ABSTRACT
Abstract:tbackground:Chemicals are used for rapid control of large area; although misuse of those insecticide leads to resistance; resurgence of pests and finally replacement of insecticide which is unaffordable in developing Country.Objectives:This study aimed to determine the susceptibility status of Culex quinquefasciatus larvae to four organophosphate insecticides; Temephos; Fenthion; Fenitrothion and Chlorpyrifos.Material et methods.Following WHO standard protocols; larval susceptibility tests were carried out in 3 localities;namely Khartoum; Omdurman and Khartoum North. Mortality rates and lethal concentration (LC 50 and LC 95) were calculated for four types of organophosphate insecticides: includes; Temephos; Fenthion; Fenitrithion and Chlorpyrifos.results: Susceptibility of Culex quinquefasciatus; prevalent in the three greater localities of Khartoum State was determined against four organophosphates (Temephos; Fenitrothion; Fenthion and Chlorpyrifos) were confirmed resistant (mortality below 80). Studies were carried out on late 3rd or early 4th instar larvae of these species using standard WHO technique. Based on concentration mortality data LC 50 and LC 95 values were calculated. LC 50 values as observed for the above four insecticides in the three greater localities Khartoum North ; Khartoum and Omdurman for Fenitrothion were 0.8097; 0.0398 and 0.0432?g per litre ; for Temephos 0.47; 3.85 and 12.82 ?g per litre and for Fenthion .15; 0.11 and 0.91 ?g per litreand finally for Chlorpyrifos 0.31; 0.39 and 13.76 ?g per litre respectively.Conclusion: The study concluded that;Cx. quinquefasciatus larvae in Khartoum State create a resistance to the tested larvicides(Fenthion;Temephos; Fenitrothion and Chlorpyrifos).recommendations:Use of non-chemical control methods in addition to using insecticide mixture is important tactics to manage insecticides resistance