Behavioral Responses of Pyrethroid-Susceptible and Pyrethroid-Resistant Aedes aegypti (Diptera: Culicidae) to Transfluthrin and Metofluthrin in High-Throughput Screening System Assays

Abstract

Dengue and other arboviruses remain major public health concerns, with Aedes aegypti as the primary vector. Pyrethroid resistance has reduced the effectiveness of conventional insecticides, prompting interest in volatile pyrethroid spatial repellents (VPSRs) such as transfluthrin (TFT) and metofluthrin (MFT). These compounds modify behavior by deterring host contact or inducing escape. Using the high-throughput screening system, evaluated behavioral responses of pyrethroid-susceptible (USDA) and pyrethroid-resistant (Pu-Teuy) Ae. aegypti to VPSRs via contact irritancy (CIA) and spatial repellency (SRA) assays, referencing baseline toxicity (TOX) data. Resistant mosquitoes exhibited significantly lower knockdown (KD) and mortality (MT) than susceptible counterparts under contact exposure (CIA KD at LC₅₀: USDA 43.3% ± 18.6% vs. Pu-Teuy 0.0% ± 0.0%; p < 0.05). Transfluthrin retained partial efficacy, eliciting contact escape responses up to 65.0% ± 17.6% in USDA (at LC₉₉) and 71.7% ± 14.7% in Pu-Teuy (at LC₇₅). At discriminating concentrations (DCs), MFT elicited stronger contact escape than TFT in resistant mosquitoes (50.0% ± 6.3% vs. 33.3% ± 15.1%) but produced lower contact toxicity (5.0% ± 5.5% vs. 55.0% ± 18.7% MT). In SRA, TFT produced stronger noncontact deterrence, yielding Spatial Activity Index values of 0.69 (USDA) and 0.51 (Pu-Teuy), compared to 0.31 (USDA) and 0.22 (Pu-Teuy) for MFT. Integration of TOX, CIA, and SRA revealed marked divergence between lethal and behavioral endpoints. Compound-specific behavioral profiles TFT as a noncontact spatial deterrent and MFT as a contact excito-irritant support their tailored deployment as the “push” component in multimodal “push-pull” vector management strategies combining spatial repellents with baited traps.