POSSIBLE MECHANISMS OF ORGANOPHOSPHORUS AND CARBAMATE INSECTICIDE RESISTANCE IN GERMAN COCKROACHES (DICTYOPTERA, BLATTELIDAE) FROM DIFFERENT GEOGRAPHICAL AREAS

The resistance status of 14 strains of Blattella germanica (L.) from four countries was determined for chlorpyrifos and propoxur compared with a standard reference susceptible strain. Thirteen strains were resistant to chlorpyrifos; 12 strains were resistant to propoxur. Resistance ratios for chlorpyrifos ranged from 8- to 462-fold at LC90; for propoxur, resistance ratios ranged from 4- to 46-fold. One cockroach strain from Denmark had negative cross-resistance to chlorpyrifos, and one strain from the United States had negative cross-resistance to propoxur. Slopes of probit regressions indicated that all resistant strains were heterogeneous for resistance to both chlorpyrifos and propoxur. Synergist studies with piperonyl butoxide indicated that multifunction mono-oxidases are probably involved in resistance to chlorpyrifos in six strains and in resistance to propoxur in seven strains. Esterase activity was elevated in 10 strains; of these strains, two had only slightly elevated esterase activity as measured with the substrates 1- and 2-naphthyl acetate. The remainder had higher levels of elevated esterase activity to both substrates. Strains with elevated esterase activity were resistant to a broad spectrum of organophosphates, pyrethroids, or both. Increased levels of glutathione S-transferase activity were found in four strains. Another two strains had a low frequency (1%) of individuals with high glutathione S-transferase activity. Elevated glutathione S-transferase activity was not correlated with the observed levels of organophosphate or carbamate resistance. One strain from Dubai had an altered acetylcholinesterase-based mechanism that conferred broad-spectrum resistance to a range of organophosphates and carbamates.