Comparative modification of insecticide‐resistance spectrum of Culex pipiens fatigans wied. By selection with temephos and temephos/synergist combinations

The evolution of strong organophosphorus multiresistance, suppressible by S,S,S‐tributyl phosphorotrithioate (TBPT), in a California strain of Culex pipiens fatigans was examined by further selection with temephos, alone and in combination with the synergists TBPT or piperonyl butoxide (PB). Selection by temephos and temephos + PB increased resistance to higher levels. However, selection by temephos + TBPT virtually abolished TBPT‐suppressible resistance while preventing the emergence of significant alternative resistance mechanisms. The phenomenon of synergism may enable the extended use of an insecticide where alternative resistance mechanisms are either absent or of low efficiency in the target population.