Genetics of resistance of pyrethroid-selected houseflies,Musca domestica L.

Four resistance factors were isolated genetically from the NPR strain of houseflies (Musca domestica L.), which resists natural pyrethrins, and were characterised toxicologically. The four factors were : pen, which reduces the rate of penetration of insecticides through the cuticle; kdr-NPR, a general pyrethroid resistance mechanism unaffected by the synergist sesamex; py-ses, a mechanism of resistance to natural pyrethrins that can be suppressed by sesamex; and py-ex, a factor that gives strong resistance to synergised natural pyrethrins and to the new synthetic esters, e.g. resmethrin, but little or none to natural pyrethrins alone.