Susceptibility to the larvicide pyriproxyfen and genotyping of kdr mutations in two Aedes aegypti populations from Maranhão State, Brazil.

Aedes aegypti is the main vector of arboviruses in the Americas, including dengue, Zika and chikungunya. In Brazil, initial control strategies relied on insecticides, but their continuous use has promoted resistance, mainly through metabolic changes and knockdown resistance (kdr) mutations, which are key molecular markers of pyrethroid resistance. This study evaluated the susceptibility of Ae. aegypti populations from Caxias and São Mateus (Maranhão State) to the larvicide pyriproxyfen and investigated the frequency of the kdr SNPs V410L, V1016I and F1534C. Eggs collected in the field were reared to the F1 generation, and L3 larvae were subjected to quantitative bioassays to determine emergence inhibition (EI) indexes. DNA extracted from adults was analyzed by qPCR to assess kdr allele frequencies. Bioassays showed 98 % mortality in Caxias and 100 % in São Mateus when exposed to 0.8 μg/mL of pyriproxyfen. EI50 values were 0.094 mg/L and 0.083 mg/L, while EI90 values reached 1.596 mg/L and 0.558 mg/L, respectively. Resistance ratios, relative to the Rockefeller strain, were 1.175 and 1.038, indicating susceptibility. Regarding kdr markers, we observed a predominance of the kdr R1 allele (VVC, mutated at site 1534) in Caxias (50 %) and of the kdr R2 allele (LIC, mutated at sites 410, 1016 and 1534) in São Mateus (53 %). The wild-type S allele (VVF, without mutations) showed frequencies of 47 % and 8 % in Caxias and São Mateus, respectively. Despite the presence of pyrethroid-resistant alleles, no phenotypic resistance to the IGR pyriproxyfen was observed. These results confirm the effectiveness of pyriproxyfen against Ae. aegypti in Maranhão, while the presence of kdr mutations underscores the need for ongoing surveillance and integrated management to prevent resistance.