MORPHOLOGICAL DEFORMITIES IN CHIRONOMUS, CRYPTOCHIRONOMUS, AND PROCLADIUS LARVAE (DIPTERA, CHIRONOMIDAE) FROM 2 DIFFERENTIALLY STRESSED SITES IN TOBIN LAKE, SASKATCHEWAN

Morphological deformities in Chironomus plumosus type larvae from two differentially stressed sites in the Tobin Lake reservoir are described and compared. The frequency of deformities was 41.3% at Site 2 where larvae are directly exposed to contaminants entering the reservoir from the Saskatchewan River. At Site 17, where larvae are only indirectly exposed in a backwater area, the frequency was 31.8%. The frequency of deformities was higher at Site 2 in all head capsule structures except antennae. At Site 17, the significantly higher frequency of antennal deformities suggests that (1) antennae respond to contaminants according to a quantal dose-response relationship, (2) antennae and other head capsule structures may respond through different mechanisms or at different rates, or (3) other environmental factors may modify larval responses to contaminants. Descriptions of the deformities in other head capsule structures provide a framework for individual indices of severity of deformation similar to that developed previously for antennae. These eventually will be incorporated into an Index of Total morphological Respons. Deformities in Procladius and Cryptochironomus larvae are also described.