Chulalongkorn Medical Journal


Background: The German cockroach has been known as the most invading human dwelling cockroach species.For managing the insecticide resistance, it is periodically a substantial need to evaluate susceptibility level ofthe German cockroaches to consuming insecticides.Objective: To evaluate resistance of the German cockroaches to malathion, propoxur and lambdacyhalothrin.Methods: Three cockroach strains including susceptible reference, and two wild strains were provided,maintained and colonized. The wild strains were collected from two hospitals of Sanandaj in Iran. Surfacecontact method was used for bioassay using standard glass jar procedure. The adult male cockroaches weretreated with 5 - 6 insecticide dose exposures at a 30-min period. The dose exposures of malathion were 6.25, 12.5,25, 50 and 100, and 25, 50, 100, 200 and 400 mg/m2 for susceptible and wild cockroach strains, respectively.The dose exposures of propoxur were 5, 10, 20, 40 and 80, and 20, 40, 80, 160 and 320 mg/m2 for susceptible andwild cockroach strains, respectively. The dose exposures of lambdacyhalothrin were 0.075, 0.15, 0.3, 0.6 and 1.2,and 0.3, 0.6, 1.2, 2.4 and 4.8 mg/m2 for susceptible and wild cockroach strains, respectively. Each dose exposureswere replicated 3 times (10 cockroaches for each replicate). Control groups received acetone alone.Results: The lethal doses50 (LDs50) of the susceptible strain were 30.01, 16.56 and 0.303 for malathion, propoxurand lambdacyhalothrin respectively. While the LDs50 of the wild cockroach strains were 157.45, 74.59 and 0.506for malathion, propoxur and lambdacyhalothrin, respectively. Compared to the susceptible strain, the wildGerman cockroach strains were more tolerant to malathion and propoxur. Compared to the susceptible strainthe wild German cockroach strains were more sensitive to lambdacyhalothrin, confirmed also by a significantdifference (P = 0.033). The results of probit analysis and regression lines of treated insecticides indicate thatthe German cockroach was resistant to malathion and propoxur while susceptible to lambdacyhalothrin.The resistance ratio50 (RR50) of the malathion and propoxur insecticides were about 5.0 folds.Conclusion: The study supports that malathion and propoxur should not be used for control of the Germancockroaches. An appropriate choice is to use lambdacyhalothrin due to negative cross-resistance effect whichoccurs here. The study also provides a baseline of resistance data towards a few insecticides in a few Germancockroach populations in Iran.


Faculty of Medicine, Chulalongkorn University

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