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ISSN: 2161-1041
Hereditary Genetics: Current Research
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Pirimiphos-Methyl Resistance Status of Field Populations of Culex pipiens (Diptera: Culicidae) From Grand Tunis Area, Northeast Tunisia

Ahmed Tabbabi1*, Jaber Daaboub1,2, Ali Laamari1, Raja Ben Cheikh1 and Hassen Ben Cheikh1

1Laboratory of Genetics, Faculty of Medicine of Monastir, Monastir University, 5019, Monastir, Tunisia

2Department of Hygiene and Environmental Protection, Ministry of Public Health, 1006, Bab Saadoun, Tunis, Tunisia

*Corresponding Author:
Tabbabi A
Laboratory of Genetics, Faculty of Medicine
of Monastir, Monastir University, 5019
Monastir, Tunisia
Tel: 73500276
Fax: 73500278
E-mail: tabbabiahmed@gmail.com

Received date: April 17, 2017; Accepted date: April 28, 2017; Published date: May 05, 2017

Citation: Tabbabi A, Daaboub J, Laamari A, Cheikh RB, Cheikh HB (2017) Pirimiphos-Methyl Resistance Status of Field Populations of Culex pipiens (Diptera: Culicidae) From Grand Tunis Area, Northeast Tunisia. Hereditary Genet 6:175. doi:10.4172/2161-1041.1000175

Copyright: © 2017 Tabbabi A, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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Abstract

Mosquito species are responsible for the transmission of many parasitic diseases and their control leads to the phenomenon of resistance to insecticides. Five Culex pipiens samples were collected from various localities of Grand Tunis area, Northeast Tunisia, between June 2003 and November 2005. All the studied samples were resistant to pirimiphos methyl (organophosphorus insecticide). Our results showed the implication of insensitive acetylcholinesterase and overproduced esterases in the résistance of the Tunisian populations of Culex pipiens. Results were discussed in relation to resistance mechanism.

Keywords

Culex pipiens; Resistance; Pirimiphos-methyl; Insensitive acetylcholinesterase; Overproduced esterases; Northeast Tunisia

Introduction

In addition to their nuisance, mosquitoes cause vector-borne diseases [1-3] and their impact on human health is very considerable [4]. Worldwide, mosquito species such as Culex are responsible for the transmission of parasitic diseases such as filariasis, yellow fever and West Nile virus [5,6]. Mosquito control by insecticides is very effective on culicidae mosquitoes, but has several disadvantages. In addition to a detrimental effect on aquatic life, they can be the cause of various environmental problems [5], in particular the phenomenon of insect resistance to insecticides [7-12].

Due to the problem of resistance of vectors to chemical insecticides, several alternative insecticides have been developed to evaluate their efficiencies. Pirimiphos-methyl is an organophosphorus (OP) insecticide having a fast action with less toxicity for humans and environment. The use of this insecticide against mosquito adults has already been reported [13-15]. The low remanence of pyrimiphosmethyl, used as adulticide, is due to its high vapor pressure which diffuses it rapidly into the ambient atmosphere [16,17]. It should be mentioned that according to our knowledge, no published studies have been done on resistance of Culex pipiens to pirimiphos methyl in Tunisia.

The aim of this study was to determine the pirimiphos-methyl resistance status of field populations of Culex pipiens (Diptera: Culicidae) from Grand Tunis Area, Northeast Tunisia.

Materials and Methods

Study area

Grand Tunis is the name for the greatest metropolitan area in Tunisia, which assembles four of the following states: Tunis, Ariana, Manouba and Ben Arous.

Mosquitoes

Five Culex pipiens samples were collected at preimaginal stages from breeding sites in 5 localities between June 2003 and November 2005 (Table 1 and Figure 1). Reference strains included S-Lab, an insecticide-susceptible strain without any known resistance genes [18]. SA2 and SA5 were used as references of resistant strains with A2B2 and A5B5, respectively.

hereditary-genetics-Geographic-origin-Tunisian-populations

Figure 1: Geographic origin of Tunisian populations.

Code Locality Breeding sites Date of collection Mosquito control (used insecticides) Agricultural pest control
1 Sidi Thabet Ditch Aug, 2004 Rare (C, P) Yes
2 Sokra Canal June, 2003 Very frequent (C, Pm, F, P, D) Yes
3 Mannouba River June, 2005 Occasional (P, D) Yes
4 Ouardia Ditch Aug, 2005 Very frequent(C, F, P, D) None
5 Ezzahra Ditch Nov, 2005 Very frequent (C, F, P, D, T) None

Table 1: Geographic origin of Tunisian populations, breeding site characteristics and insecticide control.

Bioassays

Assays were performed as described by Raymond et al. [19], using ethanol solutions of pirimiphos methyl (99% [AI]), brought from laboratory Dr Ehrenstorfer, Germany, and propoxur (99.9% [AI], Bayer AG, Leverkusen, Germany). The effect on OPs resistance of 2 synergists, the DEF (98% [AI], Chem Service, England), and the Pb (94% [AI], Laboratory Dr Ehrenstorfer, Germany), was studied.

Over-produced esterases

Esterases were characterized on homogenates of adult thorax and abdomen according to the method of Pasteur et al. [20,21].

Data analysis

Data were subjected to probit analysis [22] using a BASIC program [19].

Results and Discussion

The linearity of the dose-mortality response was rejected for all samples, with the exception of S-Lab and 4 field samples (#2, 3, and 5). All the studied samples, collected between June 2003 and November 2005, were resistant to pirimiphos methyl. The RR50 ranged from 12.6 in sample #3 to 231 in sample #5 (Table 2). This can be explained by the massive use of this insecticide in the control against these insects but the survey carried out is not in agreement with the results found: only one locality by five prospected was the object of control by pirimiphosmethyl.

  Population Pirimiphosmethyl Pirimiphosmethyl +DEF Pirimiphosmethyl +Pb
LC50 in μg/l
(a)
Slope
± SE
RR50
(a)
LC50 in μg/l
(a)
Slope
± SE
RR50
(a)
SR50
(a)
RSR LC50in μg/l
(a)
Slope
± SE
RR50
(a)
SR50
(a)
RSR
Slab 2.9
(2.5-3.4)
2.34 ± 0.18 - 0.30
(0.16-0.56)
1.7 ± 0.42 - 9.79
(6.16-15.5)
- 0.40
(0.31-0.55)
1.47 ± 0.18 - 7.2
(5.7-9.1)
-
1-Sidi Thabet 67
(29-155)
1.16 ± 0.25 23.2
(15.2-35.5)
24
(16-35)
2.15 ± 0.32 82.2
(49.5-136)
2.77
(1.72-4.45)
0.28 43
(37-49)
2.34 ± 0.21 107
(85.5-133)
1.5
(1.04-2.3)
0.22
2-Sokra 135
(102-184)
1.17 ± 0.12 46.2
(37.4-57.1)
60
(32-110)
5.37** ± 3.46 201
(59.1-688)
2.24
(0.63-7.96)
0.22 37
(19-72)
2.52 ± 0.64 94.1
(61.2-144)
3.5
(2.1-5.7)
0.49
3-Mannouba 37
(31-43)
1.57 ± 0.13 12.6
(10.4-15.3)
6.9
(4.7-10)
1.21* ± 0.16 16.7
(12.1-23.0)
5.33
(4.22-6.72)
0.75 32
(15-66)
2.2 ± 0.7 80.3
(43.1-149)
1.1
(0.62-2.0)
0.16
4-Ouardia 38
(27-52)
2.52 ± 0.43 13.1
(9.02-19.0)
1.3
(0.33-2.9)
0.34 ± 0.08 4.5
(2.8-7.0)
28.5
(20.0-40.6)
2.9 23
(15-41)
1.07* ± 0.15 58.5
(44.4-77.2)
1.6
(1.09-2.4)
0.22
5-Ezzahra 676
(656-689)
19.2 ± 2.36 231
(172-311)
376
(258-789)
1.33* ± 0.32 1262
(726-2195)
1.79
(1.24-2.59)
0.18 27
(18-38)
2.8 ± 0.71 67.6
(44.2-103)
24.8
(15.6-39.3)
3.4

Table 2: Pirimiphosmethyl resistance characteristics of Tunisian Culex pipiens in presence and absence of synergists DEF and Pb.

The DEF decreased significantly the tolerance to pirimiphos methyl in S-Lab and the five field samples (SR50>1, p<0.05) (Table 2). The DEF had a synergistic effect significantly higher than that recorded in S-Lab (RSR>1) only in samples #4. Therefore, the increased detoxification by EST (and/or GST) was involved in the pirimiphos methyl resistance only in this sample. This mechanism accounts for only a part of this resistance because the RR50 remained significant in the presence of the DEF (RR50>1, p<0.05). The addition of Pb decreased significantly the tolerance to pirimiphos-methyl in S-Lab (SR50=7.24, p<0.05) and in samples #2 and #5, but the SR was significantly higher than that recorded in S-Lab only in sample #5 (Table 2). Therefore, the increased detoxification by the CYP450 was involved in the pirimiphos methyl resistance only in this population. This mechanism explains only a part of this resistance because RR50 remained significant in the presence of Pb (RR50>1, p<0.05). Our synergist study showed that the increased detoxification by EST (and/or GST) and CYP450 had only a minor role in the pirimiphos methyl resistance, results already confirmed by previous studies [23,24]. It should be noted that esterases, GSTs and cytochrome P450 enzymes are not always sensitive to used synergists.

Mortality caused by propoxur were 0% in sample #5 which showed the highest resistance levels to studied pirimiphos-methyl insecticide, 18% in sample #4, 21% in sample #2, 46% in sample #1 and 48% in sample #3. The mortality due to propoxur was significantly correlated with the LC50 of pirimiphos methyl (P<0.05) indicates an acetylcholinesterase insensitive. Five esterases were observed in 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 (and/or A5-B5, which has the same electrophoretic mobility) and B12. One or several esterases were detected in all the studied samples. The A1 esterases were observed only in samples #3 and #5, with a low phenotypic frequency of 0.03. The C1 esterases were observed only in samples #1 and #5, with a low phenotypic frequency of 0.06 and 011, respectively. The other esetrases were detected almost in all collected samples with frequency which vaired between 0.03 and 0.48. Esterases play an important role in the resistance of several insects in the world [25-31]. Our results confirms the previous results of Ben Cheikh et al. [28] which reported the existence of a correlation between the frequency of individuals possessing the Ace-1R allele and those overproduced esterases A and B among the Tunisian populations of Culex pipiens. However, other studies are not in agreement with these results and suggested that overproduction of esterases and modifications of AChE are not correlated [11,12].

Acknowledgements

This work was kindly supported by the Ministry of Higher Education and Scientific Research of Tunisia by funds allocated to the Research Unit (Génétique 02/UR/08-03) and by DHMPE of the Minister of Public Health of Tunisia. We are very grateful to S. Ouanes, for technical assistance, A. Ben Haj Ayed and I. Mkada for help in bioassays, S. Saïdi, Tunisian hygienist technicians for help in mosquito collecting, and M. Nedhif and M. Rebhi for their kind interest and help.

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