Culex Pipiens In Shanxi Province Comparison Of Three Pyrethroid Selection Of Drug Resistant Strains And Their Viability

Obiective and method:In the laboratory the selection of resistant strain of Culex Pipiens Pallens of the Shanxi province to three kinds of Pytrthroid which was lambda-cyhalothrin,deltamethrin and tetramethrin was carried out using larve immersion method which was recommended by WHO.And the living capacity between the sensitive and resistant strains were compared.And the cross-resistance to other insecticides of the resistant strain of Culex Pipiens Pallens to lambda-cyhalothrin was studied.The results are listed in the following:Result:1,The selection of the resistant strainThe selection of the Culex Pipiens Pallens to deltamethrin was administered by the dose of LC₅₀ and LC₉₅,and the LC₅₀ of the selected strain increased 51 folds and 30 folds in LC₅₀ dose group and LC₉₅ dose group after 5 generations.The selection to lambda-cyhalothrin and tetramethrin both was carried out by the dose of LC₅₀,and increased 41.8 folds in lambda-cyhalothrin after 6 generations and the LC₅₀ of selected strains increased 13.07 folds after 3 generations of selection..2,Comparison of the living capacitySome biological parameters were compared between sensitive strain and resistant strain,it was found that the rates of blood-feeding and surviving in larvage and pupae of the resistant strain declined.Relative fitness of lambda-cyhalothrin deltamethrin and tetramethrin -resistant by net reproductive rates(R₀) were 0.41,0.47,0.29.3,Cross resistance The lambda-cyhalothrin-resistant strain showed high cross-resistance to some pyrethroids,including permethrin(41 folds),deltamethrin(22 folds) and cypermethrin(28 folds),but no cross-resistance were found to trichlofon,malathrion and propoxur.Conclusion:In the project it is found that the resistance to deltamethrin of the susceptible strain increased more quickly when it was selected with low dose than high dose;the selection of resistant strain of Culex Pipiens Pallens is easier in lambda-cyhalothrin and deltamethrin than in tetramethrin;and high cross resistance to pyrethriod of Culex Pipiens Pallens existed;and the living capacity of the resistant strains were low.These results give a clue that high dose but not low dose of insecticide should be suggested using.Discontinuous and rotational insecticide using could delay the resistant development to insecticides.