Pyrethroid resistance in flies : development of a resistance monitoring technique and studies on the mechanism of resistance in horn flies and house flies

Abstract

Biotic potentials were measured for susceptible and pyrethroid-resistant horn flies, Haematobia irritans (L.). Resistant horn flies were less fit than susceptible flies. Pyrethroid-resistance was a reproductive disadvantage under insecticide free conditions. This disadvantage may be integrated into a horn fly control program. A field technique was developed to monitor insecticide-resistance in horn flies. The technique quickly and successfully determined the amount of resistance present in various populations by using discriminating doses of insecticides. This technique is easier to use and simpler to prepare than current techniques. In vitro saxitoxin (STX) binding to proteins from the heads of susceptible and target-site insensitive house flies, Musca domestica L., and horn flies was measured. STX bound to a single type of high affinity site in house fly heads that had not been exposed to any insecticides. STX binding to horn fly heads was low and difficult to measure, but appeared to occur similarly to the mechanism in house flies. In vivo insecticide exposure rapidly (15 minutes) reduced STX binding to house fly heads and indicated that binding sites were associated with either two types of sodium channels, or two types of regulation, or both. Exposure to permethrin reduced binding to one type of site more than to the other. Exposure to cypermethrin or diazinon reduced binding to both sites equally. This work is the first report on the effects of in vivo insecticide exposure on STX binding to sodium channels in an insect. Susceptible and resistant house flies had similar amounts of sodium channel protein. In resistant flies, the ratio of the two types of binding sites differed from that of susceptible files. Only resistant flies showed behavioral and biochemical signs of recovery from intoxication by pyrethroids. Lipid extractions from heads of susceptible and target-site insensitive house flies indicated that both strains had similar amounts of lipids. Pyrethroid exposure, did not alter the turnover of lipids. Target-site insensitivity appears to result from an innate, regulatory response which reduces the number of functional sodium channels present after intoxication and is only effective against poisons that interact with sodium channels.