Screening and field performance of powder-formulated insecticides on eave tube inserts against pyrethroid resistant Anopheles gambiae s.l.: an investigation into ‘actives’ prior to a randomized controlled trial in Côte d’Ivoire

Abstract

BackgroundThe widespread emergence of insecticide resistance in African malaria vectors remains one of the main challenges facing control programmes. Electrostatic coating that uses polarity to bind insecticide particles is a new way of delivering insecticides to mosquitoes. Although previous tests demonstrated the resistance breaking potential of this application method, studies screening and investigating the residual efficacy of a broader range of insecticides are necessary.MethodsEleven insecticide powder formulations belonging to six insecticide classes (pyrethroid, carbamate, organophosphate, neonicotinoid, entomopathogenic fungus and boric acid) were initially screened for residual activity over 4 weeks against pyrethroid resistant Anopheles gambiae sensu lato (s.l.) from the M’bé valley, central Côte d’Ivoire. Tests were performed using the eave tube assay that simulates the behavioural interaction between mosquitoes and insecticide-treated inserts. With the best performing insecticide, persistence was monitored over 12 months and the actual contact time lethal to mosquitoes was explored, using a range of transient exposure time (5 s, 30 s, 1 min up to 2 min) in the tube assays in laboratory. The mortality data were calibrated against overnight release-recapture data from enclosure around experimental huts incorporating treated inserts at the M’bé site. The natural recruitment rate of mosquitoes to the tube without insecticide treatment was assessed using fluorescent dust particles.ResultsAlthough most insecticides assayed during the initial screening induced significant mortality (45–100%) of pyrethroid resistant An. gambiae during the first 2 weeks, only 10% beta-cyfluthrin retained high residual efficacy, killing 100% of An. gambiae during the first month and > 80% over 8 subsequent months. Transient exposure for 5 s of mosquitoes to 10% beta-cyfluthrin produced 56% mortality, with an increase to 98% when contact time was extended to 2 min (P = 0.001). In the experimental hut enclosures, mortality of An. gambiae with 10% beta-cyfluthrin treated inserts was 55% compared to similar rate (44%) of mosquitoes that contacted the inserts treated with fluorescent dusts. This suggests that all host-seeking female mosquitoes that contacted beta-cyfluthrin treated inserts during host-seeking were killed.ConclusionThe eave tube technology is a novel malaria control approach which combines house proofing and targeted control of anopheline mosquitoes using insecticide treated inserts. Beta-cyfluthrin showed great promise for providing prolonged control of pyrethroid resistant An. gambiae and has potential to be deployed year-round in areas where malaria parasites are transmitted by highly pyrethroid resistant An. gambiae across sub-Saharan Africa.

Fine scale spatial investigation of multiple insecticide resistance and underlying target-site and metabolic mechanisms in Anopheles gambiae in central Côte d’Ivoire

“…The insecticide selected for use in the lethal house lure CRT is the pyrethroid beta-cyfluthrin 46 . This is because a previous study showed that the EaveTubes technology delivers an overwhelming dose of insecticide causing high levels of mortality of even resistant mosquitoes 46 .…”

“…The insecticide selected for use in the lethal house lure CRT is the pyrethroid beta-cyfluthrin 46 . This is because a previous study showed that the EaveTubes technology delivers an overwhelming dose of insecticide causing high levels of mortality of even resistant mosquitoes 46 . The data from the current study provides baseline information to track whether this additional use of pyrethroids on top of LLINs in the trial area will lead to changes in phenotypic resistance and associated molecular mechanisms.…”

“…mosquitoes emerged from larvae collected in eight selected CRT villages. The pyrethroid insecticide, beta-cyfluthrin is the active deployed in the EaveTubes 46 whereas deltamethrin is the insecticide in the LLIN (PermaNet 2.0). Bioassays were conducted using papers treated with diagnostic concentration of these two insecticides: 0.05% deltamethrin and 0.15% cyfluthrin.…”

Indoor and outdoor biting behaviour of malaria vectors and the potential risk factors that enhance malaria in southern Malawi

“…For instance, house improvement protects all individuals in a house equally. This is being assessed in a number of regions (Killeen et al 2017b, McCann et al 2017b as well as the use of insecticide-impregnated tubes along the eaves, which are the preferred entry points for mosquitoes (Knols et al 2016, Sternberg et al 2016, Oumbouke et al 2018. The development of protective measures that divert malaria vectors from human beings to alternative hosts like cattle is important, especially for species with an opportunistic host-feeding behaviour such as An.…”

“…funestus which is responsible for the indoor biting in southern Malawi (Chapter 3). In other regions, structural house improvement that includes the use of tubes impregnated with insecticides along the eaves has been associated with a reduction in house entry by mosquitoes (Sternberg et al 2016, Oumbouke et al 2018.…”