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Objective: To assess the insecticide susceptibility status of Anopheles cracens (An. cracens) and Anopheles maculatus (An. maculatus) from knowlesi malaria endemic areas in Peninsular Malaysia towards DDT, malathion and deltamethrin and to determine the resistance mechanism involved. Methods: Adult and larval mosquitos were collected for surveillance. Susceptibility status of Anopheles was determined using the standard WHO adult bioassay, larval bioassay and biochemical enzyme assay. Results: WHO adult bioassay results indicated An. cracens collected from Kampung Sungai Ular, Pahang was resistant towards 4% DDT, while An. maculatus collected from Kampung Sokor, Kelantan and Kampung Sungai Lui, Selangor exhibited resistance towards 4% DDT. However, the enzyme activity profiles varied according to strains and species. The resistance ratio of larval bioassay, showed that all strains and species tested were susceptible to malathion and temephos. Conclusions: Since only a few anopheline strains exhibited low level of insecticide resistance towards malathion, DDT and temephos. These insecticides are still considered effective for vector control program towards An. cracens and An. maculatus.
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Objective: To assess the insecticide susceptibility status of Anopheles cracens (An. cracens) and Anopheles maculatus (An. maculatus) from knowlesi malaria endemic areas in Peninsular Malaysia towards DDT, malathion and deltamethrin and to determine the resistance mechanism involved. Methods: Adult and larval mosquitos were collected for surveillance. Susceptibility status of Anopheles was determined using the standard WHO adult bioassay, larval bioassay and biochemical enzyme assay. Results: WHO adult bioassay results indicated An. cracens collected from Kampung Sungai Ular, Pahang was resistant towards 4% DDT, while An. maculatus collected from Kampung Sokor, Kelantan and Kampung Sungai Lui, Selangor exhibited resistance towards 4% DDT. However, the enzyme activity profiles varied according to strains and species. The resistance ratio of larval bioassay, showed that all strains and species tested were susceptible to malathion and temephos. Conclusions: Since only a few anopheline strains exhibited low level of insecticide resistance towards malathion, DDT and temephos. These insecticides are still considered effective for vector control program towards An. cracens and An. maculatus.
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Objective: To investigate the susceptibility to temephos, permethrin and deltamethrin of Aedes aegypti (. Ae. aegypti), collected from areas with high incidence of dengue hemorrhagic fever cases in Phitsanulok Province, Thailand. Methods: The F1 progenies of Ae. aegypti colony, originated from five sub-districts including Aranyik, Hua Ro, Nai Muang, Ban Krang and Tha Pho, were used in the bioassays following the procedures of World Health Organization. For larval bioassay, the late third or early fourth-instar larvae were tested with different concentrations of temephos. For adult bioassay, the females were exposed to 0.75 % permethrin or 0.05% deltamethrin. LC50 value and mortality rate were analyzed to compare the insecticide susceptibility of the larvae and the adults in each area, respectively. Results: The LC50 value of temephos for the larvae from Aranyik, Hua Ro, Nai Muang, Ban Krang and Tha Pho sub-districts was 0.017, 0.017, 0.026, 0.061, and 0.113 ppm, respectively. For permethrin, the highest mortality rate (86.84%) was found in the mosquitoes from Aranyik but the others were more resistant with the lower mortality rates (16.00-42.67%). The adult mortality rates after exposing to deltamethrin were higher (82.34-98.67%) in all areas. Conclusions: Ae. aegypti larvae were still susceptible to temephos. Conversely, most tested adults tended to resist the permethrin and deltamethrin.
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OBJECTIVE@#To investigate the susceptibility to temephos, permethrin and deltamethrin of Aedes aegypti (Ae. aegypti), collected from areas with high incidence of dengue hemorrhagic fever cases in Phitsanulok Province, Thailand.@*METHODS@#The F1 progenies of Ae. aegypti colony, originated from five sub-districts including Aranyik, Hua Ro, Nai Muang, Ban Krang and Tha Pho, were used in the bioassays following the procedures of World Health Organization. For larval bioassay, the late third or early fourth-instar larvae were tested with different concentrations of temephos. For adult bioassay, the females were exposed to 0.75 % permethrin or 0.05% deltamethrin. LC50 value and mortality rate were analyzed to compare the insecticide susceptibility of the larvae and the adults in each area, respectively.@*RESULTS@#The LC50 value of temephos for the larvae from Aranyik, Hua Ro, Nai Muang, Ban Krang and Tha Pho sub-districts was 0.017, 0.017, 0.026, 0.061, and 0.113 ppm, respectively. For permethrin, the highest mortality rate (86.84%) was found in the mosquitoes from Aranyik but the others were more resistant with the lower mortality rates (16.00-42.67%). The adult mortality rates after exposing to deltamethrin were higher (82.34-98.67%) in all areas.@*CONCLUSIONS@#Ae. aegypti larvae were still susceptible to temephos. Conversely, most tested adults tended to resist the permethrin and deltamethrin.
ABSTRACT
Objective:To investigate the susceptibility to temephos, permethrin and deltamethrin ofAedes aegypti(Ae. aegypti), collected from areas with high incidence of dengue hemorrhagic fever cases inPhitsanulokProvince,Thailand.Methods:TheF1 progenies ofAe. aegypti colony, originated from five sub-districts includingAranyik,HuaRo,NaiMuang,BanKrang andThaPho, were used in the bioassays following the procedures ofWorldHealthOrganization.For larval bioassay, the late third or early fourth-instar larvae were tested with different concentrations of temephos. For adult bioassay, the females were exposed to0.75% permethrin or0.05% deltamethrin.LC50 value and mortality rate were analyzed to compare the insecticide susceptibility of the larvae and the adults in each area, respectively. Results:TheLC50 value of temephos for the larvae from Aranyik,HuaRo,NaiMuang,BanKrang andThaPho sub-districts was0.017,0.017,0.026,0.061, and0.113 ppm, respectively.For permethrin, the highest mortality rate(86.84%) was found in the mosquitoes fromAranyik but the others were more resistant with the lower mortality rates(16.00-42.67%).The adult mortality rates after exposing to deltamethrin were higher(82.34-98.67%) in all areas.Conclusions:Ae. aegypti larvae were still susceptible to temephos.Conversely, most tested adults tended to resist the permethrin and deltamethrin.
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Background & objectives: Updating information on response (susceptible / resistant status) of vectors to the insecticides in use is essential to formulate and introduce appropriate resistance management strategy. Therefore, a study was undertaken in the 10 southern districts of Odisha State, which are endemic for Plasmodium falciparum malaria, to determine the insecticide susceptibility/ resistance status of Anopheles fluviatilis and An. culicifacies, the vectors of malaria. Methods: Mosquitoes were collected during September 2010 - February 2012 from 60 randomly selected villages in the 10 districts and blood-fed females were exposed to the diagnostic dosage of DDT (4.0%), malathion (5.0%) and deltamethrin (0.05%) for one hour. Mortality was recorded at 24 h after the exposure. The test mortality was corrected to the control mortality. Results: An. fluviatilis was susceptible to the three insecticides tested while, An. culicifacies was resistant to DDT and malathion in all the 10 districts except in two, where its response against malathion was under ‘verification required’ category. Against deltamethrin, An. culicifacies was susceptible in two districts; while in the other eight districts its response was under ‘verification required’ category. Interpretation & conclusions: Since An. fluviatilis the vector species primarily associated with transmission of malaria, was still susceptible to DDT, indoor residual spraying with DDT could be continued in the 10 districts. Also, in view of the large scale implementation of long lasting insecticidal nets and the signs of development of resistance in An. culicifacies to deltamethrin, response of the vectors to synthetic pyrethroids needs to be periodically monitored.
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Background: Dengue is rapidly becoming established in north-east India and spreading, on account of rapid urbanization and population movement, with reported morbidity and attributable death cases. This study aims to determine the seasonal abundance of Aedes (Stegomyia) albopictus and Aedes (Stegomyia) aegypti in Guwahati metropolis and suburban settlements; to characterize the breeding resources for these mosquitoes; and to ascertain the status of their susceptibility to adulticides and larvicides. Methods: Mosquito larval surveys were carried out in different localities in both Guwahati city and adjoining suburbs from January to December 2013, to determine the seasonal abundance of disease vectors and their breeding preferences. The insecticide susceptibility status of mosquito adults and larval populations of both Aedes aegypti and Aedes albopictus was ascertained, using World Health Organization standard diagnostic concentrations and test procedures. Results: The study revealed that both Aedes aegypti and Aedes albopictus are widely abundant in Guwahati city and suburbs, and breeding in a wide variety of resources. Aedes albopictus, however, was the predominant mosquito species in suburbs, breeding preferentially in flower vases, cut-bamboo stumps and leaf axils. Aedes aegypti was the most common in the city, breeding predominantly in discarded tyres, cement tanks and used battery boxes. Both Aedes aegypti and Aedes albopictus were resistant to dichlorodiphenyltrichloroethane (DDT; 4%), but susceptible to malathion (5%), and exhibited a varied response to pyrethroids. However, larval populations of both these mosquito species were susceptible to larvicides, including malathion (1.0 mg/L), temephos (0.02 mg/L) and fenthion (0.05 mg/L), at much lower dosages than diagnostic concentrations. Conclusion: Given the seasonal abundance and case incidence in city areas, it is highly probable that Aedes aegypti is the predominant mosquito vector transmitting dengue virus. The study results have direct relevance for the state dengue-control programme, for targeting interventions and averting outbreaks and spread of disease.
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A susceptible strain of Aedes albopictus derived from the Gainesville strain (Florida, USA) was established in our laboratory. The larvicidal efficacies of the neurotoxic insecticides temephos, permethrin and the pure cis and trans-permethrin isomers and the microbial insecticide Bacillus thuringiensis israelensis (Bti) against Ae. albopictus were estimated and compared to a susceptible strain of Aedes aegypti. The larvicidal effect of insect growth regulator pyriproxyfen was also evaluated in both mosquito strains. The median lethal concentration/median emergency inhibition values for Ae. aegypti and Ae. albopictus, respectively, were: temephos, 3.058 and 6.632 ppb, permethrin, 3.143 and 4.933 ppb, cis-permethrin, 4.457 and 10.068 ppb, trans-permethrin, 1.510 and 3.883 ppb, Bti, 0.655 and 0.880 ppb and pyriproxyfen, 0.00774 and 0.01642 ppb. Ae. albopictus was more tolerant than Ae. aegypti to all six larvicides evaluated. The order of susceptibility for Ae. aegypti was pyriproxyfen > Bti > trans-permethrin > temephos > permethrin > cis-permethrin and for Ae. albopictus was pyriproxyfen > Bti > trans-permethrin > permethrin > temephos > cis-permethrin. Because both species can be found together in common urban, suburban and rural breeding sites, the results of this work provide baseline data on the susceptibility of Ae. albopictus to insecticides commonly used for controlling Ae. aegypti in the field.