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. GRAPHICAL ABSTRACT