Medical and Veterinary Entomology (2007) 21, 97–102 © 2007 The Authors Journal compilation © 2007 The Royal Entomological Society 97 Introduction Anopheles arabiensis Patton is a member of the Anopheles gambiae Giles complex and the third most important malaria vector mosquito in Africa (Gillies & Coetzee, 1987). Insecticide resistance in this species based on the W.H.O. susceptibility tests, has been reported from West Africa [dichlorodiphenyl- trichloroethane (DDT), dieldrin, Brown, 1986], southern Africa [dieldrin/benzenehexachloride (BHC), Green, 1982; DDT, Hargreaves et al., 2003], Sudan (malathion, DDT, dieldrin, per- methrin, Hemingway, 1983) and the Indian Ocean islands of Madagascar (dieldrin) and Mauritius (DDT) (Brown, 1986). Two primary mechanisms of DDT resistance have been iden- tified in malaria vector mosquitoes: (1) significant metabolic detoxification based on increased activity of glutathione- S- transferase (GST) described in Anopheles gambiae Giles s.s. (Ranson et al., 2000a) and apparently operational in southern African Anopheles arabiensis (Hargreaves et al., 2003); (2) tar- get site insensitivity, referred to as knockdown resistance ( kdr), shown to confer significant resistance to DDT and pyrethroid insecticides in An. gambiae s.s. (henceforth referred to as An. gambiae) in West Africa (Martinez-Torres et al., 1998). DDT and pyrethroids share the same mode of action on the nerv- ous system, targeting the neuronal voltage-gated sodium ion Insecticide resistance in the malarial mosquito Anopheles arabiensis and association with the kdr mutation T. S. MATAMBO 1,3 , H. ABDALLA 1,3,5 , B. D. BROOKE 1,2 , L. L. KOEKEMOER 1,2 , A. MNZAVA 4 , R. H. HUNT 1,3 and M. COETZEE 1,2 1 Vector Control Reference Unit, National Institute for Communicable Diseases, NHLS, Sandringham, Johannesburg, South Africa, 2 Division of Virology and Communicable Diseases Surveillance, School of Pathology of the National Health Laboratory Service and the University of the Witwatersrand, Johannesburg, South Africa, 3 School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa, 4 World Health Organization, Eastern Mediterranean Region, Cairo, Egypt and 5 Blue Nile Research and Training Institute, Wad Medani, Gezira, Sudan Abstract. A colony of Anopheles arabiensis Patton (Diptera: Culicidae) from the Sennar region of Sudan was selected for resistance to dichlorodiphenyltrichloroethane (DDT). Adults from the F-16 generation of the resistant strain were exposed to all four classes of insecticides approved for use in malaria vector control and showed high levels of resistance to them all (24-h mortalities: malathion, 16.7%; bendiocarb, 33.3%; DDT, 12.1%; dieldrin, 0%; deltamethrin, 24.0%; permethrin, 0%). Comparisons between the unselected base colony and the DDT-resistant strain showed elevated glutathione- S- transferase ( P < 0.05) in both sexes and elevated esterases ( P < 0.05) in males only. The Leu-Phe mutation in the sodium channel gene was detected by polymerase chain reaction and sequencing, but showed no correlation with the resistant phenotype. These results do not provide any explanation as to why this colony exhibits such widespread resistance and further studies are needed to determine the precise mechanisms involved. The implications for malaria vector control in central Sudan are serious and resistance management (e.g. through the rotational use of different classes of insecticides) is recommended. Key words. Anopheles arabiensis, carbamates, DDT, insecticide resistance, kdr mutation, organophosphates, pyrethroids, Sudan. Correspondence: Professor M. Coetzee, Vector Control Reference Unit, NICD, Private Bag X4, Sandringham 2131, South Africa. Tel.: +2711 386 6480; Fax: +2711 386 6481; E-mail: maureenc@nicd.ac.za