Abstract
Mosquito surveillance and control are at the heart of efforts to eliminate malaria, however, there remain significant gaps in our understanding of mosquito behaviour that impede innovation. We hypothesised that a combination of human-associated stimuli could be used to attract and kill malaria vectors more successfully than individual stimuli, and at least as well as a real human. To test this in the field, we quantified Anopheles responses to olfactory, visual and thermal stimuli in Burkina Faso using a simple adhesive trap. Traps baited with human odour plus high contrast visual stimuli caught more Anopheles than traps with odour alone, showing that despite their nocturnal habit, malaria vectors make use of visual cues in host-seeking. The best performing traps, however, combined odour and visual stimuli with a thermal signature in the range equivalent to human body temperature. When tested against a human landing catch during peak mosquito abundance, this “host decoy” trap caught nearly ten times the number of Anopheles mosquitoes caught by a human collector. Exploiting the behavioural responses of mosquitoes to the entire suite of host stimuli promises to revolutionise vector surveillance and provide new paradigms in disease control.
Highlights
Malaria vector control through long-lasting insecticide-treated bed nets (LLINs) and indoor residual spraying (IRS) has reduced malaria case incidence by 41% in the last 15 years[1]
Sixty malaria-endemic countries report insecticide resistance in at least one primary vector species[1] and behavioural changes following the introduction of indoor control methods appear to be increasing the proportion of biting that occurs outdoors and before people go to sleep under their bed nets[7,8,9] indoor control measures do not affect other important malaria vectors that bite and shelter predominantly outdoors[10,11]
Our aims were to (i) establish whether laboratory-observed synergies between visual, thermal and olfactory stimuli occur in outdoor-biting populations of An. gambiae complex mosquitoes, (ii) determine if high-contrast visual and thermal stimuli, simulating a warm human body, can increase the catch of host-seeking mosquitoes when combined with olfactory stimuli, and (iii) evaluate whether a host “decoy trap”, incorporating these three stimuli in imitation of a host, could intercept wild mosquitoes outdoors at least as well as a real human bait
Summary
Malaria vector control through long-lasting insecticide-treated bed nets (LLINs) and indoor residual spraying (IRS) has reduced malaria case incidence by 41% in the last 15 years[1]. The incredible success of these technologically simple interventions is based upon our knowledge of the primary African malaria vectors’ indoor feeding and resting behaviours Beyond these indoor-based interventions, only a limited range of quantified mosquito behaviours are exploited in mosquito surveillance and control methods. Recent laboratory studies have shown that both visual[4] and thermal[5] stimuli enhance close-range orientation and landing by Anopheles gambiae complex mosquitoes when these are combined with olfactory stimuli from a human. Exploitation of these non-chemical stimuli in vector monitoring and control has been neglected, impeding our ability to develop new evidence-based means of sampling and killing host-seeking mosquitoes. Our aims were to (i) establish whether laboratory-observed synergies between visual, thermal and olfactory stimuli occur in outdoor-biting populations of An. gambiae complex mosquitoes, (ii) determine if high-contrast visual and thermal stimuli, simulating a warm human body, can increase the catch of host-seeking mosquitoes when combined with olfactory stimuli, and (iii) evaluate whether a host “decoy trap”, incorporating these three stimuli in imitation of a host, could intercept wild mosquitoes outdoors at least as well as a real human bait
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