Effects of Synergists on Bendiocarb and Pyrethrins Resistance in the German Cockroach (Dictyoptera: Blattellidae)

Several field-collected strains of German cockroaches, Blattella germanica (L.), were tested for resistance to bendiocarb or pyrethrins or both in the presence or absence of synergists. Large nymphs were exposed to toxicants on glass surfaces. All strains tested had high-level resistance to bendiocarb: a few were highly resistant to pyrethrins. The synergists piperonyl butoxide and MGK 264, 2-(2-ethylhexyl)-3a,4,7,7a-tetrahydro-4,7-methano-1H-isoindole-1,3(2H)-dione, both successfully negated resistance to bendiocarb and pyrethrins. Combinations of these insecticides with either synergist also effectively eliminated resistance. A commercial product (Ficam Plus) containing bendiocarb, pyrethrins, and piperonyl butoxide rendered eight bendiocarb-resistant strains susceptible. These results indicate that the resistance mechanism to both bendiocarb and pyrethrins probably may be attributed to an enhanced microsomal mixed-function oxidase system which is effectively inhibited by either synergist.