A statewide insecticide resistance monitoring study in Sabah, Malaysia: A special focus on Aedes albopictus / Nur Elia Amira Mohd Roslin

Nur Elia Amira , Mohd Roslin (2024) A statewide insecticide resistance monitoring study in Sabah, Malaysia: A special focus on Aedes albopictus / Nur Elia Amira Mohd Roslin. PhD thesis, Universiti Malaya.

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Abstract

Insecticide resistance in Aedes is rampant in Malaysia, as dengue management largely relies on the usage of insecticides. Despite being the fifth state with the highest dengue incidence in Malaysia, study on insecticide resistance among Aedes is very scarce in Sabah, Malaysia. Consequently, a statewide study was conducted there to (1) investigate the insecticide susceptibility status of Aedes albopictus larvae and adults, (2) reevaluate the World Health Organization (WHO)-recommended diagnostic dosages of larvicides, (3) characterize the biochemical and molecular mechanisms in relation to insecticide resistance, (4) evaluate the efficacy of insect growth regulators (IGRs) and (5) assess the level of knowledge, attitude and practice (KAP) concerning dengue control among local communities. WHO larval bioassays indicated that chlorpyrifos and fenthion were the two most potent organophosphates. As for organochlorine larvicides, all populations showed complete susceptibility towards dieldrin but resistant toward dichlorodiphenyltrichloroethane (DDT). In WHO adult bioassays, only pyrethroids were able to cause 100.00% knockdown to Ae. albopictus. In regard to mortality rate, Ae. albopictus adults were mostly susceptible towards all pyrethroids, dieldrin, and malathion, but exhibited resistance towards bendiocarb, propoxur, DDT and fenitrothion. Correlation analysis demonstrated cross-resistance between bendiocarb and propoxur; and malathion and propoxur. In the reevaluation of the WHO-recommended diagnostic dosages of larvicides, all insecticides except dieldrin displayed various folds of increment. DDT exhibited the highest increment in comparison to prior dosage, while fenthion showed the least dosage increment. Bioassays using the newly revised diagnostic dosages revealed that majority of the populations were susceptible against most organophosphates, dieldrin and permethrin; but resistant against DDT and propoxur. In biochemical assays, Ae. albopictus larvae recorded significant increment in both Non-Specific Esterases (EST) activities, while adults displayed significant increment in Mixed Function Oxidases (MFO) and Acetylcholinesterase (AChE) activities. The remaining activity of AChE post propoxur intervention indicated that majority of the larval populations comprised homozygous resistant (RR) genotype whereas most adults comprised heterozygous (RS) genotype. Correlation analysis revealed significant correlations in most survivability rates of organophosphate larvicides against ESTs and MFOs activities, while survivability rates of adulticides were significantly correlated with MFO, β-EST and AChE activities. In molecular assay, a subset of samples from each population were screened for kdr resistance alleles, but no point mutations were detected. Efficacy evaluation of IGRs against Ae. albopictus larvae showed that all populations were susceptible towards all IGRs used. A cross sectional survey conducted on local communities in Sabah revealed economic factors as final independent predictor in all KAP domains. KAP parameters were correlated with each other, but wide gaps between the scores implied that good attitude was not translated into either good knowledge or practice. In short, as this study pioneer a statewide insecticide evaluation study in Sabah, Malaysia, the findings could serve as a baseline reference for health authorities in formulating an effective vector control plan, be it in deciding effective insecticide dosage, considering other alternative (IGRs) or executing a better dengue control educational program that could have wider reachability.

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