01640naa a2200313 a 450000100080000000500110000800800410001910000210006024500770008126000090015852008690016765000130103665000130104965000240106265000150108665000110110165000170111265300120112965300130114165300130115465300110116765300160117865300200119465300150121470000140122970000150124370000160125877300520127418055612017-03-30       2001    bl uuuu     u00u1 u    #d1 aBARROS, A. T. M.  aHorn fly (DipterabMuscidae) resistance to organophosphate insecticides.  c2001  aInsecticidal ear tags impregnated with organophosphate (OP) insecticides were used each year from 1989 to 1998 at Rosepine, LA. Weekly fly counts were conducted to evaluated control efficancy of the treatments, and bioassay were conducted at least twice per year to measure fly susceptibility to OP and pyrethroid insecticides. Between 1989 and 1992, the efficacy of 20% diazinon-impregnated ear tags was reduced from &gt20 to just 1 week of control. A high risk of control failure was observed when a resistance frequency of approximately 5% was measured in pre-season bioassays. Resistance to diazinon, fenthion, ethion, pirimiphos-methyl, and tetrachlorviphos was observed. Esterase activity toward -naphthyl acetate was significantly higher in flies collected at Rosepione in 1997 than in flies from a laboratory colony and from a susceptible field population.  aMuscidae  aDíptera  aHaematobia Irritans  aInseticida  aInseto  aResistência  aControl  aControle  aHorn fly  aInsect  aInsecticide  aMosca do chifre  aResistance1 aOTTEA, J.1 aSANSON, D.1 aFOIL, L. D.  tVeterinary Parasitologygv.96, p.243-256, 2001.