UMTAS 2011 Empowering Science, Technology and Innovation Towards a Better Tomorrow 202 LSO37 Insecticide Susceptibility Status of Culex Quinquefasciatus Larvae Obtained From Perak, Terengganu and Kelantan, Malaysia V.L. Low 1* , C.D. Chen 1 , H.L. Lee 2 , C.S. Leong 1 , K.H.M. Chia 1 and M. Sofian- Azirun 1 1 Institute of Biological Sciences, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia, 2 Medical Entomology Unit, WHO Collaborating Centre for Vectors, Institute for Medical Research, Jalan Pahang, 50588 Kuala Lumpur, Malaysia *Corresponding author’s e-mail: lucaslow24@gmail.com Keywords: Culex quinquefasciatus, larval bioassay, insecticide resistance, Malaysia Introduction Culex quinquefasciatus Say, a species of blood-feeding mosquito of the family Culicidae which is commonly known as the pantropical pest and urban vector of Bancroftian filariasis [1]) and St. Louis encephalitis virus [2]. In Malaysia, Culex quinquefasciatus is a potential vector of bancroftian filariasis in the near future [3]. In order to prevent the outbreak of disease transmission of these nuisance mosquito, insecticide application remains as the main control agents against mosquito vectors. However, repeated use of the same insecticide could contribute to the occurrence of insecticide resistance. Therefore, newer residual insecticides such as organophosphates and pyrethroids have been introduced as alternatives to chlorinated hydrocarbon insecticides (DDT) [4]. As the indicator of the insecticide efficiency, the susceptibility status of mosquitoes against insecticides should be evaluated from time to time for a better insecticide resistance management and pest control. The aim of this study is to detect the malathion and permethrin resistance in Culex quinquefasciatus collected from Perak, Terengganu and Kelantan, Malaysia. Materials and Methods Specimen collection Mosquito larvae were collected from high organic stagnant water in Sitiawan (Perak), Kuala Terengganu (Terengganu) and Kota Bharu (Kelantan) by dipping method. Insecticides Two groups of insecticide used in the larvae susceptibility test were organophosphate (malathion) and pyrethroid (permethrin). The insecticide solutions were prepared by WHO Collaborating for Vectors in Universiti Sains Malaysia, Penang. Insecticide susceptibility test This test was conducted according to WHO larval susceptibility bioassay procedure [5]. The bioassay was conducted in disposable plastic cups of 300ml capacity. Twenty-five late third or early fourth instar larvae were introduced into the plastic cups. Each insecticide consisted of five different concentrations with serial dilution. The prepared stock solution of insecticide was added into 150ml deionized tap water which was kept overnight. After