Spatio-temporal distribution of size classes and larval instars of aquatic insects (Ephemeroptera, Trichoptera and Lepidoptera) in a Potamogeton pectinatus L. bed (Lake Geneva, Switzerland)

Abstract

Spatio-temporal distribution of size classes and larval instars of aquatic insects in a Potamogeton pectinatus L. bed (Lake Geneva, Switzerland). -Temporal changes of aquatic insect instars or size classes were monitored in different parts of a Potamogeton pectinatus bed. The hypothesis of a different distribution of the aquatic insects in the macrophyte bed according to their life stage and of a spatio-temporal segregation of congeneric species was tested. Head capsules widths of seven insect species (Caenis horaria and C. luctuosa (Ephemeroptera), Mystacides azurea, M. longicornis, Oecetis lacustris and O. ochracea (Trichoptera) and Acentria ephemerella (Lepidoptera)) were measured at monthly intervals from May to November 1994. Samples were taken in the edge and in the centre of the macrophyte bed on all sampling occasions, and in May, June and July, additional samples were taken from the 2 m sediment belt adjacent to the macrophyte bed. Each couple of congeneric species showed segregation by size before hibernation and showed delayed emergence patterns.