Contribution to Larval Morphology of Horseflies (Diptera, Tabanidae) of the Hybomitra (s. str.) bimaculata Macq. Group from Northwestern Russia

Larval morphology is described for seven species of horseflies (Diptera, Tabanidae) of the Hybomitra (s. str.) bimaculata Macq. group: Hybomitra bimaculata (Macquart, 1826), H . ciureai (Séguy, 1937), H . distinguenda distinguenda (Verrall, 1909), H . lundbecki lundbecki (Lyneborg, 1959), H . lurida (Fallén, 1817), H . muehlfeldi (Brauer, 1880), and H. nitidifrons confiformis (Chvála et Moucha, 1971). Some differences from the previously published data are noted as concerns external morphology and the structure of the head capsule and mouthparts in the examined species. For example, a chaetoid field was found on the preanal and anal segments in H. lurida . The lateral grooves are absent and the dorsoventral grooves are poorly developed in Hybomitra n. confiformis . The details of mouthpart structure completely coincide with those described in the literature only for H. muehlfeldi , while the six remaining species reveal some differences. A detailed study of the submentum has shown that its structure can be used as an additional diagnostic character. The larvae of all the examined species clearly differ in the length ratio of the submentum notch and the submentum itself. The submentum of H. muehlfeldi larvae differs from that in other species in the degree of chitinization of the anterior end around the notch.