Scanning electron microscopy of the second-instar larva of Gasterophilus nasalis

The second-instar larva of the bot fly Gasterophilus nasalis (L.) (Diptera: Gasterophilidae) is described for the first time, based on scanning electron microscope (SEM) studies. On the pseudocephalum the larva bears an antenomaxillary sensory complex formed by the antenna (coeloconic sensilla) and the maxillary palp with a set of six coeloconic sensilla and four basiconica sensilla. The oral opening is latero-posteriorly limited by small spines, and exhibits strongly ornamented maxillae and mandibles. The thoracic and abdominal segments are circled by two bands, each with two rows (except the last segment that has one row) of backwardly pointed spines, and have cuticular depressions. Trichoid and campaniform sensilla surround the larval segments. The anterior spiracular opening is a small aperture. The terminal end of the eighth abdominal segment shows a spiracular cavity, lateral tubercles, eight basiconic and two trichoid sensilla. Each spiracular plate has two slightly curved slits, each with a serrated rima. There is a probable ecdysial scar. The findings of this ultrastructural study are compared with those other of larval flies.