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 and obtain a blood meal for egg production. Attractive cues include carbon dioxide (CO₂), 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 multimodal sensory information before committing to approaching and biting a person [8]. Here, we study the interaction of visual cues, heat, and CO₂ 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 CO₂ 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 CO₂, adding a dark contrasting visual cue to a warmed surface enhanced attraction. Moderate warmth became more attractive to mosquitoes, and mosquitoes aggregated on the cue at all non-noxious temperatures. Gr3 mutants, unable to detect CO₂, 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 sensory cue CO₂. Our results illustrate that mosquitoes integrate general attractive visual stimuli with context-dependent thermal stimuli to seek promising sites for blood feeding.

Keywords: Aedes aegypti; behavior; behavioral contingency; carbon dioxide; host seeking; mosquito; multimodal integration; object vision; thermotaxis; visual contrast.