How Mosquitoes Track Their Human Targets, Study Explains

Mosquitoes have an uncanny ability to track their human targets by using a multiple sensory strategy involving visual cues, odours and body heat to draw closer to the prey, according to a new study. While use of bug repellents and lighting citronella candles can potentially keep the mosquitoes at bay for a certain period of time, but no perfect solution appears to be available presently since the pests use a multipronged system comprising of olfactory, visual and thermal cues to attack their human targets, according to the researchers.

 

When a blood meal is needed by an adult female mosquito to feed her offspring, she goes out in search of a host and that often times, is a human.  The odour of carbon dioxide exhaled by humans as well as other animals often attracts insects including mosquitoes. However, mosquitoes can pick up additional cues that signal the proximity of a human. They employ their vision to spot the host and use thermal sensory information for detecting body heat.

Researchers from California Institute of Technology, US released mated and hungry female questions into a wind tunnel equipped with different sensory cues with independent controls to examine when and how the mosquitoes used each sensory information.

Highly concentrated carbon dioxide plume was injected into the tunnel in one experiment to mimic the signal generated by the breath of a human. In other control experiments researchers employed a plume with low carbon dioxide concentration and background air.
20 mosquitoes were sent into the tunnel for each of the experiments and 3-D tracking software with video cameras was used to follow the path of the mosquitoes.

Information culled from these experiments equipped researchers with information needed to create a model of how the mosquitoes could find its host over varying distances.  The resulting hypothesis is that the mosquitoes can smell carbon dioxide plume of hosts from distances between 19 and 50 meters. Therefore, it starts seeing the host as it gets closer to 6 to 15 meters radius. Subsequently the mosquitoes sense the body heat of the target after drawing closer with the help of visual cues.

Michel Dickinson, principal investigator of the study says that comprehending how brain combines information from multiple senses to make appropriate decisions is a central challenge to neuroscience.

He added further that the present experiments suggest female mosquitoes were able to do this more elegantly in their quest for food. This is because they focus on visual features once they have detected an odor indicating the presence of host in the vicinity. This way they also don’t track false targets like vegetation and rocks.