ROTATIONAL AND MOSAIC STRATEGIES FOR DELAYING THE DEVELOPMENT OF INSECTICIDE RESISTANCE IN MOSQUITOES - BASELINE DATA FOR A LARGE SCALE FIELD TRIAL IN SOUTHERN MEXICO

Abstract:
A large scale resistance management programme is currently being undertaken in Chiapas, Southern Mexico. this paper reports the baseline levels of resistance as detected by bioassays and biochemical assays in the mosquito Anopheles albimanus in the study area. A high level of resistance to DDT and low levels of organophosphorus, carbamate and pyrethroid resistance were detected by WHO discriminating dose assays in field populations of An. albimanus in the region this resistance management project is being undertaken. Biochemical assays showed that the DDT resistance was caused by elevated levels of GST activity leading to increased rates of metabolism of DDT to DDE. The numbers of individuals with elevated GST and DDT resistance were well correlated, suggesting that this is the only major DDT resistance mechanism in this population. The carbamate resistance in this population is conferred by an altered acetylcholinesterase based resistance mechanism. The level of resistance observed in the bioassays correlates with the frequency of individuals homozygous for the altered AChE allele. This suggests that the level of resistance conferred by this mechanism in its heterozygous state is below the level of detection of the bioassay. The low levels of OP and pyrethroid resistance could be conferred by either the elevated esterase or monooxygenase enzymes. The esterases however are elevated only with PNPA, and are unlikely to be causing broad spectrum OP resistance. The altered AChE mechanism may also be contributing to the OP but not the pyrethroid resistance.