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

Abstract

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 through- out 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 activ- ity of larvae and the number of curves in the converging gallery increased. We inter- preted this observation as an avoidance behaviour of larvae to prevent intraspecific en- counters which could result in aggressive conflicts between two larvae.