Persistence of DDT, Malathion & Deltamethrin Resistance in Anopheles Culicifacies After Their Sequential Withdrawal from Indoor Residual Spraying in Surat District, India (Dichloro-Diethyl-Trichloroethane) (Report‪)‬

The tropicopolitan mosquito Anopheles culicifacies (Diptera: Culicidae) is the most important vector of malaria in India (1). Gujarat State being highly endemic to malaria, indoor residual spray (IRS) with DDT (dichloro-diethyl-trichloroethane, 1 g/[m.sup.2] and two rounds per year) had been carried out to control An. culicifacies population since 1950s, which though showed spectacular success initially, in due course resulted in widespread resistance in An. culicifacies (2,3). In 1958, DDT was replaced from regular spray by HCH (hexachloro cyclohexane), but was effective only for a short duration as the vector successfully developed high levels of resistance (4). In order to curtail the malaria transmission in Gujarat, organophosphorous insecticide, malathion was introduced for IRS in 1969 (2 g/[m.sup.2] and three rounds per year) (5). Malathion resistance in this species was first reported from Surat in 1973, but its use was continued till mid 1990s and was replaced in 1996 by deltamethrin, a synthetic pyrethroid (0.02 g/[m.sup.2] and two rounds per year) (6). Studies in some villages in District Surat in Gujarat State indicated development of low levels of deltamethrin resistance in 2001 (6). Deltamethrin was withdrawn from IRS in these villages in Surat in 2002 as the annual parasite index (API) became 2 (personal communication 2008; District Malaria Officer, District Surat, Gujarat). The present investigation was carried out to assess the persistence of respective insecticide resistance in field populations of An. culicifacies after sequential withdrawal of DDT, malathion and deltamethrin and to study the resistance/susceptibility pattern in Surat. Material & Methods