Performance of different spatial repellents (spatial emanators) against vector mosquito species in Mali, West Africa: a field trial using a non-human test method.

WEST Africa; MALI

Introduction: Spatial repellents (also called spatial emanators) are widely marketed for personal protection against mosquito bites, yet their real‑world performance varies substantially and is rarely evaluated under standardized field conditions. This study quantified the protective efficacy of six consumer‑available repellent devices at paired urban (Aedes -dominated) and rural (Anopheles -dominated) field sites in Mali, West Africa. Methods: Products included a Dynatrap® Mosquito Repellent electronic device with an 8.83% transfluthrin-containing replaceable heat-activated cartridge, a Thermacell^® E90 Rechargeable Mosquito Repeller electronic device with a 5.5% transfluthrin-containing replaceable heat-activated cartridge, two mosquito coils (Hassana containing 0.08% meperfluthrin and PIC^® containing 0.6% pyrethrins), a Cutter^® CitroGuard^® Candle containing 3% citronella oil, and an Isotronic mosquito repellent device with an oscillating frequency technology. Each product was tested in wind‑controlled V‑shaped field plots using three CO2‑baited CDC‑UV traps, positioned 14 ft from the device, to quantify spatial protection. Results: Across both sites, the heat-activated volatile pyrethroid devices achieved the strongest and most consistent reductions in mosquito captures. At the urban site, the Dynatrap^® and Thermacell devices lowered mean Aedes counts from all traps in all replicates 14.33 ± 2.05 in the control to 0.96 ± 0.27 and 0.88 ± 0.26, respectively, and reduced mean Culex counts from 8.83 ± 1.40 to 0.50 ± 0.21 and 1.00 ± 0.29, respectively. At the rural site, where Anopheles were predominant, these same devices decreased mean captures from 34.96 ± 7.20 in the control to 1.63 ± 0.49 (Dynatrap^®) and 2.50 ± 0.63 (Thermacell^®). Culex were reduced from 15.79 ± 2.91 to 2.63 ± 0.61 (Dynatrap^®) and 4.00 ±0.69 (Thermacell^®) at the same site. Dunnett's multiple comparisons confirmed that these were the only treatments to produce significant reductions across multiple genera at both sites. Mosquito coils offered moderate but inconsistent protection, while the citronella candle and ultrasonic device showed minimal or no measurable effect, aligning with previous findings that citronella‑based products provide little field efficacy. This characterization of "inconsistent" reflects the night‑to‑night fluctuations in percent reduction, which are evident in the raw data (not shown) and already conveyed in the reported means and confidence intervals. Discussion: Together, these results demonstrate that heat‑activated volatile pyrethroid devices can deliver strong, broad‑spectrum spatial protection across ecologically varied environments. The study emphasizes the need for standardized, wind‑controlled field testing and highlights significant performance gaps among widely marketed consumer repellents. Given that spatial repellents are now formally recognized as a recommended intervention class in the 2025 WHO Guidelines, these performance gaps carry important public health implications, as inconsistent or underperforming products could undermine the protective value expected from this intervention category. [ABSTRACT FROM AUTHOR]

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