permethrin toxicity and synergistic effect of pipernoyl butoxide in the first nymphal stage of blatella germanica (orthoptera: blattellidae)

trasal-contact method test using glass petri-dish rather than the conventional glass jar was used to evaluate the permethrin toxicity and synergism effect of piperonal butoxode (pbo) on nymphae of five strains of blattella germanica (l.). the test was carried out on 2-3 days old of first nympal stage, at four replicates of 10 cockroaches. the susceptible strain showed t50 and kt50 of 12.81 and 8.41 min, respectively. the order of resistance for all strains were gir>boy1>boy2>fay>sus. the wild strains showed resistance ratios varied over a range from 4.2 to 6.45 folds for mortality tests and 17 to 23.24 folds for knock-down tests. both methods of tests showed similar pattern of susceptibility in the wild strains. comparison of the resistance ratios for mortality and knock-down tests revealed that knock-down test has always showing higher resistance ratio than the mortality test. toxicity of permethrin alone or with the synergist at different ratios on the susceptible and resistant strains showed that the pbo has modified the response of the wild and susceptible strains to permethrin. the result indicated that increasing the amounts of synergist form 1 to 3 ratios in presence of insecticide effectively will increase the mortalities, compared with permethrin alone. the 1:3 ratio completely eliminates the resistance in the wild strains, indicating that pbo could inhibit the activity of mixed-function oxidases as a major metabolic pathway in the resistant strains.