First description of the third-stage larva and puparium of Brachyopa testacea (Fallén, 1817) (Diptera, Syrphidae), with a revised identification key for larvae of the European Brachyopa Meigen, 1822

The immature stages of Brachyopa testacea (Fallén, 1817), a saproxylic hoverfly with a wide range extending from western and central Europe through Scandinavia to the Asiatic parts of Russia, Mongolia and the Pacific, are described for the first time based on reared material from Denmark. The species is associated with Picea forests where adults are frequently encountered around recently felled stumps, making it one of the more regularly recorded Brachyopa species within suitable habitats.

The description is based on comprehensive morphological documentation, including chaetotaxy mapping, optical microscopy, and scanning electron microscopy. The identification key for European Brachyopa larvae has been revised and updated to incorporate B. testacea and to correct ambiguities in previous keys concerning Brachyopa panzeri Goffe, 1945 and Brachyopa dorsata Zetterstedt, 1837. The improved key addresses inconsistencies in morphological terminology and incorporates standardized chaetotaxy-based characters, enhancing the reliability of larval identification.

This study emphasizes the continuing need for comprehensive descriptions of Brachyopa species immature stages to facilitate biodiversity assessment, ecological research and conservation of these important forest habitat indicators.