Monitoring insecticide resistance in house flies (Diptera : Muscidae) fromNew York dairies

House flies were collected from dairies across New York state and the level s of resistance to seven insecticides were measured using standard laborato ry assays with three to five diagnostic concentrations. The highest levels of resistance were found for tetrachlorvinphos, permethrin and cyfluthrin. Although levels of resistance to methomyl were somewhat lower, they were am ong the highest ever reported for held-collected house flies. Resistance to pyrethrins was limited primarily to the lowest diagnostic concentration. H ouse flies were susceptible to fipronil at all dairies, suggesting that thi s material would be highly effective for fly control. The levels of resista nce were similar at ah the dairies, irrespective of their insecticide use, suggesting substantial movement of flies between facilities. Relative to re sistance levels found at New York dairies in 1987, resistance levels had in creased for permethrin, were unchanged for tetrachlorvinphos and had. decre ased for dimethoate. To identify a single diagnostic concentration that cou ld be used in the laboratory assays to assess accurately resistance levels in future studies, we carried out a 'simulated' field bioassay using formul ated materials. A diagnostic concentration for each insecticide is proposed on the basis of a comparison of our bioassays. (C) 2001 Society of Chemica l Industry.