Ecological aspects of the external morphology and functionality of the psychomyiid female ovipositor (Insecta,Trichoptera)

Females of most psychomyiid species bear an elongated ovipositor enabling them to oviposit their eggs into grooves and cavities in different kinds of substrates in freshwaters. Although the preference of psychomyiid species for oviposition into distinct substrates and the subsequent larval life performance in aquatic habitats is already known, the mode of oviposition and the functional morphology of the elongated ovipositor have not been described until now. In this study we present SEM photographs of some psychomyiid species with female ovipositors of different lengths and shapes, explaining their preference for oviposition into distinct substrates. Additionally, we discuss some ecological aspects of the ovipositor shapes and the mode of egg laying for psychomyiids. The female ovipositor consists of two body segments, with an elongated IXth and a distinctly shorter Xth segment, which is flexible and can be pushed up dorsally when releasing the eggs. On the basis of SEM photographs, we suppose that the opening of the channel through which the eggs were released is located ventrally near the ovipositor tip. The ovipositor itself is characterised by a ventral cleft reaching from the gonoporus of segment IX to the tip of the last segment X. We stored adult females abdomina overnight in different aqueous dilutions of ethanol leading to different stages of swelling of the ovipositors (grade of swelling in distilled water >30% ethanol >70% ethanol). Some internal membrane-like structures, normally infolded into the ovipositor, became visible by the swelling of the ovipositor. We discuss the possible rearrangement of the organisation of segment IX resulting in the development of an ovipositor on the basis of SEM photographs of the differently swollen ovipositors.