Reducing biting rates of Aedes aegypti with metofluthrin: investigations in time and space

Abstract

Background: Indoor residual spraying is key to dengue control in Cairns and other parts of northern Queensland, Australia, where Aedes aegypti is prevalent, but the strategy faces challenges with regards to slow application time and, therefore, community coverage. A faster potential improvement might be the use of polyethylene netting impregnated with the volatile pyrethroid metofluthrin (SumiOne™). This formulation was assessed in rooms in three houses in Cairns, Australia. One emanator was placed in each room and cages of 10 female Aedes aegypti were exposed at distances of 1 and 3 m. Knockdown and landings on a human hand were counted before metofluthrin exposure and at 10, 30, 60, 90 and 120 min during exposure. In addition, two trials continued over 48 h of exposure to assess the long-term sublethal effects of metofluthrin on caged mosquitoes.

Results: Percentage landing rates fell to 0-2.5% in the first 10 min of exposure. Knockdown was most evident between 10 and 30 min (54% at 1 m and 33% at 3 m). Distance from the emanator strongly affected the results: mosquitoes at 3 m exhibited less knockdown and more landings than those at 1 m. As room volume increased, knockdown decreased and the number of landing increased. There is a cumulative mortality and landing inhibition and, for mosquitoes exposed to metofluthrin for > 48 h, mortality was 100% at 1 m and 90% at 3 m. Of those still alive, a small number continued to land and bite. After being removed from metofluthrin-treated rooms, exposed insect cages were found to reducing landing rates for up to 2 h.

Conclusions: Despite only moderate levels of knockdown during the initial hours of exposure, metofluthrin emanators were effective in reducing mosquito landing rates, especially within 1 m, even when exposed on an open veranda. The evaluation methods and results described in this paper will help inform the optimal conditions of deployment of metofluthrin emanators. These devices have the potential to reduce contact between humans and urban disease vectors faster than indoor residual spraying so supplement our current arsenal of dengue control tools.

Keywords: Aedes aegypti; Dengue; Metofluthrin; Vector control; Volatile pyrethroids.

Fig. 1

One of the trial rooms. Lounge, House #2. One mosquito cage is within 1 m of the metofluthrin emanator (arrow) and the other cage is 3 m away

Fig. 2

Aedes aegypti probing on a human hand after exposure to metofluthrin emanators. Height of bars represents the mean ± SE of probing mosquitoes (n = 10 in all trials). a-b, House #1. c-d, House #2. e-f, House #3. See Table 1 for dimensions and volumes of rooms

Fig. 3

Aedes aegypti knockdown after exposure to metofluthrin emanators at two distances in three houses. Height of bars represents the mean ± SE of knocked down mosquitoes (n = 10 in all trials). Knocked down was defined as could not fly or walk after the cage was gently tapped against the floor. a-b, House #1. c-d, House #2. e-f, House #3. See Table 1 for dimensions and volumes of rooms

Fig. 4

Mean landing rates of Aedes aegypti on a human hand with metofluthrin emanators. Estimated means (± SE) based on generalized estimating equation. Values with identical lowercase letters are not significantly different based on pairwise comparisons (using Fisher’s LSD to control for multiple comparisons)

Fig. 5

Estimated means of Aedes aegypti knockdown in the presence of metofluthrin emanators. Estimated means (± SE) based on generalized estimating equation. Values with identical lowercase letters are not significantly different based on pairwise comparisons (using Fisher’s LSD to control for multiple comparisons)

Fig. 6

Mosquito probing in the presence of metofluthrin emanators over 48 h. Height of bars represent the mean ± SE of mosquitoes resting and probing on a human hand within a 2 min period (n = 10 in all trials). All trials are from House #2

Fig. 7

Mosquito probing in a cage that had been previously been exposed to a metofluthrin emanator for 2 h