Semi-field evaluation of freestanding transfluthrin passive emanators and the BG sentinel trap as a "push-pull control strategy" against Aedes aegypti mosquitoes

Abstract

Background: Spatial repellents that drive mosquitoes away from treated areas, and odour-baited traps, that attract and kill mosquitoes, can be combined and work synergistically in a push-pull system. Push-pull systems have been shown to reduce house entry and outdoor biting rates of malaria vectors and so have the potential to control other outdoor biting mosquitoes such as Aedes aegypti that transmit arboviral diseases. In this study, semi-field experiments were conducted to evaluate whether a push-pull system could be used to reduce bites from Aedes mosquitoes.

Methods: The push and pull under investigation consisted of two freestanding transfluthrin passive emanators (FTPE) and a BG sentinel trap (BGS) respectively. The FTPE contained hessian strips treated with 5.25 g of transfluthrin active ingredient. The efficacies of FTPE and BGS alone and in combination were evaluated by human landing catch in a large semi-field system in Tanzania. We also investigated the protection of FTPE over six months. The data were analyzed using generalized linear mixed models with binomial distribution.

Results: Two FTPE had a protective efficacy (PE) of 61.2% (95% confidence interval (CI): 52.2-69.9%) against the human landing of Ae. aegypti. The BGS did not significantly reduce mosquito landings; the PE was 2.1% (95% CI: -2.9-7.2%). The push-pull provided a PE of 64.5% (95% CI: 59.1-69.9%). However, there was no significant difference in the PE between the push-pull and the two FTPE against Ae. aegypti (P = 0.30). The FTPE offered significant protection against Ae. aegypti at month three, with a PE of 46.4% (95% CI: 41.1-51.8%), but not at six months with a PE of 2.2% (95% CI: -9.0-14.0%).

Conclusions: The PE of the FTPE and the full push-pull are similar, indicative that bite prevention is primarily due to the activity of the FTPE. While these results are encouraging for the FTPE, further work is needed for a push-pull system to be recommended for Ae. aegypti control. The three-month protection against Ae. aegypti bites suggests that FTPE would be a useful additional control tool during dengue outbreaks, that does not require regular user compliance.

Keywords: Aedes aegypti; BG-sentinel trap; FTPE; Odor-baited trap; Push-pull; Spatial repellent; Transfluthrin.

Fig. 1

Preparation of the freestanding emanator (FTPE) “push”. a Design of the freestanding emanator. The device measures 50 cm in height and 40 cm in diameter. It consists of three parts; the top cover, the central square pipe and a base. The central pipe rests on the base that supports the device. The pipe is divided into four portions 10 cm apart where small branches of an aluminium flat bar 15 cm long are attached. b, c Transfluthrin impregnation and drying of the hessian strips under the shade. d The FTPE (the hessian strip enclosed with the wire mesh). e The transfluthrin-treated hessian strips placed under the shade between the experiment for “field aging” for the duration of efficacy experiment

Fig. 2

Schematic representation for the experiment in the SFS. a The arrangement of push intervention. b The BGS positioned 10 m away from the human volunteer during the pull alone evaluation. c The positions of interventions during the push-pull evaluation. In each setup, a human volunteer preforming HLC sat 2 m away from the experimental hut and if push was involved, two FTPE were positioned 3 m on each side of the HLC volunteer. Small boxes at the corner represent the releasing cages positioned where mosquitoes were released

Fig. 3

Percentage of recaptured mosquitoes and protective efficacy. The arithmetic mean percentage of mosquitoes recaptured by HLC in the presence of the BGS (pull), FTPE (push), spatial repellent emanator and odour-baited trap (push-pull) compared to the control. The secondary axis shows the % protective efficacy of each intervention. Error bars represent the 95% confidence intervals

Fig. 4

The duration of efficacy of the FTPE. The arithmetic mean percentage of mosquitoes recaptured by HLC in the compartment with FTPE compared to the control up to six months after treatment. The secondary axis represents the % protective efficacy of the push at each time point. Error bars represent the 95% confidence intervals