Dose-response assay for highly volatile pyrethroids against Aedes aegypti and Anopheles minimus (Diptera:Culicidae) using a high-throughput screening system

Spatial repellents (SRs) providing ‘safe zone’ for human host both in- and out-door have studied actively to support conventional vector mosquito control strategies such as indoor residual spray (IRS) and long-lasting insecticide treated nets (LLINs) which are facing coverage gaps, especially for outdoor transmission. Recently, specific lethal discriminating concentrations (DCs) of transfluthrin (TFT) has determined using WHO tube bioassay. However, behavioral responses were not determined. In this study, two highly volatile pyrethroids: TFT and metofluthrin (MET) were explored further using 3 in 1 high-throughput screening system (HITSS): toxicity (TOX), contact irritancy (CIA) and spatial repellency assays (SRA). First, we generated DCs of each SR against permethrin-susceptible laboratory strain of Aedes aegypti (USDA) using TOX assay. Furthermore, susceptibility tests against permethrin-resistance field-collected population of Ae. aegypti (Pu-Teuy) were conducted using the final DCs determined based on doubling 99% lethal concentrations of each chemical. Subsequently, behavioral responses of both pyrethroids-susceptible and -resistance Ae. aegypti against various lethal concentrations: 50%, 75%, 99%, and DC of TFT were observed using CIA and SRA.Overall, although the DC of TFT (0.15232%) was 4.7-folds higher than MET (0.03244%), 24 h mortality of Ae. aegypti (Pu-Tuey) between TFT and MET were not significantly different (P = 0.002, 75.0% ± 12.6% and 61.7% ± 12.1%, respectively). In addition, behavioral responses against sub-lethal concentrations of TFT were clearly observed from field population of Ae. aegypti (Pu-Teuy) which showed lower knockdown rates than laboratory strain (USDA) in the HITSS device.