Large-scale deployment of pyriproxyfen-treated Lehmann’s Funnel Entry Traps to control malaria mosquito populations

Abstract

Abstract Background There is a great need to find new effective tools to prevent mosquitoes from biting humans. As part of this search, the Lehmann Funnel Entry Trap, a window screen, was tested and has proven to be effective in mosquito density reduction in low and high vector density settings. Here we aimed to assess whether a large-scale deployment of pyriproxyfen-treated traps can control malaria mosquito populations and how well the traps were accepted at community level. Method Overall, 1,313 traps impregnated with Pyriproxyfen (PPF) were deployed. Of these, 12 traps in 12 houses were randomly selected across the intervention village, Vallée du Kou 3 (VK3), for indoor mosquito density assessment compared to houses without traps in the control village, Vallée du Kou 5 (VK5). Traps were placed in the windows, while doors were blocked with curtains. From July until October 2015, for nine days per month, mosquitoes were collected from the traps and matching houses in VK3, and in houses only in VK5. Anopheles coluzzii collected from the field as adults and as larvae reared through to adults and An. gambiae were used or released into traps to assess the bio-efficacy effect of PPF in VK3 against control mosquitoes from VK5. Then, mosquitoes that were in contact with the PPF trap netting were allowed to oviposit in the laboratory for fecundity and egg fertility reduction evaluation as compared to a control. The mosquitoes collected as part of the monthly programme were morphologically identified, counted, and preserved in 80% ethanol vials for subsequent analyses, including resistance genes and female mosquito age structure. The impact of the trap on mosquito density at community level was assessed by performing a pyrethrum spray catch (PSC). The integrity of net fabric as well as some sociological points of view on the trap’s efficacy and design were then reported. Results Overall mosquito density was reduced by ~ 90% in all houses equipped with traps in VK3. At the community level, while mosquito density before intervention was 33% higher in VK3 than in VK5, it was 47% higher in VK5 after the intervention. Old female mosquito numbers increased in VK5 by 12% in October but not in VK3, indicating that the traps were cumulatively killing older females. The additional effect of PPF was to limit egg-laying, with a smaller number of eggs counted, and with a lower hatching rate than in VK5. Mosquitoes were highly resistant to pyrethroids with a ~ 0.9 frequency of the kdr mutation. The trap was well accepted by the communities as most of the interviewees in VK3 found the traps reduced mosquito bites with peaceful sleep. They hoped to keep the traps in place beyond the study period. Conclusion The Lehmann Funnel Entry Trap has real potential to control malaria mosquito populations and can be widely used to sustain the global effort of malaria elimination.