RELEVANCE OF RESISTANCE RATIOS TO OPERATIONAL CONTROL IN THE GERMAN-COCKROACH (DICTYOPTERA, BLATTELLIDAE)

A simulated crack and crevice method of exposure to insecticides was d eveloped to ascertain the relationship between mortality produced by f ield-application rates and resistance ratios obtained by the time-mort ality method. Nymphal German cockroaches, Blattella germanica (L.), fr om strains of widely varying resistance backgrounds were tested with c hlorpyrifos, acephate, cyfluthrin, and cypermethrin. I observed an inv erse relationship between resistance ratios and 72-h crack and crevice mortality in all 4 cases. Gene frequency estimates paralleled resista nce ratios for cyfluthrin and cypermethrin. I concluded that time-mort ality resistance ratios provide a good indication of the level of resi stance in a given strain, and that resistance ratios > 3.0 signal pote ntial control failures in the field.