Insecticide Resistance And Its Underlying Mechanisms In Field Populations Of Aedes Aegypti (Diptera: Culicidae) In Singapore, And Laboratory And Field Evaluation Of Pyriproxyfen 0.5g
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Date
2017-02
Authors
Koou, Sin Ying
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Publisher
Universiti Sains Malaysia
Abstract
This study covered the use of bioassay method, synergists, biochemical assays and molecular technique to identify the insecticide susceptibility in seven field populations of Ae. aegypti in Singapore, and to investigate its underlying mechanisms. Bioassays revealed different levels of resistance to pyrethroids (deltamethrin, cypermethrin, permethrin and etofenprox) and susceptibility to organophophates (temephos and pirimiphos-methyl) and Bti. The insecticide susceptibility profile of Ae. aegypti was found to be homogeneous among the different study sites. Further study also demonstrated that resistance remains stable across five years, suggesting that resistance trait remains fixed in field populations for long time. The addition of synergists generally failed to enhance the toxicity of the insecticides investigated, suggesting an insignificant role of metabolic-based resistance. Further biochemical investigation of specific metabolic enzyme activities suggested that detoxifying enzymes, mono-oxygenases, esterases, glutathione S-transferases and altered acetylcholinesterases generally did not contribute to the resistance observed. The prevalence of pyrethroid resistance in Ae. aegypti opulations is significantly inferred by the knockdown resistance (kdr) mechanism. Molecular assay revealed the presence of kdr mutations, S989P, V1016G and F1534C in resistant-strains of Ae. aegypti. Most (77%) individuals possessed F1534C mutation, reflecting the wide distribution of this mutation in field populations of Ae. aegypti. In view of pyrethroid resistance among the Ae. aegypti populations, the use of pyriproxyfen could be a useful larvicide for Aedes control. Results showed that pyriproxyfen is effective against Aedes mosquitoes for at least one month even after exposure to direct sunlight and rain. Insecticide resistance management is crucial especially given the limited number of registered insecticide classes available for vector control. Furthermore, the management of insecticide resistance is complicated by resistance in a variety of forms. Although the results of this study provide basic requirements on a guide in the use of chemicals for operational control of Ae. aegypti, continuous monitoring and insecticide screening are needed for sustainable resistance management.
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Keywords
Use of bioassay method , to identify the insecticide susceptibility