Review of Temephos Discriminating Concentration for Monitoring the Susceptibility of Anopheles labranchiae (Falleroni, 1926), Malaria Vector in Morocco
In Morocco, the resistance monitoring of Anopheles labranchiae larvae to temephos is done using discriminating concentration of 0.125？mg, which is half of the WHO recommended dose for Anopheles. However, this dosage seemed to be too high to allow an early detection of the resistance and its revision was found necessary. The present study was carried out during May-June 2008 and 2009 in nine provinces from the north-west of the country. The aim was to determine the lethal concentrations LC100 of temephos for the most susceptible populations and to define the discriminating dosage as the double of this value. The bioassays were conducted according to WHO standard operating protocol to establish the dose-mortality relationship and deduct the LC50 and LC95. The results of this study indicated that the LC100 obtained on the most susceptible populations was close to 0.05？mg/L. Therefore, the temephos discriminating dosage for susceptibility monitoring of An. labranchiae larvae in Morocco was set to be 0.1？mg/L. 1. Introduction In Morocco, last autochthonous malaria case was registered in 2004. Since then a vector control program was established to prevent a possible return of malaria transmission. It is mainly based on the larval control of the main vector: Anopheles labranchiae (Falleroni 1926) [1]. This control includes integrated management using environmental methods and larvivorous fish (Gambusia holbrooki) as biological control. Insecticides are used as the last option but they take an important place in the National Malaria Control Programme (NMCP). Larval treatments started in the 1950’s using DDT [2]. In 1978, an organophosphate insecticide, the temephos (Abate 500 EC) was introduced, and since then, it has been the only insecticide used for An. labranchiae larval control. The monitoring of An. labranchiae susceptibility to insecticides used in larval and adult control is an essential component of the NMCP. This activity has started with the launch of the programme following WHO protocol, using discriminating dosage [3]. The first susceptibility tests of Anopheles labranchiae to temephos were carried out before its introduction for larval control using concentrations supplied by WHO (0.005, 0.025, 0.125, 0.625？mg/L). Results of these tests, carried out on natural populations, showed that the lowest dosage involving regularly 100% mortality was 0.125？mg/L. This concentration was considered as a specific discriminating dose for Moroccan An. labranchiae and was used in routine resistance monitoring. Although this dose represents half of the diagnostic
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