Semi-field studies to better understand the impact of eave tubes on mosquito mortality and behaviour

Abstract

BackgroundEave tubes are a type of housing modification that provide a novel way of delivering insecticides to mosquitoes as they attempt to enter the house. The current study reports on a series of semi-field studies aimed at improving the understanding of how eave tubes might impact mosquito mortality and behaviour.MethodsExperiments were conducted using West African style experimental huts at a field site in M’be, Côte d’Ivoire. Huts were modified in various ways to determine: (i) whether mosquitoes in this field setting naturally recruit to eave tubes; (ii) whether eave tubes can reduce house entry even in the absence of screening; (iii) whether mosquitoes suffer mortality if they attempt to exit a house via treated eave tubes; and, (iv) whether screening and eave tubes might deflect mosquitoes into neighbouring houses without the intervention.ResultsNinety percent more mosquitoes (Anopheles gambiae sensu lato, and other species) entered huts through open eaves tubes compared to window slits. The addition of insecticide-treated eave tubes reduced mosquito entry by 60%, even when windows remained open. Those mosquitoes that managed to enter the huts exhibited a 64% reduction in blood feeding and a tendency for increased mortality, suggesting contact with insecticide-treated inserts prior to hut entry. When An. gambiae mosquitoes were deliberately introduced into huts with treated eave tubes, there was evidence of six times increase in overnight mortality, suggesting mosquitoes can contact treated eave tube inserts when trying to exit the hut. There was no evidence for deflection of mosquitoes from huts with screening, or screening plus eave tubes, to adjacent unmodified huts.ConclusionsEave tubes are a potentially effective way to target Anopheles mosquitoes with insecticides. That treated eave tubes can reduce mosquito entry even when windows are open is a potentially important result as it suggests that eave tubes might not need to be combined with household screening to have an impact on malaria transmission. The absence of deflection is also a potentially important result as coverage of eave tubes and/or screening is unlikely to be 100% and it is important that households that do not have the technology are not disadvantaged by those that do.Electronic supplementary materialThe online version of this article (10.1186/s12936-018-2457-4) contains supplementary material, which is available to authorized users.

Semi-field evaluation of the cumulative effects of a “Lethal House Lure” on malaria mosquito mortality

“…To conduct release–recapture studies, a screen house was erected to enclose two West African style experimental huts (Fig. 1) [18], at the experimental field site of M’be (5.209963 W and 7. 970241 N) [18, 24, 25].…”

“…1) [18], at the experimental field site of M’be (5.209963 W and 7. 970241 N) [18, 24, 25]. EaveTubes were installed in the experimental huts [20, 21] by drilling 12–15-cm holes at eave level.…”

“…The holes were drilled at a 10° angle from the horizontal, pointing slightly upwards in the huts (Fig. 1) [18].

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“…The study used Anopheles gambiae sensu lato (s.l.) mosquitoes derived from larval collections around M’be and Bouake in central Côte d’Ivoire [18]. These local populations are known to be highly resistant to pyrethroids [23, 27, 28].…”

“…In parallel with this CRT, small-scale studies are being conducted in Côte d’Ivoire to help better understand the functioning of EaveTubes, what the limitations are, and how the technology might be improved. Two recent studies [18, 19] have used field enclosures built around standard West African experimental huts [20, 21] to conduct release–recapture experiments to explore the impact of EaveTubes on overnight mortality of cohorts of mosquitoes. Both studies suggested that about 50% of mosquitoes that enter insecticide-treated tubes (in these cases, a wettable powder formulation of 10% beta-cyfluthrin) might die overnight, which is broadly in line with similar studies conducted in Kenya and Tanzania [15, 16].…”