Evaluating Putative Repellent ‘Push’ and Attractive ‘Pull’ Components for Manipulating the Odour-orientation of Host-seeking Malaria Vectors in the Peri-domestic Space
Abstract Background Novel malaria vector control approaches aim to combine tools to work in synergy for maximum protection. This study aimed to evaluate novel and re-evaluate existing, putative repellent ‘push’ and attractive ‘pull’ components for manipulating the odour-orientation of malaria vectors in the peri-domestic space. Methods Anopheles arabiensis outdoor human landing catches and trap comparisons were implemented in large semi-field systems to (1) test the efficacy of citriodiol or transfluthrin-treated fabric strips positioned in house eave gaps as push components for preventing bites; (2) understand the efficacy of an MB5-baited Suna-trap in attracting vectors in the presence of a human being; (3) assess 2-butanone as a CO2 replacement for trapping; and (4) determine the protection provided by a full push-pull set up. The air-concentrations of the chemical constituents of the push-pull mosquito control tool were quantified.Results Microencapsulated citriodiol eave strips did not provide any outdoor protection against host-seeking An. arabiensis. Transfluthrin-treated strips significantly reduced the odds of a mosquito landing on the human volunteer (OR 0.17; 95% CI 0.12-0.23). This impact was lower (OR 0.59; 95% CI 0.52-0.66) during the push-pull experiment which was associated with low night-time temperatures likely affecting the transfluthrin vaporisation. The MB5-baited Suna trap supplemented with CO2 attracted only a third of the released mosquitoes in the absence of a human being, however, with a human volunteer in the same system, the trap caught less than 1% of all released mosquitoes. The volunteer consistently attracted over two-thirds of all mosquitoes released. This was the case in the absence (‘pull’ only) and in the presence of a spatial repellent (‘push-pull’), indicating that in its current configuration the tested ‘pull’ does not provide a valuable addition to a spatial repellent. The chemical 2-butanone was ineffective in replacing CO2. Transfluthrin was detectable in the air space but with a strong linear reduction in concentrations over 5 metres from release. The MB5 constituent chemicals were only irregularly detected, potentially suggesting insufficient release and concentration in the air for attraction.Conclusion This step-by-step evaluation of the selected ‘push’ and ‘pull’ components led to a better understanding of their ability to affect host-seeking behaviours of the malaria vector Anopheles arabiensis in the peri-domestic space and helps to gauge the impact such tools would have when used in the field for monitoring or control.