Field Evaluation of Synergized Permethrin for Control of Permethrin-resistant House Flies! on Southern California Dairies

Field applications of permethrin wettable powder (WP) and permethrin WP plus piperao}'! butoxide (PB) (1:5) were evaluated for control of permethrin~resist.ant house flies on dairies at two different areas in Southern California. Multiple applications of pennethrin WP or permethrin WP plus PB bet\veen June and October 1986 did not influence significantly the levels of resistance to pennethrin, as detennined by laboratory bioassays on house nics collected just before (June) and soon after (November) the treatment period. The addition of PB to permethrin for the June and November bioassays of field populations strongly increased permethrin toxicity, indicating that a major portion of the resistance was due to mixed-function oxidases. However, the mixture of penncthrin plus PB did not provide significant improvement in control over that achieved by permethrin alone. The limitations of current PB formulations for usc with insecticides with long residual stability is discussed.