| Summary: | <i>Aedes aegypti</i> is a major vector of dengue fever in tropical regions. Spatial repellents (SRs) have shown promise in delaying pesticide resistance. Methods for discriminating concentrations (DCs) are well established using various bioassay tools, while data for high-throughput screening system (HITSS) toxicity bioassay (TOX) are absent. In this study, we compared and optimized lethal (LCs) and sub-lethal concentrations (SLCs) of transfluthrin (TFT) and metofluthrin (MFT) on pyrethroid-susceptible (USDA) and pyrethroid-resistant (Pu-Teuy) <i>Ae. aegypti</i> (L.) strains, using the HITSS-TOX. Mean mortality (MT) was 100% at LC<sub>99</sub> and DC, compared to LC<sub>50</sub> (45.0 ± 3.7%) and LC<sub>75</sub> (65.8 ± 7.0%) for the USDA strain. However, the resistant strain (Pu-Teuy) showed reduced susceptibility against TFT and a significantly lower MT at LC<sub>50</sub> (12.5 ± 4.4%; t = 5.665, df = 10, <i>p</i> < 0.001), LC<sub>75</sub> (9.2 ± 3.5%; t = 4.844, df = 10, <i>p</i> = 0.001), LC<sub>99</sub> (55.0 ± 9.9%; t = 4.538, df = 5, <i>p</i> = 0.006), and DC (75.0 ± 5.2%; U = 3.0, <i>p</i> = 0.007). The DC of TFT (0.15222%) was 4.7-fold higher than for MFT (0.03242%) in USDA strain. The baseline DCs established are useful to better understand susceptibility and the efficacy of various repellents against field populations of <i>Ae. aegypti</i>.
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