CASE FEATURES OF CADDISFLY LARVAE (SERICOSTOMA-SELYSI) AS RELATED TO WATER VELOCITY AND POTENTIAL TO DRIFT

Variation in case characteristics of larvae of Sericostoma selysi (Pic tet 1865) as related to water velocity and resistance to passive entry into the drift was investigated in the field. Larvae from river secti ons of different current velocity (low: 0.30-0.35 m.s(-1) land high: 0 .60-0.65 m.s(-1)) were collected. Case and larval dry weight were weig hed; frontal and lateral surface areas of the cases were also measured . Larvae from highspeed waters had heavier and narrower cases than tho se from the low-speed waters. We believe that this is an adaptation in response to water velocity, which enables larvae living under conditi ons of high velocity to resist the drag forces of moving water.