Esterase activity and allele frequency in field populations of Simulium equinum (L.) (Diptera: Simuliidae) exposed to organophosphate pollution

Abstract

AbstractEsterase activity and allele frequencies in field populations of blackfly larvae, Simulium equinum, were used in a preliminary study to identify any long‐term genetic effects of low‐level organophosphate insecticide exposure in rivers and streams. Esterase mean activity in S. equinum collected downstream from a cress farm where malathion 60 was periodically applied was significantly higher than in a population taken from a clean site. Polyacrylamide gel electrophoresis analysis of esterase electromorphs revealed that elevated esterase activity was correlated with fast‐running dark‐staining alleles, whose frequency and activity was significantly higher in blackflies from the polluted site. The genetic differences at the cress site may suggest a long‐term exposure 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 activity and high activity allele frequencies were also significantly higher in this population. These preliminary results allow us to conclude that esterases in S. equinum have potential as long‐term biomarkers of organophosphate pollution.