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

Avoidance behaviour in the gallery construction of Tinodes unicolor (Psychomyiidae, Trichoptera) to prevent intraspecific encounters

Larvae of the psychomyiid caddisfly Tinodes unicolor construct tunnel-like, fixed retreatments (galleries) on stone surfaces in small streams. Larvae were reared during a laboratory study in a streamwater-filled aquarium under controlled light and temperature conditions. The gallery construction behaviour of larvae was investigated at 8 dates within 6 months by plotting each gallery on the front pane of the aquarium on a transparent foil. Gallery length and the distances to the neighbouring galleries were measured and the number of curves in each gallery counted. On each surveying date this procedure was repeated one week later to investigate the short-term gallery construction behaviour of larvae. Gallery lengths remained relatively constant throughout the 6 month study period. The analysis of the short-term surveys displayed that the distance to the next gallery of a conspecific decreased with increasing length of the galleries. With decreasing distance to the neighbouring gallery the construction activity of larvae and the number of curves in the converging gallery increased. We interpreted this observation as an avoidance behaviour of larvae to prevent intraspecific en-counters which could result in aggressive conflicts between two larvae

Mouthparts, gut contents, and retreat-construction by the wood-dwelling larvae of Lype phaeopa (Trichoptera : Psychomyiidae)

The larvae of Lype phaeopa (Stephens, 1836) are found on dead wood substrates in streams and lakes. Gut content analyses, scanning electron microscopy of larval mouthparts, and gallery structure revealed characteristics of this habitat preference. The guts of the larvae contained mainly wood fragments whereas other food items (detritus, algae, fungi, inorganic particles) were much rarer. The suitability of the mouthparts to scrape wood surfaces, and the adaptative elongation of the silk-secreting spinneret, which facilitates the construction of retreats consisting of a tunnel-like silken net incorporating mainly wood fragments, are discussed. Retreat-construction under laboratory conditions indicated that larvae exploit new feeding areas by steadily extending their galleries. Tips of the maxillary palps bear five sensilla styloconica and five sensilla basiconica, almost all bearing an apical pore. Three sensilla styloconica, two with an apical peg, and two small inconspicious sensilla basiconica are located on the galea. Possible function of these sensilla is discussed on the basis of studies on the closely related sister-group of Lepidoptera