Abstract
The purpose of this experiment was to detect the activity of some insecticides against strains of housefly resistant to azamethiphos and permethrin.The individuals of housefly were exposed to selective pressure under LD50 of used pesticides.The topical application was used for each pesticide at 1 microliter /female. Results indicated that there was no cross resistance for azamethiphos and permethrin with malathion ,cypermethrin , abamectin and thiamethoxam according to values of LD50's and resistance ratio for above insecticides. When a bioassay was tested on two resistance strains of housefly for azamethiphos and permethrin . However , results indicated that there was that across resistance to fenvalerate in stains resistant to azamethiphos and permethrin. Values of LD50 were 0.42 and 1.35 mu g/female and resistant ratio 60 and 192 fold for previous strains respectively. Also results indicated that synergist piperonyl butoxide (PB) reduced resistance ratio from 141.3 to 47fold in azamethiphos and from. 385 to 21.2 fold in permethrin. Results indicated that frequent use of pyrethroid insecticides caused high resistance ratio more than organophosphorous insecticides. According to the results it can recommened to use piperonyl butoxide to reduse resistance ratio.