A comparative study of Chironomus riparius Meigen and Chironomus tentans Fabricius (Diptera: Chironomidae) in aquatic toxicity tests.

Chironomus riparius Meigen and Chironomus tentans Fabricius were examined under controlled conditions and exposed to the reference toxicants cadmium and lindane (gamma-hexachlorocyclohexane) to identify any differences that could have implications for their use in aquatic toxicity testing. Preliminary studies showed that both species could be cultured in the laboratory using similar methodology, resulting in the typical bimodal emergence of adult males prior to females. However, adults of C. riparius emerged earlier and in greater numbers than C. tentans. Comparative measurements of head capsule width and body length for the four larval instars revealed similar dimensions for each species up to and including the third instar. Fourth-instar larvae of C. tentans were considerably larger than those of C. riparius. Median lethal concentrations (LC50) determined over a 10-day exposure period suggested no difference in species response to cadmium; however, with increasing exposure time, C. tentans was significantly more sensitive to lindane. The investigations showed that the pattern of response was similar for the two species, and that both C. riparius and C. tentans are suitable test organisms for acute exposure assays.