The surveillance and resistance status of Aedes mosquitoes against insect growth regulators in Malaysia / Lau Koon Weng

Lau, Koon Weng (2012) The surveillance and resistance status of Aedes mosquitoes against insect growth regulators in Malaysia / Lau Koon Weng. Masters thesis, University of Malaya.

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Abstract

Dengue is the most important mosquito-borne disease in Malaysia and the principal vector of dengue are Aedes aegypti and Aedes albopictus. Little information was available of Insect growth regulators (IGRs) in Malaysia. This study was attempted to (1) determine the distribution and abundance of Aedes mosquitoes in multiple storey buildings in Selangor and Kuala Lumpur; (2) evaluate the susceptibility status of nationwide collected Aedes mosquitoes against IGRs; and (3) investigate the residual efficacy of IGRs in indoor and outdoor conditions. The vertical distribution and abundance of Aedes mosquitoes were determined in 4 high rise apartments located in Selangor [Kg. Baiduri (KB)] and Kuala Lumpur [Student Hostel of University of Malaya (UM), Kg. Kerinchi (KK) and Hang Tuah (HT)] using ovitrap surveillance. The results implied that Aedes mosquitoes could be found from ground floor to highest floor of multiple storey buildings but no significant difference was found. Ovitrap indices obtained from all sites were 8.33 to 69.09%. Aedes aegypti and Ae. albopictus were found breeding in HT, KK and KB; while only Ae. albopictus was obtained from UM. The study suggests that the invasion of Aedes mosquitoes in high-rise apartments could enhance the transmission of dengue virus, and approach on vector control in this type of residential areas should be developed. The susceptibility status of Ae. aegypti and Ae. albopictus obtained from 12 states in Malaysia was evaluated against 5 insect growth regulators, namely pyriproxyfen, methoprene, diflubenzuron, cyromazine and novaluron according to the protocol by WHO published in 1981. Field populations of Ae. aegypti exhibited moderate and low resistance against methoprene (Resistance Ratio, RR = 12.65) and pyriproxyfen (RR = 1.35), respectively; and susceptible to diflubenzuron, cyromazine and novaluron. On the other hand, field populations of Ae. albopictus only exhibited low resistance against diflubenzuron (RR = 2.08) and susceptible to other tested IGRs. Although field populations of Aedes mosquitoes have developed some degree of resistance toward certain groups of IGRs such as methoprene, pyriproxyfen and diflubenzuron; cyromazine and novaluron still provide promising effect towards field populations of Ae. aegypti and low resistance was shown for populations of Ae. albopictus from several states. The use of IGRs should be considered as an alternative control agent when larvae had developed resistance to conventional insecticides. The residual activities of 5 insect growth regulators (IGRs) were studied and compared to operational dosage of temephos (1 mg/L) and Bacillus thuringiensis israelensis (Bti) (0.008 mg/L). The IGRs, temephos and Bti were introduced into plastic containers containing 5 litres of water. Thirty Aedes aegypti larvae were added into each container weekly. The indicators of effectiveness of each control agent for these studies were duration of effectiveness of each dosage and the percentage of emergence inhibition (EI). An end-point of EI/mortality ≥ 50% was considered to be effective. Pyriproxyfen possessed the longest residual activity in both indoor (43 weeks) and outdoor (26 weeks) conditions, followed by temephos (26 weeks in indoor and 16 weeks in outdoor). The residual activity of Bti in indoor lasted 8 weeks which was longer than cyromazine and diflubenzuron; however, it was least effective in outdoor, lasting only 2 weeks. This study revealed that pyriproxyfen possessed good residual effect among five IGRs when compared to temephos and Bti. The use of IGRs can be an alternative long-term control measure against dengue vector mosquitoes in stagnant waters.

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