaise traps.

The authors emphasized that the true number of valid European Cleruchus species remains uncertain, both because undescribed species may exist and because some wingless nominal species could prove synonymous with taxa currently known only from fully winged specimens. Several taxonomic uncertainties remain beyond the newly described species. The original syntypes of C. detritus included both apterous and fully winged females recovered by washing soil at the same locality, a method capable of combining individuals from more than one species.

The apterous forms had previously been treated as C. szelenyi , and their possible conspecificity with the fully winged C. detritus cannot be resolved from morphology alone. The authors called for genetic study of newly collected fully winged and apterous material from the C. detritus type locality, followed by comparison with C. breviclava and C. szelenyi . They also noted that the small size, concealed habitats, substantial within-species variation and reduction or fusion of antennal segments in wingless males continue to impede recognition of the genus.

The study therefore resolves the identity of the Basel rearing series while demonstrating why DNA libraries and combined morphological and molecular evidence are needed to describe Europe’s still incompletely catalogued fairyfly diversity.

Subject of Research: Integrative taxonomy of the parasitoid fairyfly Cleruchus breviclava and its European congeners

Article Title: A new species of Cleruchus ( Hymenoptera , Mymaridae ), an egg parasitoid of the invasive Cis chinensis ( Coleoptera , Ciidae ) in Switzerland, with new records of other congeners in Europe

Article References: Triapitsyn, S. V., Coray, A., & Rugman-Jones, P. F. (2022). A new species of Cleruchus (Hymenoptera, Mymaridae), an egg parasitoid of the invasive Cis chinensis (Coleoptera, Ciidae) in Switzerland, with new records of other congeners in Europe. Alpine Entomology, 6, 97-109. https://doi.org/10.3897/alpento.6.86806

Image Credits: AI Generated

DOI: 10.3897/alpento.6.86806

Keywords: Cleruchus breviclava, Mymaridae, fairyflies, egg parasitoids, Cis chinensis, integrative taxonomy, DNA barcoding, brachyptery, European biodiversity, fungus-associated wasps, species, Cleruchus