an electrophyiological investingation of target site insesitivity in permethrn-resistant and susceptible strain of anopheles stephensi

it was shown that permethrin resistance in adult anopheles stephensi is due to at least three separate mechanisms. cytochrome p-450s and esterases are responsible for two-thirds of the 8-fold enhanced tolerance of the dub-apr resistant strain as compared with a sensitive strain, ind-s. it was postulated that target site insensitivity is also involved. to test this hypothesis, we conducted a neurophysiological study with the thoracic nerves of adult female an.stephensi under perfusion with saline. spontaneous neural activity was recorded with saline alone and in the presence of permethrin. there was no change in the frequency of spontaneous firing dose of 10-3molar perethrin rapidly produced a 3-fold increase in firing rate in the susceptible strain. in contrast, the resistant strain did not respond to this concentration. in a cumulative dose assay, the susceptible strain responded to the lowest concentration of permethrin (10-3 molar), but the resistant strain required a much higher dose (10-8- 10+-7 molar) to produce the same rise in frequency of actin potentials. this strongly suggests that nerve insensitivity contributes to permethrin resistance in this mosquito.