ESTERASE-ACTIVITY AND ALLELE FREQUENCY IN-FIELD POPULATIONS OF SIMULIUM-EQUINUM (L) (DIPTERA, SIMULIIDAE) EXPOSED TO ORGANOPHOSPHATE POLLUTION

Esterase activity and allele frequencies in field populations of black fly larvae, Simulium equinum, were used in a preliminary study to iden tify any long-term genetic effects of low-level organophosphate insect icide exposure in rivers and streams. Esterase mean activity in S. equ inum collected downstream from a cress farm where malathion 60 was per iodically applied was significantly higher than in a population taken from a clean site. Polyacrylamide gel electrophoresis analysis of este rase electromorphs revealed that elevated esterase activity was correl ated with fast-running dark-staining alleles, whose frequency and acti vity was significantly higher in blackflies from the polluted site. Th e genetic differences at the cress sire may suggest a long-term exposu re to malathion selecting individuals with more active detoxification enzymes. A third S. equinum population was collected downstream from a trout farm and areas of substantial agricultural usage. Esterase acti vity and high activity allele frequencies were also significantly high er in this population. These preliminary results allow us to conclude that esterases in S. equinum have potential as long-term biomarkers of organophosphate pollution.