Field Efficacy of Metofluthrin — A New Mosquito Repellent
This 2005 conference paper reported outdoor field trials of metofluthrin, a vapor-active pyrethroid, using treated paper emanators in Florida and Washington State. Each emanator contained 200 mg of metofluthrin, and protected volunteers were positioned between pairs of devices while mosquito landings were counted.The trials recorded substantial reductions in mosquito landings in both locations. The study is an early field record of passive metofluthrin emanators tested against naturally occurring mosquito populations under outdoor conditions.
What the study did and found
The researchers evaluated the repellent activity of paper substrates treated with metofluthrin under outdoor field conditions in Florida and Washington State. Each folded paper emanator had a total surface area of 4000 cm² when both sides were included and carried 200 mg of metofluthrin. To examine duration of protection, treated emanators were pre-aged for 36 hours in a wind tunnel.
Five volunteers were used in each trial. Volunteers wore Tyvek® suits and head nets to prevent biting and were positioned between two paper emanators suspended 8 feet apart. Pre- and post-treatment mosquito landing counts were made at 2-minute intervals for a maximum of 30 minutes.
In Washington, where Aedes vexans was dominant, the average pre-treatment rate was 26 mosquito landings per minute. Landing reductions exceeded 95% in all but three tests, and those three still exceeded 85%. In Florida, where mosquito density was higher and mostly Ochlerotatus spp. were reported, the average pre-treatment rate was 32 landings per minute. Seven treatments did not exceed 95% reduction, but the overall mean reductions in those treatments were greater than 80%.
Why it is cited
The paper provides an early field evaluation of a passive metofluthrin delivery system rather than relying only on laboratory observations. Its experimental design links room-temperature evaporation from treated paper with a practical field endpoint: the reduction of mosquito landings around protected volunteers.
It is also useful because the same general emanator arrangement was tested in two U.S. locations with different mosquito conditions. The Washington and Florida results show strong repellent activity while also documenting variation among individual tests rather than presenting efficacy as a single fixed percentage.
The results demonstrate substantial repellent activity while also showing that efficacy varied among individual field tests. The authors concluded that metofluthrin-treated emanators were effective at repelling mosquitoes under the outdoor conditions tested.
The 2005 trials evaluated a specific paper-emanator design containing 200 mg of metofluthrin per device. Five volunteers participated in each trial, with two emanators positioned 8 feet apart and mosquito landings recorded for periods of up to 30 minutes. Complete numerical results for every individual test were not reported, limiting additional analysis of variation between observations. The experiment measured reductions in mosquito landings rather than mosquito population control or prevention of mosquito-borne disease. The reported efficacy therefore applies to the tested device configuration and field conditions. The 36-hour pre-aging period was an experimental condition and does not establish a universal effective lifetime for other metofluthrin products. |
The topic today
Research on metofluthrin has expanded beyond the early paper-emanator experiments to include different passive delivery systems, deployment settings and mosquito species. These studies have continued to examine spatial repellency as a method of reducing human contact with mosquitoes without applying the active ingredient directly to the skin.
The 2005 field trials provided an early demonstration of this approach under outdoor conditions. In both Florida and Washington State, treated paper emanators substantially reduced mosquito landings, although the magnitude of the reduction varied among individual tests.
The experiment also demonstrated that repellent activity remained after the paper emanators had been pre-aged for 36 hours. Together, the two field locations showed that passive metofluthrin release could produce substantial reductions in mosquito landings under different mosquito pressures and species compositions.