General visual and contingent thermal cues interact to elicit attraction in female Aedes aegypti mosquitoes

Abstract

Female Aedes aegypti mosquitoes use multiple sensory modalities to hunt human hosts to obtain a blood-meal for egg production. Attractive cues include carbon dioxide (CO 2 ), a major component of exhaled breath [1,2]; heat elevated above ambient temperature, signifying warm-blooded skin [3,4]; and dark visual contrast [5,6], proposed to bridge long-range olfactory and short-range thermal cues [7]. Any of these sensory cues in isolation is an incomplete signal of a human host, and so a mosquito must integrate multi-modal sensory information before committing to approaching and biting a person [8]. Here, we study the interaction of visual cues, heat, and CO 2 to investigate the contributions of human-associated stimuli to host-seeking decisions. We show that tethered flying mosquitoes strongly orient toward dark visual contrast regardless of CO 2 stimulation and internal host-seeking status. This suggests that attraction to visual contrast is general, and not contingent on other host cues. In free-flight experiments with CO 2 , adding a dark contrasting visual cue to a warmed surface enhanced host-seeking. Moderate warmth became more attractive to mosquitoes, and mosquitoes aggregated on the cue at all non-noxious temperatures. Gr3 mutants, unable to detect CO 2 , were lured to the visual cue at ambient temperatures, but fled and did not return when the surface was warmed to host-like temperatures. This suggests that attraction to thermal cues is contingent on the presence of the additional human sensory cue CO 2 . Our results illustrate that mosquitoes integrate general attractive visual stimuli with the context-dependent thermal stimuli to seek promising sites for blood-feeding.

The thermal sense of blood-sucking insects: why physics matters

“…Some studies conducted on mosquitoes suggest that heat would not be effective by itself as a unimodal cue but modulating the response of these insects to chemical or visual cues (i.e. multimodal integration) [10][11][12]27]. The most usual interpretation of this being that heat would only act as a short-range cue, guiding the final approach.…”

“…Recently, significant effort has been invested on two aspects: the identification of the molecular bases of thermoreception [3,7] and on the way thermal information is combined with other cues [10][11][12]. I will review below some principles on how haematophagous acquire thermal information, as well as the way thermal information can be used for locating potential hosts, trying to identify relevant gaps in our knowledge.…”