Micromorphology of egg and larva of Eristalis fratercula, with an updated key of Eristalis species with known third instar larvae (Diptera: Syrphidae)

Abstract: The flower- or hoverflies (Syrphidae) and particularly the subfamily Eristalinae, are known by their importance as pollinators in both natural and agro-ecosystems. Similar to other saprophagous eristalines, the larvae of Eristalis Latreille, 1804 are characterized by an elongated anal segment and a telescopic breathing tube. These features have given them the common name of rat-tailed maggots and allow them to develop in liquid or semi-liquid media loaded with decaying organic material. This paper presents the first description of the egg and the third-instar larva of the boreal species Eristalis fratercula (Zetterstedt, 1838). Morphological studies are presented based on cryo-scanning electron microscopy (cryo-SEM). After comparison with all other known species of the genus Eristalis with described preimaginal morphology, we conclude that main diagnostic character of E. fratercula is the presence of long branched spicules located in the upper margin on the lateral lips. Finally, we provide an updated key that includes the 15 Eristalis species whose third larval stages have already been described.

Key words: Diptera, Syrphidae, Eristalis, hoverflies, preimaginal morphology, egg, larva, cryo-SEM, Norway, Palaearctic Region