Evaluation of a push–pull system consisting of transfluthrin-treated eave ribbons and odour-baited traps for control of indoor- and outdoor-biting malaria vectors

Abstract

BackgroundPush–pull strategies have been proposed as options to complement primary malaria prevention tools, indoor residual spraying (IRS) and long-lasting insecticide-treated nets (LLINs), by targeting particularly early-night biting and outdoor-biting mosquitoes. This study evaluated different configurations of a push–pull system consisting of spatial repellents [transfluthrin-treated eave ribbons (0.25 g/m2 ai)] and odour-baited traps (CO2-baited BG-Malaria traps), against indoor-biting and outdoor-biting malaria vectors inside large semi-field systems.MethodsTwo experimental huts were used to evaluate protective efficacy of the spatial repellents (push-only), traps (pull-only) or their combinations (push–pull), relative to controls. Adult volunteers sat outdoors (1830 h–2200 h) catching mosquitoes attempting to bite them (outdoor-biting risk), and then went indoors (2200 h–0630 h) to sleep under bed nets beside which CDC-light traps caught host-seeking mosquitoes (indoor-biting risk). Number of traps and their distance from huts were varied to optimize protection, and 500 laboratory-reared Anopheles arabiensis released nightly inside the semi-field chambers over 122 experimentation nights.ResultsPush-pull offered higher protection than traps alone against indoor-biting (83.4% vs. 35.0%) and outdoor-biting (79% vs. 31%), but its advantage over repellents alone was non-existent against indoor-biting (83.4% vs. 81%) and modest for outdoor-biting (79% vs. 63%). Using two traps (1 per hut) offered higher protection than either one trap (0.5 per hut) or four traps (2 per hut). Compared to original distance (5 m from huts), efficacy of push–pull against indoor-biting peaked when traps were 15 m away, while efficacy against outdoor-biting peaked when traps were 30 m away.ConclusionThe best configuration of push–pull comprised transfluthrin-treated eave ribbons plus two traps, each at least 15 m from huts. Efficacy of push–pull was mainly due to the spatial repellent component. Adding odour-baited traps slightly improved personal protection indoors, but excessive trap densities increased exposure near users outdoors. Given the marginal efficacy gains over spatial repellents alone and complexity of push–pull, it may be prudent to promote just spatial repellents alongside existing interventions, e.g. LLINs or non-pyrethroid IRS. However, since both transfluthrin and traps also kill mosquitoes, and because transfluthrin can inhibit blood-feeding, field studies should be done to assess potential community-level benefits that push–pull or its components may offer to users and non-users.

Evaluating Putative Repellent ‘Push’ and Attractive ‘Pull’ Components for Manipulating the Odour-orientation of Host-seeking Malaria Vectors in the Peri-domestic Space

“…Trans uthrin has been incorporated into commercial products for mosquito control with encouraging outcomes (27,40,(90)(91)(92)(93)(94). Applied on hessian material for passive emanation, it has been proposed to protect from 70-90% of bites from Afrotropical malaria vectors in a range of experimental laboratory and eld studies implemented in coastal and inland Tanzania (21,49,89,95,96). Our results con rm the potential of trans uthrin for use as a spatial repellent vector control tool.…”

Use of semiochemicals for surveillance and control of hematophagous insects

“…The most commonly used slow-release dispensers for behavioral manipulation of insect pests and vectors include solid matrices like polyethylene sachets, vials, beads, tubes and sticks, glass, rubber septa, rubber wicks, membranes, spiral polymer dispensers, polyvinyl chloride (PVC), gel-like dispenser matrix, wax formulation, polyamide nylon, cotton, polyester, cellulose and polyacrylate material (Heuskin et al 2011;Mweresa et al 2014a;Mmbando et al 2019). In such cases, the actual amount of semiochemicals released in the atmosphere and active range is dependent on the choice of delivery matrices, changes in environmental parameters like atmospheric pressure, temperature, wind speed, relative humidity and the physical properties of the surroundings (Torr et al 1997;Heuskin et al 2011;Baroffio et al 2016).…”

“…Repellents and attractants can also be integrated in a push-pull strategy to direct movement and manage hematophagous dipterans like tsetse flies, mosquitoes and sand flies (Vale and Torr 2004;Menger et al 2016;Mmbando et al 2019). The target insect is repelled or pushed away from a protected resource and lured or pulled to an alternative source for removal.…”

“…Recent knowledge on insect olfactory system, behavior and genomics have also enhanced the potential of applying odor-baited technologies and approaches to control mosquito vectors. However, this is limited to small scale field trials (Mmbando et al 2019;Nyasembe et al 2019). Mass deployment of odor-baited traps to reduce malaria mosquitoes and malaria prevalence in western Kenya is a spectacular proof of concept regarding the effective integration of semiochemicals for trapping of host-seeking mosquito vectors (Homan et al 2016) (Fig.…”

“…This because orientation and movement toward odor sources are also determined by the semiochemical identity and structure of the plume (Namiki and Kanzaki 2016;Liberzon et al 2018). Such knowledge has enhanced our understanding on how hematophagous insects navigate towards semiochemical sources, optimal height and distances over which odor-baited tools may be effectively attractive or repellent to target insect species in the field (Homan et al 2016;Menger et al 2016;Mmbando et al 2019). Recent studies have demonstrated flight dynamics of malaria mosquitoes around human dwellings, odor-baited traps, capture and escape dynamics (Spitzen et al 2013;Cribellier et al 2018).…”