Abstract
The effects of three synergists on the level of resistance to eight pyrethroids were examined in field-collected populations of the German cockroach, Blattella germanica (L.). Resistance to allethrin was not affected by piperonyl butoxide (PBO), (2-(2-ethylhexyl)-3a,4,7,7a-tetrahydro-4,7-methano-1H-isoindole-1,3(2H)- dione (MGK 264), or S,S,S-tributyl phosphorotrithioate (DEF). Resistance to pyrethrins also was not affected by these synergists in the same or similar strains but was negated almost completely by them in strains resistant only to pyrethrins. Resistance to permethrin, cypermethrin, and cyfluthrin largely was negated by these synergists. Results were variable with esfenvalerate, fenvalerate, and especially phenothrin. For example, with phenothrin the synergists were partially effective against some strains but were totally ineffective against others. The results appear to be unrelated to the chemistry of the pyrethroids studied. I report evidence that indicates the possible presence of several independent resistance mechanisms. My results suggest that these synergists generally will not combat pyrethroid resistance in this species, although they are highly effective in some cases.
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