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.

Human landing catches provide a useful measure of protective efficacy for the evaluation of volatile pyrethroid spatial repellents

“…Eave-positioned targeted insecticide (EPTI) emanators comprising 4 m × 0.1 m strips of hessian treated with 5 g, 10 g, 15 g, or 20 g of transfluthrin [27] were used for the experiments with Anopheles. For Aedes mosquitoes, freestanding transfluthrin passive emanators (FTPEs) [28] comprising 5 m × 0.1 m hessian strips treated with the same four doses of transfluthrin were used. Negative controls were prepared in the same way with water.…”

“…Of these outcomes, only repellence can be appropriately evaluated by HLC, as only mosquitoes that land are taken into consideration in the analysis. Other outcomes such as mortality or knock-down may not be fully assessed by HLC [28,45], as mosquitoes will spend more time in contact with the treated device while blood-feeding, which may increase mortality. Conversely, blood-fed mosquitoes show enhanced survival when exposed to pyrethroids [52].…”

To Kill or to Repel Mosquitoes? Exploring Two Strategies for Protecting Humans and Reducing Vector-Borne Disease Risks by Using Pyrethroids as Spatial Repellents

“…This risk could theoretically be reduced if SR use is combined with push-pull strategies, notably those in which SRs (push) are paired with traps containing CO 2 or other attractants (pull) [ 59 ]. However, several studies have found that such combined approaches do not work better than the use of repellents alone [ 60 , 61 , 62 ], so further community-level research is merited.…”

Improving the efficiency of household insecticide testing against mosquitoes

“…Widespread reports of insecticide resistance indicate threats to public health anti-vector programmes (1,2). In response, at least in part, alternative insecticide-based tools for public health have been further explored, with increasing interest in pyrethroid-based ambient insecticides such as spatial repellents (3)(4)(5). Herein, ambient insecticides refer to aerosolized and volatile insecticides (spatial repellents) deployed by candles, mats, emanators, sprays and coils.…”