Adapting a simplified bioassay for the evaluation of susceptibility status in Anopheles darlingi and Anopheles marajoara larvae to the pyrethroid deltamethrin

Abstract

Malaria remains one of the most serious public health problems in the world. The most effective strategic tool to reducing the transmission of the disease is the elimination of the mosquito vectors, through applying chemical insecticides against the adult form. However, the overuse of such compounds has been causing a strong selection pressure on vector populations, resulting in the emergence of resistance. In this study, we aimed to adapt a method for assessing susceptibility status to pyrethroid insecticides on larvae of Anopheles darlingi and Anopheles marajoara. This method was previously named as Knockdown Simplified Bioassay. The samples were collected in Manaus, São Gabriel da Cachoeira and Iranduba in the state of Amazonas, in Macapa, Amapa, and Rio Branco, Acre. Bioassays were performed using 4th instar larvae. Each larva was placed in cups containing 20 mL of the insecticide solution and the time of knockdown was observed for 30 minutes. Based on natural population most susceptible (São Gabriel da Cachoeira), diagnostic doses obtained were 0.1 and 0.4 ppm. Loss of susceptibility was observed in populations of Manaus and Iranduba, possibly due to selection effect of insecticides on the specific resistance alleles.