Mosquitoes are drawn to humans by combinations of sensory signals

Have you ever been bothered by a mosquito? Lab generated mutant yellow fever mosquitoes were used to show that these insects are driven to find and bite humans by detecting combinations of carbon dioxide (CO2), heat, and odor that emanate from the human body.

HFSP Long-Term Fellow Conor McMeniman and colleagues
authored on Thu, 08 May 2014

Female mosquitoes love to bite – a consequence of a strong innate drive within these insects to find blood to support egg development. During this targeted search, mosquitoes such as the yellow fever mosquito Aedes aegypti are thought to detect a variety of chemical and physical cues emanating from humans including body odor, CO2, moisture, heat, and visual contrast. How are these sensory cues detected and integrated by the mosquito nervous system to produce host-seeking and blood-feeding behavior? As a first step towards understanding how mosquitoes perceive humans, we recently used genome editing to mutate the AaegGr3 gene, a subunit of the heteromeric CO2 receptor in Aedes aegypti. This allowed us to characterize the relative contribution of CO2 detection to mosquito attraction toward humans.

Figure 1: Female Aedes aegypti mosquitoes, which spread dengue and yellow fever, feed on warm blood in the presence of CO2. Mutant mosquitoes engineered to be unable to detect CO2 are not attracted to the warm feeder. This suggests that sensation of CO2 and heat are normally integrated together by the mosquito nervous system to elicit blood feeding. Photo credit Conor McMeniman.

Gr3 mutants are blind to CO2, lacking both electrophysiological and behavioral responses to this volatile gas. Interestingly, while wild-type mosquitoes are attracted to heat or to lactic acid (a human-derived attractant) when presented in conjunction with CO2, these mutants show no response, suggesting that CO2 detection gates responses to other sensory stimuli. Despite these striking behavioral deficits in the lab, we were surprised to find that CO2 receptor mutants were only slightly impaired when challenged to find a live human in a large semi-field cage in tropical North Queensland, Australia. This hinted to us that the full complement of host cues from a live human are able compensate for the lack of CO2 detection in Gr3 mutant mosquitoes. We then demonstrated this in the lab, showing that binary synergism between heat and host odor drives host attraction in the absence of CO2 detection. When CO2, heat or body odor are presented alone to mosquitoes these single cues do not elicit appreciable host-seeking or blood-feeding behavior. However, presenting any two of the three cues during tests is sufficient to trigger these behaviors, meaning that multiple additional host cues make up for a lack of CO2 detection in Gr3 mutant mosquitoes.

Figure 2:  A female Aedes aegypti mosquito blood feeding from the author's arm. Photo credit Benjamin Matthews with assistance from Conor McMeniman.

We suggest that such multi-sensory integration may have evolved to allow mosquitoes to efficiently home in on a live host. Importantly this finding suggests that control measures should target multiple mosquito sensory pathways to stop these blood-sucking insects from finding us.

Reference

Multimodal integration of CO2 and other sensory cues drives mosquito attraction to humans. McMeniman CJ, Corfas RA, Matthews BJ, Ritchie SA, Vosshall LB. Cell 2014;156(5): 1060-71. Pubmed PMID: 24581501.

Pubmed link

Link to Cell article

Link to mini review in Cell