Variation in general esterase activity within a population of Haematobia irritans (Diptera : Muscidae)

Control of the horn ny, Hematobia irritans (L.), is generally dependent on chemical insecticides. However, the biology and behavior of the horn ny fav ors rapid development of insecticide resistance. To prolong the effectivene ss of the insecticide option. information is required regarding the mechani sms of insecticide resistance. Metabolic hydrolysis of insecticides by este rases is a detoxification mechanism in many insect species. Measurement of general esterase activity within populations of horn flies may provide a di agnostic tool for resistance management. In this study. we evaluated the am ount of variation in general esterase activity within female and male horn fly samples from a population that had not been exposed to insecticides for 8 yr. We found considerable variation in general esterase activity within samples of each sex, with females demonstrating tile greater variation. The observed variation is thought to be the result of age-structure dynamics w ithin the population. The amount of inherent variation makes it difficult t o detect small mean differences between populations, thus limiting the util ity of general esterase assays. Thus, effective diagnosis of esterase-media ted resistance mechanisms can only be achieved by the identification of spe cific detoxification esterases and the design of assays, either biochemical or molecular, for their detection and measurement.