Comparative morphology of the first instar of three species of Metopia Meigen (Diptera: Sarcophagidae, Miltogramminae)

The first instar larva is described for three species of the kleptoparasitic miltogrammine genus Metopia Meigen: M. campestris (Fallén), M. argentata Macquart and M. argyrocephala (Meigen). Using a combination of light microscopy and scanning electron microscopy, the morphology of the cephaloskeleton as well as the general external morphology are extensively documented, and the phylogenetic implications are discussed. Like other species of Miltogramminae, the first instar of species of Metopia possesses a strong labrum and well‐developed mouth‐hooks. Some other features found in Metopia spp. are rare in the Miltogramminae, such as a serrated ventral surface of the tip of the mouth‐hook and the lack of a posterior spiracular cavity. A few larval features apparently unique for species of Metopia have so far been documented: base of mouth‐hook with a lateral arm‐like extension and abdominal segments with transverse furrow ventrally. The body is equipped with longitudinal cuticular ridges on all segments, which may be a subfamily ground‐plan autapomorphy. Marked morphological and behavioural differences are documented between the first instar of M. argentata and that of M. argyrocephala, the adult females of which are otherwise difficult to separate.