Spatial repellents are commonly used terms for the volatile pyrethroids. Here we descrive semi-field experiments where the mode of action of transfluthrin beyond reducing mosquito landings is explored. Experiments were condented in a simulated peri domestic space in a semifield system using three Afrotropical malaria vectors. Transfluthrin was applied from eave positioned targeted insecticide spray (EPTIS) at 5, 10, 15 and 20g. Endpoints measured were 1) host availability measured by mosquito landings, 2) feeding success measured by proportion blood fed, 3) disarming i.e. sublethal incapacitation for one feeding cycle measured from post exposure blood feeding inhibition and knockdown 4) mortality after 24 hours and 5) reduction in eggs laid. The agreement between human landing catch and mosquito biting was measured. Transfluthrin reducted biting, and induced disarming and mortality in a dose dependent way with maximal mortality at the highest doses. The effects were similar for all three species. Human landing catch gave a slightly lower estimate of protective efficacy than if mosquitoes were allowed to bite because transfluthrin also functions by reducing biting among landed mosquitoes. For Anopheles mosquitoes, overall, the biting method measured significantly higher PE compared to the landing method (IRR=0.87, 95% CI (confidence interval): 0.81-0.93, P=0.001). However, the two methods broadly agreed and HLC remains a suitable tool for evaluating volatile pyrethroids under field conditions. Transfluthrin EPTIS reduced feeding and fertility, and increased disarming and mortality. These effects may contribute community as well as individual level protection in the peridomestic space.
