On summer evenings, we try our best to avoid mosquito bites by dousing our skin with bug repellents and lighting citronella candles. These efforts 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, a new Caltech study suggests. The study, published by researchers in the laboratory of Dr. Michael Dickinson, the Esther M. and Abe M. Zarem Professor of Bioengineering, was published online on July 16, 2015 in Current Biology. The article is titled “"Mosquitoes Use Vision to Associate Odor Plumes with Thermal Targets." 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 odor 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. But how do the mosquitoes combine this information to map out the path to their next meal? To find out how and when the mosquitoes use each type of sensory information, the researchers 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.
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