Laboratory assessment of resistance to commercial insecticide formulations in two strains of the German cockroach, Blattella germanica (L.) (Dictyo-ptera: Blattellidae)

Abstract The survivors of field treatments of Blattella germanica (L.) with ben-diocarb (strain D) and malathion (strain H) in the UK were bred in the laboratory. The resistance of these two strains to commercial formulations of bendiocarb, dioxacarb, propoxur, lindane, dieldrin, malathion, diazinon, fenitrothion, pirimiphos-methyl and permethrin was assessed in 24-h exposures on treated glass plates. Resistance in terms of knockdown or mortality was demonstrated for bendiocarb, dioxacarb and dieldrin in both strains, for malathion in strain H and, marginally, for permethrin in strain D. Selection with bendiocarb in strain D produced a x4 and x3 increase in resistance to bendiocarb at the LC50 and KD50 levels, respectively. There was no significant cross-resistance to propoxur, but cross-resistance to dioxacarb was evident at the LC50 and KD50 but not the 95 % levels. There was little or no cross-resistance in strain D to diazinon, pirimiphos-methyl or fenitrothion. In strain H, malathion selection increased resistance to malathion at the 50% but not the 95% levels, and there was no evidence of cross-resistance to diazinon, pirimiphos-methyl or fenitrothion. Some cockroaches from strains D and H were able to recover from knockdown during and after exposure to the carbamates and permethrin. There was no recovery from the organophosphorus or organochlorine insecticides.