We celebrate Raymond J. Gagné for his contributions to taxonomy of the Mycetophilidae (Diptera), specifically for his forty-one-years-old monograph of Holarctic Trichonta Winnertz, 1864 that is still the primary source used for species identification in the genus. We briefly reflect on his monograph's impact and demonstrate by use of recent DNA barcode data extracted from BOLD Systems (BOLD) that the model for the distribution of Holarctic Mycetophilidae that Gagné presented in the monograph still holds up to scrutiny. To demonstrate the refined species concept now being applied by use of an integrative taxonomic approach that includes DNA barcodes, we revise a small, but distinct, species complex that Gagné recognized as one morphologically defined species and used as an example of an old pan-Holarctic taxon, Trichonta vulcani (Dziedzicki, 1889). We find the Trichonta vulcani species complex (sensu Kallweit 1998) to consist of at least six species in the Holarctic Region of which three are being described as new to science: Trichonta japonica Kurina, new species (East Palearctic), Trichonta neovulcani Kjaerandsen, new species (East Nearctic), Trichonta raymondgagnei Kjaerandsen, new species (Holarctic), Trichonta trifida Lundstrom, 1909 (wide Palearctic), Trichonta tristis (Strobl, 1898) (wide Palearctic), and Trichonta vulcani (Dziedzicki, 1889) (wide Palearctic). All six species are distinctly separated by DNA barcodes that correspond well to minor, but constant, differences in their male terminalia. However, one of the widespread species, Trichonta trifida, displays some genetic and morphological differentiation between western and eastern Palaearctic populations. We presently consider these populations conspecific pending broader sampling. We further propose a replacement name Trichonta nepalensis Kjaerandsen, new name for Trichonta superba Gagné, 1981, a junior primary homonym of Trichonta superba Ostroverkhova, 1979, the latter being a junior secondary synonym of Trichonta tristis (Strobl, 1898).