High-throughput screening method for evaluating spatial repellency and vapour toxicity to mosquitoes

Spatial repellents are an essential tool for personal protection against mosquitoes that bite and transmit disease pathogens to humans. Current repellent screening methods, such as olfactometers and alternative choice tests, are complex systems that require a relatively large quantity of compound (mg). The present study validates a high-throughput spatial repellent screening method using a glass tube that has the ends covered with netting, in addition to treated filters and plastic end caps. The apparatus occupies relatively little space, is easy to decontaminate, and requires small amounts of compound (μg). In a horizontal tube orientation, DEET (N,N-diethyl-meta-toluamide), citronella oil and IR3535 had 1 h half repellent concentration (EC₅₀ ) values of 32, 32 and 298 μg/cm² , respectively, against the Orlando strain of Aedes aegypti (L.) (Diptera: Culicidae). Vertical tube orientation increased EC₅₀ values by approximately two-fold, except IR3535, which remained essentially unchanged. Transfluthrin showed concentration-dependent spatial repellency (1 h EC₅₀  = 0.5 μg/cm² ) without any knockdown, although only in vertical tubes. Transfluthrin showed 50% knockdown in 1 h at 0.5 μg/cm² and 50% mortality at 0.15 μg/cm² in horizontal tubes. In conclusion, this high-throughput screening method is useful for assessing vapour toxicity and the spatial repellency of candidate molecules prior to semi-field and field studies.