Mosquitoes use trio of senses to track humans

Mosquitoes track down their human targets by making use of a multi-sensory strategy that involves odours, visual cues and body heat to draw them closer to their prey, a new study has found.
While bug repellents and lighting citronella candles may keep the mosquitoes at bay for a while, but no solution is perfect because the pests have evolved to use a triple threat of visual, olfactory, and thermal cues to home in on their human targets, researchers said.
When an adult female mosquito needs a blood meal to feed her young, she searches for a host - often a human.

Many insects, mosquitoes included, are attracted by the odour of the carbon dioxide (CO2) gas that humans and other animals naturally exhale.
However, mosquitoes can also pick up other cues that signal a human is nearby. They use their vision to spot a host and thermal sensory information to detect body heat.
To find out how and when the mosquitoes use each type of sensory information, researchers from the California Institute of Technology in US released hungry, mated female mosquitoes into a wind tunnel in which different sensory cues could be independently controlled.

In one set of experiments, a high-concentration CO2 plume was injected into the tunnel, mimicking the signal created by the breath of a human.

In control experiments, the researchers introduced a plume consisting of background air with a low concentration of CO2.
For each experiment, researchers released 20 mosquitoes into the wind tunnel and used video cameras and 3-D tracking software to follow their paths.
Information gathered from these experiments enabled the researchers to create a model of how the mosquito finds its host over different distances.
They hypothesise that from 10 to 50 meters away, a mosquito smells a host's CO2 plume.
As it flies closer - to within 5 to 15 meters - it begins to see the host.
Then, guided by visual cues that draw it even closer, the mosquito can sense the host's body heat. This occurs at a distance of less than a meter.

"Understanding how brains combine information from different senses to make appropriate decisions is one of the central challenges in neuroscience," said Michael Dickinson, the principal investigator of the study.
"Our experiments suggest that female mosquitoes do this in a rather elegant way when searching for food. They only pay attention to visual features after they detect an odour that indicates the presence of a host nearby. This helps ensure that they don't waste their time investigating false targets like rocks and vegetation," said Dickinson.
The work provides researchers with exciting new information about insect behaviour and may even help companies design better mosquito traps in the future.

The study appears in the journal Current Biology.