Measuring, manipulating and exploiting behaviours of adult mosquitoes to optimise malaria vector control impact

Abstract

Residual malaria transmission can persist despite high coverage with effective long-lasting insecticidal nets (LLINs) and/or indoor residual spraying (IRS), because many vector mosquitoes evade them by feeding on animals, feeding outdoors, resting outdoors or rapidly exiting from houses after entering them. However, many of these behaviours that render vectors resilient to control with IRS and LLINs also make them vulnerable to some emerging new alternative interventions. Furthermore, vector control measures targeting preferred behaviours of mosquitoes often force them to express previously rare alternative behaviours, which can then be targeted with these complementary new interventions. For example, deployment of LLINs against vectors that historically fed predominantly indoors on humans typically results in persisting transmission by residual populations that survive by feeding outdoors on humans and animals, where they may then be targeted with vapour-phase insecticides and veterinary insecticides, respectively. So while the ability of mosquitoes to express alternative behaviours limits the impact of LLINs and IRS, it also creates measurable and unprecedented opportunities for deploying complementary additional approaches that would otherwise be ineffective. Now that more diverse vector control methods are finally becoming available, well-established entomological field techniques for surveying adult mosquito behaviours should be fully exploited by national malaria control programmes, to rationally and adaptively map out new opportunities for their effective deployment.

Reduced human-biting preferences by the African malaria vectors Anopheles arabiensis and Anopheles gambiae in an urban context: Controlled, competitive host-preference experiments in Tanzania

“…It is also telling that a similar, and perhaps more surprising, the pattern was observed for the notoriously anthropophagic [6,27,49,50] An. gambiae when compared with a previous study of the same species in a rural Tanzanian context (Figure 3).…”

“…This newly observed behavioural plasticity, allows the mosquito to evade human-targeted insecticidal based interventions by allowing it to access safer alternative blood sources [29,30]. This behaviour may help vector species to sustain its population and contribution to residual malaria transmission by evading fatal contact with existing front-line interventions [6,31,32].…”

“…Apart from the distributions of bites between inside and outsides the houses, and at a different time of the night [1,2], what hosts mosquito prefers to feed on (host preference) critically determines the choice and impact of human-targeted vector control interventions [3][4][5][6][7][8]. For example, both historical and recent reports [9][10][11][12][13][14][15] show that the widespread use of long-lasting insecticides treated nets (LLNs) or indoor residual spraying (IRS), which are directly targeted on humans or houses they live in, strongly suppressed or even virtually eliminated the population of malaria vectors Anopheles gambiae sensu stricto and Anopheles funestus sensu stricto, which both feed predominantly upon human blood all across sub-Saharan Africa [10,11,[16][17][18].…”

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

“…Indeed a promising array of new vector control products and prototypes, such as attractive sugar baits, vapour-phase insecticide emanators, veterinary insecticides and house entry traps, are now emerging that could be horizontally delivered to end users almost anywhere in some of the poorest countries in the world 20. Furthermore, all the adult mosquito behaviours which these intervention options target can be readily quantified with existing, accessible, well-established entomological field techniques 53. Such metrics of targetable mosquito behaviours may therefore be used to rationally select, monitor and evaluate optimal intervention choices, to maximise impact on malaria transmission 53…”

Evidence of extrinsic factors dominating intrinsic blood host preferences of major African malaria vectors

“…Malaria-transmitting mosquitoes are often described as primary or secondary vectors with this categorisation informed, in part, by their level of anthropophagy as indicated by their HBI. Owing to the influences of different environmental settings, however, studies reporting HBI for the same vector species demonstrate considerable variability 21,[23][24][25] . We recently showed that the HBI of Anopheles coluzzii varied significantly over an extraordinarily small spatial scale, thus demonstrating how localised host biting behaviour can be 26 .…”