Transactions of the Royal Society of Tropical Medicine and Hygiene (2009) 103, 1139—1145 available at www.sciencedirect.com journal homepage: http://www.elsevier.com/locate/trstmh Evidence of multiple pyrethroid resistance mechanisms in the malaria vector Anopheles gambiae sensu stricto from Nigeria T.S. Awolola a,* , O.A. Oduola a , C. Strode b , L.L. Koekemoer c,d , B. Brooke c,d , H. Ranson b a Nigerian Institute of Medical Research, Yaba, Lagos, Nigeria b Liverpool School of Tropical Medicine, Liverpool, UK c Vector Control Reference Unit, National Institute for Communicable Diseases, Johannesburg, South Africa d Division of Virology and Communicable Disease Surveillance, School of Pathology of the National Health Laboratory Service and the University of the Witwatersrand, Johannesburg, South Africa Received 17 April 2008; received in revised form 15 August 2008; accepted 15 August 2008 Available online 30 September 2008 KEYWORDS Anopheles; Malaria; Metabolism; Pyrethroid; Insecticide resistance; Nigeria Summary Pyrethroid insecticide resistance in Anopheles gambiae sensu stricto is a major con- cern to malaria vector control programmes. Resistance is mainly due to target-site insensitivity arising from a single point mutation, often referred to as knockdown resistance (kdr). Metabolic- based resistance mechanisms have also been implicated in pyrethroid resistance in East Africa and are currently being investigated in West Africa. Here we report the co-occurrence of both resistance mechanisms in a population of An. gambiae s.s. from Nigeria. Bioassay, synergist and biochemical analysis carried out on resistant and susceptible strains of An. gambiae s.s. from the same geographical area revealed >50% of the West African kdr mutation in the resis- tant mosquitoes but <3% in the susceptible mosquitoes. Resistant mosquitoes synergized using pyperonyl butoxide before permethrin exposure showed a significant increase in mortality com- pared with the non-synergized. Biochemical assays showed an increased level of monooxygenase but not glutathione-S-transferase or esterase activities in the resistant mosquitoes. Microarray analysis using the An. gambiae detox-chip for expression of detoxifying genes showed five over- expressed genes in the resistant strain when compared with the susceptible one. Two of these, CPLC8 and CPLC#, are cuticular genes not implicated in pyrethroid metabolism in An. gambiae s.s, and could constitute a novel set of candidate genes that warrant further investigation. © 2008 Royal Society of Tropical Medicine and Hygiene. Published by Elsevier Ltd. All rights reserved. ∗ Corresponding author. Present address: Medical Research Council Laboratories, The Gambia, P.O. Box 273, Banjul, The Gambia. Tel.: +220 702 2832; fax: +220 449 7952. E-mail addresses: awololas@hotmail.com, tsawo2001@yahoo.co.uk (T.S. Awolola). 0035-9203/$ — see front matter © 2008 Royal Society of Tropical Medicine and Hygiene. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.trstmh.2008.08.021