Responses of Immature Blackflies (Diptera: Simuliidae) to Experimental Pulses of Acidity

Abstract

An investigation to determine the responses of immature blackflies to experimental pulses of acidity simulating snowmelt episodes was conducted. Five species of mature blackfly larvae were subjected to 3- or 4-d experimental pH depressions to approximately 4.0 or 3.5 in stream channels. Differences among species in response to acidity were observed. All species except Simulium vittatum and possibly S. venustum were able to tolerate pH depressions to approximately 4.0, while only Cnephia dacotensis and possibly S. decorum were able to tolerate pH depressions to approximately 3.5. The survival of the larvae (only late instars were tested) was significantly affected by the acidity, while pupal survival generally was not. The rate of pupation, however, was decreased in the acidified channels, resulting in decreased emergence there also. More abnormally formed pupae developed in the acidified channels, suggesting that pupation following snowmelt ensures survival of these species.