Evaluating Transfluthrin Dose-Response Against Mosquitoes

A fully balanced cross-over dose–response experiment was conducted using two I-LACT chambers of the SFS, one for the treatment and one for the control, whereby mosquitoes could interact with the human volunteers (Fig. 2). As previous experiments did not show any difference in the numbers of mosquitoes collected between the chambers, the treated and untreated emanators were fixed to the respective chambers for the duration of the experiment to avoid any potential contamination. Each experimental day, one replicate for biting and one for landing was conducted with the same volunteers. A replicate comprised 1 h of exposure to either the treatment (transfluthrin) or the negative control. To simulate an outdoor peridomestic setting, biting or landing was conducted 2 m from the end inside the I-LACT (Fig. 3). Four doses of transfluthrin-treated emanators (5 g, 10 g, 15 g and 20 g) were evaluated consecutively. Each dose was tested for six replicates, after which the emanator with the next highest concentration of transfluthrin was used.Fig. 2

Flow chart showing the various iterations of the experiments conducted in this study

Fig. 3

Schematic representation of the I-LACT used for the experiments. a Setup of the experiment with transfluthrin-impregnated eave-positioned targeted insecticide (EPTI) strips against Anopheles mosquitoes. b Setup of the experiment with freestanding transfluthrin passive emanators (FTPE) against Aedes aegypti

Two male volunteers aged 25–40 years were recruited by written informed consent. The volunteers were non-smokers and non-alcohol drinkers, and did not use perfumed cosmetics prior to the experiment to minimize heterogeneity in their attraction to mosquitoes [29 (link)]. To standardize the area available to the mosquitoes for biting (knees and ankles), the volunteers wore closed shoes and a bug jacket (Fig. 3). The volunteers were rotated between compartments (treatments) after each experimental day (one day for landing and the following day for biting) to account for differential attractiveness to mosquitoes between individuals [30 (link)]. Temperature and humidity were recorded inside one of the I-LACT using a Tiny Tag Gemini Data Logger (Chichester, West Sussex, UK). To ensure transfluthrin vaporization, the experiments were conducted at temperatures above 23 ºC [31 (link)].
On each experimental day, the treatment and control were allocated to one of the two chambers of the I-LACT 45 min before the experiment commenced, to allow emanation of the transfluthrin to have started before the experiment began. The experiment started when the volunteer sat down on the chair and the mosquitoes were released into the chamber of the I-LACT from the release cages, which were opened by pulling a string (Fig. 3).