Evaluation of resistance to temephos insecticide in Culex pipiens pipiens larvae collected from three districts of Tunisia.

BACKGROUND: Mosquitoes are considered as the main groups of arthropods that cause nuisance and public health problems. OBJECTIVES: Evaluation of resistance to temephos insecticide in Culex pipiens pipiens larvae collected from three districts of Tunisia. METHODS: Late third and early fourth instars larvae of Culex pipiens pipiens were collected in three localities of Northern and Southern Tunisia. Field collected populations were tested against temephos insecticide and compared to bioassays of a susceptible reference strain. The cross-resistance between temephos and propoxur, and the polymorphism of over-produced esterases and AChE 1 were investigated. RESULTS: Studied populations exhibited tolerance to temephos with low and high levels of resistance. The resistance ratio (RR50) values of temephos ranged from 1.34 to 114. Synergists and starch electrophoresis showed that the metabolic resistances were involved in the recorded resistance. Likewise, the resistant target site (acetyl cholinesterase: AChE 1) was responsible for the recorded resistance to temephos compound in Culex pipiens pipiens. CONCLUSION: The low and high resistance recorded to temephos insecticides is particularly interesting, because it leaves a range of tools useable by vector control services. However, further studies are needed to determine its spread and anticipate vector control failure where these insecticides are used.

Resistance status to deltamethrin pyrethroid of Culex pipiens pipiens (Diptera: Culicidae) collected from three districts of Tunisia.

OBJECTIVES: The aim of the present study was to determine the susceptibility status of Culex pipiens pipiens populations against deltamehtrin insecticide. METHODS: Larvae of Culex pipiens pipiens were collected from three breeding places in Northern and Southern Tunisia between 2003 and 2005. Early third and late fourth instars were tested against deltamethrin pyrethroid insecticide. Cross-resistance with DDT resistance was evaluated in studied samples to estimate the role of target site insensitivity and two synergists including piperonyl butoxide (Pb) and S,S,S-tributyl phosphorotrithioate (DEF) were used to estimate the role of detoxification enzymes. RESULTS: Our results revealed that the level of deltamehtrin resistance ranged from 0.67 to 31.4. We also showed the non-involvement of kdr resistance in pyrethroid resistance and no cross-resistance with DDT resistance was detected in all studied populations including the most resistant one. Synergists study on the resistant population (sample # 1) showed the involvement of CYP450 in the recorded resistance to the deltamethrin insecticide. CONCLUSION: The results obtained from this study should be considered in the current control programs to combat mosquitoes in Tunisia.

Resistance development and insecticide susceptibility in Culex pipiens pipiens, an important vector of human diseases, against selection pressure of temephos and its relationship to cross-resistance towards organophosphates and pyrethroids insecticides.

BACKGROUND: Culex pipiens pipiens is an important vector of human diseases. OBJECTIVE: To determine the insecticide resistance development in Culex pipiens pipiens against selection pressure of temephos.. METHODS: A field population of Culex pipiens pipiens was collected from Northwestern Tunisia with a medium level of temephos resistance (LC50 = 0.0069). It was subjected to six generations of temephos pressure selection to evaluate its relationship to cross-resistance towards organophosphates (OPs) and pyrethroids (PYR) insecticides. RESULTS: The selection was initiated at the dose 0.0266, 0.0748 and 0.0069 which were increased during successive generations up to 0.1488, 3.8747 and 0.0086 after sixth generation for temephos, chlorpyrifos and permethrin insecticides, respectively. It is important to noted that high cross-resistance to chlorpyrifos insecticide (OP) was detected (51.88×). However, little or no cross-resistance to the pyrethroid permethrin (PYR) was recorded (1.24×). Contrary to metabolic resistance, it seemed that acetylcholinesterases AChE 1 was fixed under pressure selection. CONCLUSION: The high cross-resistance to temephos and chlorpyrifos is reasonable because they belong to the same class of insecticide (OP). However, the little cross-resistance to the pyrethroid permethrin could support its use alternately for Culex pipiens pipiens control.