DISTRIBUTION DYNAMICS OF EPILITHIC INSECTS IN A LAKE LITTORAL

The freshwater epilithic insect community in the littoral of Crose Mer e, a eutrophic lake in the English Midlands, was investigated monthly from February 1993-February 1994. Larvae were collected from patches o f stones either shaded by bankside trees or well away from trees and f rom either shallow water at the edge or from deeper water. The inverte brate community was dominated by gallery-building larvae of the psycho myiid caddis, Tinodes waeneri, and four species of chironomids with tu be-dwelling larvae, Cricotopus sylvestris, Microtendipes pedellus, Gly ptotendipes pallens and Endochironomus albipennis. The early instars o f Tinodes, Cricotopus and Microtendipes showed peaks of density in sha ded habitats in spring and summer, suggesting that adults had oviposit ed beneath trees. Adult Tinodes and chironomids were also found to be associated with trees and other vegetation along the shore, avoiding a reas of closely-grazed grass. The subsequent distribution of later lar val instars demonstrated that larvae had dispersed to open and deep ha bitats. Despite the apparently more favourable conditions for gazers i n unshaded habitats, adult Tinodes, Cricotopus and Microtendipes did n ot oviposit in the open. Oviposition behaviour may have evolved in the se species that minimises the risk to the gravid female, rather than m aximises the survival of larvae.