Barrier screens: a method to sample blood-fed and host-seeking exophilic mosquitoes

Abstract

BackgroundDetermining the proportion of blood meals on humans by outdoor-feeding and resting mosquitoes is challenging. This is largely due to the difficulty of finding an adequate and unbiased sample of resting, engorged mosquitoes to enable the identification of host blood meal sources. This is particularly difficult in the south-west Pacific countries of Indonesia, the Solomon Islands and Papua New Guinea where thick vegetation constitutes the primary resting sites for the exophilic mosquitoes that are the primary malaria and filariasis vectors.MethodsBarrier screens of shade-cloth netting attached to bamboo poles were constructed between villages and likely areas where mosquitoes might seek blood meals or rest. Flying mosquitoes, obstructed by the barrier screens, would temporarily stop and could then be captured by aspiration at hourly intervals throughout the night.ResultsIn the three countries where this method was evaluated, blood-fed females of Anopheles farauti, Anopheles bancroftii, Anopheles longirostris, Anopheles sundaicus, Anopheles vagus, Anopheles kochi, Anopheles annularis, Anopheles tessellatus, Culex vishnui, Culex quinquefasciatus and Mansonia spp were collected while resting on the barrier screens. In addition, female Anopheles punctulatus and Armigeres spp as well as male An. farauti, Cx. vishnui, Cx. quinquefasciatus and Aedes species were similarly captured.ConclusionsBuilding barrier screens as temporary resting sites in areas where mosquitoes were likely to fly was an extremely time-effective method for collecting an unbiased representative sample of engorged mosquitoes for determining the human blood index.

Entomological surveillance of behavioural resilience and resistance in residual malaria vector populations

“…Incorporate surveys of vector feeding and resting behaviours, using human landing catch by participants protected with drug chemoprophylaxis [76] and backpack aspirator/screening barrier sampling tools [84,85], respectively, into these quality assurance surveys to quantify the extent to which each important vector species feeds on humans, feeds indoors or rests indoors.…”

Characterizing, controlling and eliminating residual malaria transmission

“…Given the reliance of scalable trapping schemes, especially those which are community-based, upon widely scattered, field-based personnel who may not always perform adequately [118, 119], it is also essential to establish quality assurance systems in which each of these sentinel sites is regularly and randomly re-surveyed by a centrally coordinated, specialist entomological team using the same trapping methods [31, 120]. Given the diversity of vector species and behaviours across the tropics, setting up such platforms for monitoring mosquito population dynamics may require initial pilot evaluations to select and calibrate suitable trapping methods or validate calibrations from elsewhere.3.Incorporate surveys of vector feeding and resting behaviours (using human landing catch by participants protected with drug chemoprophylaxis [128] and backpack aspirator/resting container/screening barrier sampling tools [129–131], respectively) into the quality assurance surveys described above under point 2, so that the extent to which each important vector species feeds on humans, feeds indoors, or rests indoors, can be quantified.4.Integrate monitoring of relevant human behaviours [16] and ecology, including resource use and livelihoods, vector control coverage and livestock ownership into national malaria surveys and/or entomologic surveillance platforms, so that their contributions to intervention limitations and failures can be assessed.5Where substantial transmission occurs indoors, experimental hut [132–134] facilities should be established at one or two sentinel sites where the most nationally-relevant vector species are abundant, so that the efficacy of vector control interventions can be assessed before and after their introduction [39]. …”

Going beyond personal protection against mosquito bites to eliminate malaria transmission: population suppression of malaria vectors that exploit both human and animal blood

“…While direct experimental measurements of host preference40 provided evidence that led us to include A. dirus and A. minimus in figure 2, both species are absent from figure 1, presumably because blood-fed specimens of these outdoor-resting mosquitoes are notoriously difficult to capture. Correspondingly, the only contemporary data point for A. farauti in figure 1 arose from recent innovations in methods for sampling outdoor-resting mosquitoes 41…”