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Culex pipiens pipiens is an important vector responsible for West Nile virus outbreaks that have recently affected many areas of Tunisia, and the use of vector control insecticides is the most powerful and widely applied system for the control of the disease. Our purpose was to measure the impact of mosquito control on temephos resistance status of Culex pipiens pipiens. An evaluation of resistance to temephos in three field-collected populations of Culex pipiens pipiens between 2003 and 2005 was conducted in northern and southern Tunisia. The three collected populations showed low resistance ratio for temephos insecticide in all studied samples which ranged from 1.52-fold in sample #1 to 0.50-fold at the LC50 level in sample #2. The use of two synergists showed that the increased detoxification by the Cytochrome P450 (CYP450) was involved in the temephos resistance in sample #1. Biochemical assay demonstrated that detoxification esterases were involved in the recorded resistance although they were not detected using synergist bioassays. Altered AChE gene was detected in all field populations. The low resistance observed in Tunisian populations of Culex pipiens pipiens is particularly interesting because it leaves a range of tools useable by vector control services. [ABSTRACT FROM AUTHOR]

Tunisian populations of Culex pipiens pipiens, an important vector of human diseases, have developed resistance to organophosphate insecticides. To understand the origin of this resistance, knowledge of the impact on agricultural pest and mosquito control activities and its significance for the resistance mechanisms will be required. Five populations of C. p. pipiens were collected at various sites with different agricultural pest and mosquito control activities throughout Tunisia and tested for fenitrothion resistance level. Results were compared to those obtained from a control population where no chemical activities have been carried out. Our results strongly suggest the presence of a correlation between agrochemical products and the recorded resistance despite a rather limited number of studied sites (five populations). On the other hand, organophosphates control activities let us suggest the existence of an important impact on fenitrothion resistance. However, it appears that the application of pyrethroids have little to no impact on fenitrothion (organophosphate) resistance. The recorded resistance of the control population should be due to anthropogenic factors; however, the combined effect of migration and gene flow on the evolution of insecticide resistance should also be taken into consideration. The recorded resistance was mediated by both enzymatic detoxification and target-site sensitivity. Our findings showed a positive correlation between both metabolic and target site resistance and the level of resistance. In conclusions, we can say that the use of pesticides and insecticides by both agricultural and public health departments in Tunisia should be more rationalized to reduce the development of resistance in C. p. pipiens populations. [ABSTRACT FROM AUTHOR]

Abstract: In this study, we investigated resistance to the organophosphates chlorpyrifos in Tunisian populations of Culex pipiens pipiens. Three field populations were collected from Northern and central Tunisia between 2003 and 2005 and used for the bioassays tests. Our results registered moderate and high levels of resistance to chlorpyrifos which ranged from 33.8 to 111. The chlorpyrifos resistant populations were highly resistant to propoxur indicated an insensitive acetylcholinesterase 1 (AChE 1). The highest frequency of AChE 1 resistant phenotypes (64%) was recorded in the most resistant population (sample # 1). Bioassays conducted in the presence of synergists showed that not esterases were involved as the resistance mechanism to chlorpyrifos. However, CYP450 was partly involved in the resistance of the most resistant sample (# 1). Starch electrophoresis showed that three esterases were present in studied samples: A2‐B2, A4‐B4 and B12. Results are discussed in relation to the selection pressure caused by insecticide treatments. [ABSTRACT FROM AUTHOR]

Culex pipiens is considered the potential vector of West Nile virus outbreaks that have affected Tunisia. The objective of the present study was to evaluate the fenitrothion insecticide resistance status of Culex pipiens pipiens in three populations of insects from three Tunisian states. Standardized method bioassays were conducted to shed light on fenitrothion susceptibility status in field Culex pipiens pipiens populations.The cross-resistance between fenitrothion and propoxur, and the polymorphism of over-produced esterases and AChE 1 were also investigated. Resistances to fenitrothion were moderate and low in sample # 2 and 3 (12.9 and 7.2, respectively). The highest resistance ratio was observed in populations collected in Northern Tunisia (sample # 1) with a rate of 60.9 fold at the LC50 level. The use of a synergist suggested the non-involvement of CYP450, esterases and/or glutathione-S-transferase in resistance of Culex pipiens pipiens to the tested insecticide. However, the biochemical investigation of detoxification enzymes using starch electrophoresis showed the involvement of four esterases, including A2-B2, A4-B4 (and/or A5–B5), B12 and C1. The fenitrothion resistant populations were highly resistant to propoxur indicating the possible involvement of their common target site (AChE 1) in the recorded resistance. Our results are particularly interesting to update the information base for rational deployment of the existing tools for mosquito's control. [ABSTRACT FROM AUTHOR]

The present study was undertaken to analyze the resistance status of Culex pipiens pipiens (C. p. pipiens) to the chlorpyrifos insecticide in Tunisia. Three mosquito populations of C. p. pipiens were collected from three districts of Tunisia between 2003 and 2005. Results obtained here showed that all populations were resistant to used insecticide and the level of resistance varied widely between the samples. The resistance ratios at LC50 (RR50) to chlorpyrifos ranged from 8.75 to 455. A synergism study showed that resistance to chlorpyrifos was affected (SR50 > 1, p < 0.05) by piperonyl butoxide (Pb), indicating the involvement of P450 oxidases detoxication in the recorded resistance of sample #1. However, esterases and/or glutathione S-transferase (GST)-mediated detoxication were not involved. Bioassays showed that resistance to chlorpyrifos and propoxur was correlated, suggesting an insensitive acetylcholinesterase (AChE 1). The highest frequencies of the resistant phenotypes ([RS] and [RR]) (0.74) were detected in the most resistant sample (#1). Five esterases were detected in the studied field samples. The esterase C1 encoded by the Est–1 locus and four esterases encoded by the Ester super locus: A1, A2–B2, A4–B4 (or A5–B5, which has the same electrophoretic mobility) and B12. [ABSTRACT FROM AUTHOR]

Conventional insecticides are among the most popular chemical control agents against mosquitoes. Our study aimed to evaluate the resistance status to permethrin (pyrethroid insecticide) in Culex pipiens pipiens (Diptera: Culicidae) from Tunisia. For this study, three samples of C. p.pipiens mosquitoes were collected from Northern and Southern Tunisia between 2003 and 2005. Early third and late fourth instar larvae were morphologically identified and used for bioassays. All samples were resistant to permethrin and a large variation ininsecticide tolerance was observed between samples. The RR50 values ranged from 3.01 in El Fahs to 39.3 in Sidi Hcine. Resistance to pyrethroid and dichloro-diphenyl-trichloroethane (DDT) insecticides were negativelycorrelated, indicating a sensitive voltage-gated sodiumchannel (CNaVD) in the most resistant population. The use of synergits showed the involvement of CYP450 in the recorded resistance to permethrin in Sidi Hcine. Results were discussed in relation to previous studies and mosquito control. Data on resistance insecticide were provided to serve as a base for further resistance management interventions. [ABSTRACT FROM AUTHOR]