| Abstract|| |
Background: Dengue hemorrhagic fever, vector by Ae. aegypti, is a world common public health problem, particularly in tropical and subtropical area including Thailand. Samut Songkhram also has an epidemic of this disease. To control the spread, we focus on decreasing Ae. aegypti larva in the area. In Samut Songkhram, people mostly use temephos, which might cause a resistance in mosquitoes. Aims: The purpose of this research is to test resistance of Ae. aegypti against temephos (GPO-1 and Zeolite) and compare temephos's resistant rate in epidemic subdistricts, Ladyai; Suan Luang; and Jompluak of Samut Songkhram province, Thailand. Settings and Design: Experimental research. Subjects and Methods: We used temephos chemicals from 2 brands: GPO-1 (Temephos 1% W/W Sand Granule) and Zeolite (Temephos 1% W/W Zeolite Granule). First, prepare solutions of GPO-1 and Zeolite into 5 concentrations: 100, 10, 1, 01, and 0.012 ml/L of water. Then, pour 100 ml of each solution into sampling containers for tested Ae. aegypti and 100 ml of distilled water for controlled Ae. aegypti. After that, add 10 larvae in each container, classifying by area. Repeat the experiment in all concentrations 3 times and compared with controlled Ae. aegypti and Bora Bora strain F181 (susceptible strain). Statistical Analysis Used: Calculate data of the death of mosquito larvae at 5 concentrations: 100, 10, 1, 0.1, and 0.012 ml/L to find median lethal concentration (LC50and LC90) and (RR50and RR90) with probit analysis method. Compare average death of mosquito larvae in each subdistrict by Kruskal–Wallis One-way ANOVA, using SPSS software. Results: From the studies, we found that Ae. aegypti in these 3 areas has no resistance against temephos of both brand (RR < 5) and no statistic difference (P < 0.05) among all three subdistricts. Conclusions: Alsthough, there are reports of temephos resistance of mosquito larva in many areas of Thailand, but the results of our study showed no resistance in Samut Songkhram provice. This support is that the mortality of the larvae in experiment groups were not different among control groups. thus, this research result showed that temephos chemical is still an efficient insecticide to eradicate Ae. aegypti in Samut Songkhram province, Thailand.
Keywords: Aedes aegypti, dengue hemorrhagic fever, mosquitoes resistant, temephos resistant
|How to cite this article:|
Chaiphongpachara T, Moolrat L. Insecticide resistance of temephos on Aedes aegypti as dengue vector in Samut Songkhram, Thailand. Ann Trop Med Public Health 2017;10:1439-42
|How to cite this URL:|
Chaiphongpachara T, Moolrat L. Insecticide resistance of temephos on Aedes aegypti as dengue vector in Samut Songkhram, Thailand. Ann Trop Med Public Health [serial online] 2017 [cited 2018 May 23];10:1439-42. Available from: http://www.atmph.org/text.asp?2017/10/6/1439/222636
| Introduction|| |
Dengue hemorrhagic fever is a infectious disease, carried by Aedes aegypti mosquito as a vector and is a world important public health problem, particularly in tropical and subtropical areas including Thailand. Using temephos chemical is a popular method to control this disease. Temephos is an organic phosphate insecticide, chemical name O, O'-(thiodi-4,1-phenylene) bis (O, O'-dimethyl phosphorothioate), in crystal solid, no color, no smell, dissolved by heat or sunlight, and low poisonous to human and mammals. There were reports, indicating that using chemicals can cause a resistance in Ae. aegypti, as well as temephos, which might lead to difficulty in eradicating and controlling Ae. aegypti. The chemical insecticide resistance of mosquito can be divided into two main mechanisms. The first mechanism is the modification of the molecular site targeted and finally is an increased metabolism of the chemical through mutations and/or overexpression of detoxifying enzymes of mosquito.
Samut Songkhram province located in central area of Thailand, divided into three districts: Muang district, Amphawa, and Bangkontee. According to a data of the bureau of epidemiology, it is one of the most infectious areas of dengue hemorrhagic fever in Thailand. In 2014, it has an infectious rate at 101.58/100,000 of its population; this result leads to an attentiveness of related organizations to urgently control an infection, by regularly applying temephos into waterlogged sources. However, this method may lead to the development of mosquito resistant in this province. From the information above, researchers consequently test a chemical resistance of mosquito larva in infected areas in Samut Songkhram, as a primary information to select an appropriate mosquito eradication chemicals in this area.
| Subjects and Methods|| |
Larvae of Ae. aegypti were collected in the most infected subdistricts in each district of Samut Songkhram province, including Ladyai subdistrict, Muang district; Suan Luang subdistrict, Amphawa district; and Jompluak subdistrict, Bangkontee district from Samut Songkhram provincial health office's infection records [Figure 1]. We collected specimen of Ae. aegypti in dense household and population areas from each most infected subdistrict by ovitraps between August and November 2016. Our officials set up 10 ovitraps around selected houses or space under people's houses in each subdistrict. After setting up, we collected Ae. aegypti specimens and sent them to the laboratory of College of Allied Health Sciences (Suan Sunandha Rajabhat University, Thailand).
|Figure 1: Map of Aedes aegypti collection sites in the most infected subdistricts in each district of Samut Songkhram (1 = Ladyai subdistrict, 2 = Suan Luang subdistrict and 3 = Jompluak subdistrict)|
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Examination on insecticide resistance of temephos on Aedes aegypti
We used temephos chemicals from 2 brands: GPO-1 (Temephos 1% W/W Sand Granule) and Zeolite (Temephos 1% W/W Zeolite Granule), which are used popularly in Samut Songkhram Province.
First, prepare solutions of GPO-1 and Zeolite into 5 concentrations: 100, 10, 1, 01, and 0.012 ml/L of water. Then, pour 100 ml of each solution into sampling containers for tested Ae. aegypti and 100 ml of distilled water for controlled Ae. aegypti. After that, add 10 larvae in each container, classifying by area. Repeating the experiment in all concentrations 3 times and compare with controlled Ae. aegypti and Bora Bora strain F181 (susceptible strain). The susceptible strains were kindly provided by Department of Medical Entomology, Faculty of Tropical Medicine, Mahidol University. After 24 h, record and count chemical reactions and death of all tested and controlled mosquito larvae.
Calculate data of the death of mosquito larvae at five concentrations: 100, 10, 1, 0.1, and 0.012 ml/L to find median lethal concentration (LC50 and LC90) and resistance ratio (RR50 and RR90) with probit analysis method. Compare average death of mosquito larvae in each subdistrict by Kruskal–Wallis one-way ANOVA, using SPSS software (version 8.0 for Windows, SPSS Inc., 233 South Wacker Drive, 11th Floor, Chicago, IL 60606-6307). The procedure to calculate an RR is to divide the LC50 of mosquito population by the LC50 of a susceptible strain. When RR is <5, the mosquitoes are considered susceptible, when RR is between 5 and 10, mosquitoes are considered to have moderate resistance, and when RR is >10, the mosquitoes are highly resistant.
| Results|| |
The number of died mosquito larvae classified by temephos chemical and concentration showed that the concentrations of solution at 0.012 and 0.1 mg/L in 3 areas of studies can't be eliminated mosquito larvae. The most concentrated solution of temephos at 100 mg/L of both brands killed all mosquito larvae (10.00 ± 0.00) in all areas. Bora Bora strain, an insecticide susceptible strain, was eradicated at concentration 10 and 100 mg/L as well as tested group and found no death in all controlled group [Table 1].
Mosquito larva from Jompluak subdistrict have a highest number of LC50 of GPO-1, at 34.73, followed by mosquito larva from Ladyai and Suan Luang subdistrict at 30.72 and 24.64 consecutively. The result demonstrates that no mosquito larva from all subdistricts can resist against GPO-1 (RR < 5), one from Jompluak subdistrict has a highest resistant rate at 1.43 after by those from Ladyai and Suan Luang subdistricts at 1.27 and 1.01, respectively. While LC50 of Zeolite Temephos of Suan Luang is the highest at 47.90 than the larva from Jompluak (34.73) and Ladyai (33.74), respectively. The result of RR50 resistance indicates that larva from all areas cannot resist against Zeolite chemical (RR < 5) with 1, 0.73, and 0.70 of Suan Luang, Jompluak, and Ladyai subdistrict, respectively. Comparing the statistic shows no difference of mosquito larva eradication (P > 0.05) by temephos in all areas [Table 2].
|Table 2: Insecticide resistance of Aedes aegypti larvae and difference of mosquito larva eradication in all areas to temephos|
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| Discussion|| |
The research on the resistance of Ae. aegypti as dengue vector to temephos of GPO-1 and Zeolite brands shows that RR is <5 and the death rate was similar to Bora Bora, a susceptible strain, which means tested mosquito larva has no resistance to temephos because there was no profusion use of the chemical in these areas. The resistance occurred from physiological mechanism, a defensive mechanism of hereditary characteristic. Unbounded profusive insecticide usage will expedite a resistance in mosquitoes, requiring more concentrated insecticide or new chemical to eradicate, which causes further problems in controlling this disease.
The collation of temephos eradication efficiency demonstrates that there was no statistic difference in areas of the dengue outbreaks (Ladyai subdistrict, Muang district; Suan Luang subdistrict, Amphawa district; and Jompluak subdistrict, Bangkontee district) of mosquito larva. Thence, temephos insecticide of both brands, GPO-1 and Zeolite, can be used in all areas. Beside using chemicals, there are many interesting methods to eradicate mosquito larva without causing pollutions such as removing all possible mosquito breeding origin, physical control, and biological control.
This research result showed that temephos chemical is still an efficient insecticide to eradicate A. aegypti in Samut Songkhram province, Thailand.
| Conclusions|| |
Although, there are reports of temephos resistance of mosquito larva in many areas of Thailand, but the results of our study showed no resistance in Samut Songkhram provice. This support is that the mortality of the larvae in experiment groups were not different among control groups. thus, this research result showed that temephos chemical is still an efficient insecticide to eradicate Ae. aegypti in Samut Songkhram province, Thailand.
We would like to thank College of Allied Health Science, Suan Sunandha Rajabhat University, Thailand, for their kind support of our research.
Financial support and sponsorship
This study was supported by Suan Sunandha Rajabhat University, Bangkok, Thailand.
Conflicts of interest
There are no conflicts of interest.
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College of Allied Health Sciences, Suan Sunandha Rajabhat University, Bangkok
Source of Support: None, Conflict of Interest: None
[Table 1], [Table 2]