Distribution dynamics of epilithic insects in a lake littoral

Abstract

The freshwater epilithic insect community in the littoral of Crose Mere, a eutrophic lake in the English Midlands, was investigated monthly from February 1993-February 1994. Larvae were collected from patches of stones either shaded by bankside trees or well away from trees and from either shallow water at the edge or from deeper water. The invertebrate community was dominated by gallery-building larvae of the psychomyiid caddis, Tinodes waeneri, and four species of chironomids with tube-dwelling larvae, Cricotopus sylvestris, Microtendipes pedellus, Glyptotendipes pallens and Endochironomus albipennis. The early instars of Tinodes, Cricotopus and Microtendipes showed peaks of density in shaded habitats in spring and summer, suggesting that adults had oviposited beneath trees. Adult Tinodes and chironomids were also found to be associated with trees and other vegetation along the shore, avoiding areas of closely-grazed grass. The subsequent distribution of later larval instars demonstrated that larvae had dispersed to open and deep habitats. Despite the apparently more favourable conditions for gazers in unshaded habitats, adult Tinodes, Cricotopus and Microtendipes did not oviposit in the open. Oviposition behaviour may have evolved in these species that minimises the risk to the gravid female, rather than maximises the survival of larvae.