Population profile and insecticide resistance in dengue vector Aedes albopictus Skuse in Sarawak, Malaysia / Lau Koon Weng

Lau , Koon Weng (2021) Population profile and insecticide resistance in dengue vector Aedes albopictus Skuse in Sarawak, Malaysia / Lau Koon Weng. PhD thesis, Universiti Malaya.

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Abstract

Dengue fever and dengue hemorrhagic fever infections have caused adverse impact on social function and economic loss in Malaysia till present day. Most studies conducted in Malaysia were focused on Peninsular Malaysia while there are insufficient published literatures related to East Malaysia. Accordingly, the populations of Aedes albopictus from Sarawak were studied to determine their infestation pattern, population structure, and resistance status against major insecticides used for vector control programmes along with the revelation of underlying biochemical resistance mechanism. First and foremost, ovitrap surveillance was conducted in 21 residential areas across 13 districts located in eight divisions in Sarawak State. The ovitrap index (OI) of Aedes larvae was found highest in urban residential area (mean OI = 90.97%), followed by suburban (69.70%), rural (65.45%) and remote (52.63%) residential areas. Interestingly, no Aedes aegypti was observed but two species of Armigeres were found co-breeding with Ae. albopictus. This study suggested that Ae. albopictus was the dominant dengue vector in Sarawak State. The emerged adults were subjected to phylogenetic study based on analyses of the mitochondrial COI gene. The analysis revealed twenty two haplotypes from 120 samples and the haplotypes were widely distributed across all the populations. Adult and larval bioassays were performed according to the WHO standard protocols to assess knockdown and mortality rate of Ae. albopictus. Only cyfluthrin was able to inflict complete knockdown but different susceptibility patterns were observed in other adulticides. For mortality rates, adult Ae. albopictus was susceptible to cyfluthrin and dieldrin. Significant correlations were found within pyrethroid and carbamates classes. This study revealed that cyfluthrin was effective against Aedes mosquito control in Sarawak. For larval bioassay, Ae. albopictus larvae were completely susceptible to bromophos and temephos (mortality = 100%), and highly resistant to DDT, chlorpyrifos and malathion (mortality ranged from 0 – 20%). However, the larvae showed various levels of susceptibility to dieldrin, fenitrothion and fenthion. Generally, bromophos and temephos were still effective to control Ae. albopictus larvae in Sarawak. Enzyme assay was conducted to reveal the underlying biochemical mechanism which caused insecticide resistance. The results revealed that there were elevated α-esterases and β-esterases activities in three populations at adult and four populations in larval Ae. albopictus but no significant elevation of enzyme activities in mixed function oxidases (MFO) and glutathione-S-transferases (GST) among the populations. Acetylcholinsterase was insensitive to propoxur in adult Ae. albopictus from Sarikei and larval stage from Dalat. Moreover, association between activities of α-esterases and β-esterases, α-esterases and acetylcholinesterase, and β-esterases and acetylcholinesterase were also demonstrated. The efficacy of five insect growth regulators (IGRs) as alternative control agents against Ae. albopictus was also determined. Field populations of Ae. albopictus were susceptible to methoprene, pyriproxyfen, cyromazine and novaluron, but tolerance towards diflubenzuron. In summary, periodical monitoring of insecticide effectiveness is important to prevent development of resistance since chemical control remains as crucial approach in vector control programme. This study also suggested that IGR could possibly be an alternative selection to replace conventional insecticides.

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