The ecology of black flies (Diptera: Simuliidae) in some southern California streams.

Abstract

The ecology of black flies (Diptera: Simuliidae) in 2 distinct biotopes, desert and mountain streams, was studied in southern California, USA. The multivoltine species Simulium argus was the dominant species breeding in a warm, uniformly flowing limnocrene (a stream fed by a pond) during March 1978–July 1979. In this stream 4 other less abundant species, Simulium tescorum, S. aureum, S. vittatum and S. virgatum , were found associated with the larval and pupal populations of S. argus . The larval-pupal populations of S. argus had 2 peaks per year; however, they were most abundant in May–June. S. canadense (bivoltine) and S. piperi were found to be the dominant simuliids in the San Jacinto River (North Fork) and Indian Creek, respectively, during July–November 1978 and June–November 1979. Both of these streams are rheocrenes located in the San Jacinto Mountains and are fed by cool mountain springs and melting snow. Computer analysis revealed that the following abiotic (independent) variables, listed in descending order of importance, significantly affected the larval-pupal density (dependent variable). For S. argus these were day length, water temperature, air temperature, wind velocity and pH; for S. piperi they were water depth, water velocity, air temperature and precipitation; for S. canadense the only significant variable was water velocity. The interrelationships among the biotic and abiotic variables together with their biological impact on larval-pupal populations are discussed.