First description of the immature stages of the uncommon Triglyphus Loew 1840 hoverflies (Diptera Syrphidae)

With 10 species described, Triglyphus Loew 1840 is a rarely recorded genus of hoverflies (Diptera Syrphidae) from the Holarctic and Australian Regions. The biology of Triglyphus larvae is practically unknown as the only information available is that they prey on aphids in galls on Artemisia vulgaris L. (Asteraceae). We here report the first morphological description of the immature stages of a Triglyphus species and confirm their breeding site. Adults of Triglyphus primus Loew 1840 can be found in forests fringes, gardens, and on open grounds in the Palaearctic Region. Larvae of T. primus were collected preying on the aphid Cryptosiphum artemisiae Buckton 1879 (Hemiptera Aphididae) in galls on A. vulgaris in Denmark, in 2023. The first (L1) and the third (L3) larval instars, the puparium, head skeleton, and posterior respiratory process (PRP) were studied and analysed by using stereomicroscopic and scanning electron microscope (SEM) techniques. The chaetotaxy of the L3 and the types of sensilla are also described and illustrated. A taxonomic diagnosis of the larvae of Triglyphus is proposed to distinguish it from larvae of other syrphid genera by using the labrum shape in the head skeleton.