ORIGINAL PAPER Effect of temperature on development, eclosion, longevity and survivorship of malathion-resistant and malathion-susceptible strain of Culex quinquefasciatus V. Swain & R. K. Seth & S. S. Mohanty & K. Raghavendra Received: 8 March 2008 / Accepted: 17 March 2008 / Published online: 15 April 2008 # Springer-Verlag 2008 AbstractDensity of vectors and development of resistance against insecticides are two important aspects in the control of vector-borne diseases. Here,effectof temperature on different aspects of development of malathion-resistant and susceptible strains of Culex quinquefasciatus was evaluated in the laboratory. Fourth-instar larvae of C. quinquefascia- tus were exposed to 37°C, 39°C, 40°C, and 41°C, and their LT 50 valuescalculated. The fourth-instar larvaewere subjected to heat for 4 h at 39°C and live larvae were reared until the completion of life cycle.The larvae of malathion-resistant strain were more tolerant to hea than the larvae of malathion-susceptible ones. The difference in mortality between 37°C, 39°C, 40°C, and 41°C of both the strainsof C. quinquefasciatus werehighly significant. Pupation percentage of heat-exposed larvae of both the strains was higher and delayed than the control ones.The percentage of adultemergence from the heat-exposed larvae was significantly lower than the control. The adult femaleof malathion-resistant strainshowedincreased longevity when exposed to heat atlarvalstage but reverse was true in case of malathion-susceptible. The highlights of the study would help in the management of resistance of mosquito vectors in the tropicswhere variable climatic condition is observed. Introduction Culexquinquefasciatus is a majorvectorof lymphatic filariasisin the tropicsand also actsas an annoying pest.Insecticide resistance in vector-borne diseases is a majorpublichealthconcern.The widespreaduse of organophosphorus and otherinsecticides for filariasis and malaria control hasresulted in the development of high levels of resistance in many areas (Hemingway and Karunaratne 1998). C. quinquefasciatus adults were resis- tantto Dichlorodiphenyltrichloroethane, dieldrin,malathi- on, and fenitrothion in India since long (Thavaselvam et al 1993).The adaptability of resistance in insect varies with ecological changes including thermal adaptation (Patil et a 1996). Geographical expansion of vector-borne diseases in several continents has been partially associated to changes in globalwarming (Githeko et al. 2000).Most of such diseases are transmitted by mosquitoes, whose develop- mental cycle is affected by temperature (Rueda et al. 199 Temperature has a major effecton the rate at which the immature stages of insects develop into adults (Lassiter e al. 1995).In hot tropicalclimaticsituations, maximum temperatures occur in pools of groundwater for only short periods each day (Swain et al. 2008), so it is important for larvae that occupy habitats exposed to full tropical sunligh to be able to survive brief exposure to extremely high temperatures. Although mosquito populations are predom- inantly numerous in tropical areas with average temperatu ranging from 25°C to 35°C (Dixit et al. 2002), there are no data on how malathion-resistant and susceptible strains of C. quinquefasciatus face temperature variation on the Indian subcontinent. The density ofC. quinquefasciatus was lowered during summer and winter (Dixit et al. 2002; Parasitol Res (2008) 103:299–303 DOI 10.1007/s00436-008-0969-5 V. Swain (*) : R. K. Seth Department of Zoology, University of Delhi, Delhi 110007, India e-mail: vijaylakshmi.swain@rediffmail.com S. S. Mohanty : K. Raghavendra National Institute of Malaria Research, 22-Sham Nath Marg, Delhi 110054, India