Prevalence of insecticide resistance in field-collected populations of the German cockroach, Blattella germanica (Linnaeus) (Dictyoptera : Blattellidae) in Peninsular Malaysia

Thirty one field-collected strains of German cockroaches, Blattella germanica (L.), collected between February 1997 and March 2000 from various locations in Peninsular Malaysia were screened for insecticide resistance using topical application method against three commonly used insecticides (propoxur, chlorpyrifos and deltamethrin). A discriminating dose (LD_99) obtained from bioassaying a laboratory susceptible strain, was used to determine the prevalence of insecticide-resistant individuals among the field populations tested. Results indicated that both propoxur and deltamethrin resistance patterns were relatively similar, i.e. more than 50% of the strains screened show low to moderate level of tolerance, while chlorpyrifos resistance is still relatively low among the tested populations. Resistant gene frequencies estimated ranged between 0.01 to 0.78, 0.05 to 0.51 and 0 to 0.86 for propoxur, chlorpyrifos and deltamethrin, respectively.