Resistance surveillance in Aedes aegypti using bottle bioassays and molecular KDR screening

Insecticide resistance is a major problem and can occur when pesticides are misused, overused, or not properly rotated. For vector control of medically important insects, such as mosquitos, resistance surveillance is critical. Bottle bioassays test expressed resistance by assessing time-based mortality for a group of mosquitos in a jar covered in residual insecticide. One measure of potential resistance is to screen for genetic mutations in the voltage-gated sodium channel which confers knock down resistance (KDR) which decrease the effectiveness of pyrethroid insecticides through target-site insensitivity. We determined the pyrethroid resistance levels in Aedes aegypti populations from across the city of New Orleans, Louisiana, using both bottle bioassays and genetic KDR screening. Bottle bioassays were conducted with mosquito populations from 36 locations in the city with five different pyrethroids and two organophosphates. We screened for two KDR mutations (V1016I, F1534C) using real-time PCR in each individual mosquito to determine the correlation of KDR mutations and survival in the bottle bioassay. In our bottle bioassays, we found more resistance to pyrethroids than organophosphates, but generally most populations were susceptible to both pesticide types. Our KDR results were similar and ~95% of individuals carried neither allele and 1% of individuals were homozygous for both alleles. There was a positive correlation between the number of alleles an individual carried and the percent survival in the bottle bioassays (P = 0.02, r² = 0.63). This indicates that the bottle bioassays and KDR analysis provide approximately the same assessment of resistance in Ae. aegypti mosquitos.