We all work (or have worked) hard to afford a nice day on the beach, at the park, or just a day of ambiguous leisure. We sometimes work even harder to protect ourselves from the malheurs of pests, namely the winged sort we’ve named mosquitoes. But resistance may be futile, for a mosquito can sense heat, can smell humans, and can see you, too. That’s three senses working against you. No wonder they’re so persistent.
HELL HATH NO FURY LIKE a MOSQUITOES’ MOTHERS’ SCORN
The most ravenous mosquito is the new mother, who seeks a blood meal to feed her younglings. Her favorite host is human. A wide variety of insects including mosquitoes can detect and are attracted to the smell of carbon dioxide (CO2) that we exhale. And that’s not all; mosquitoes can also use thermal sensory data to detect a suitable host of blood, and when all else fails, there’s always old-fashioned sight. But who would imagine themselves using each one of their senses in a sequence, especially when one’s own survival depends on putting them to work together?
DO PESTS INTEGRATE SENSES?
In order to discover precisely how mosquitoes balance such a barrage of senses, a recent study was performed. In the study, researchers set hungry, mated female mosquitoes free into a wind tunnel. This wind tunnel was jerry-rigged for scientists to control which sensory cues occurred.
Each experiment featured 20 mosquitoes, who were all inserted into the tunnel and filmed with 3D tracking software. When a plume of air heavy in CO2 concentration was released, the mosquitos followed it, just as the scientists predicted. A plume with normal background air did not seem to pique the mosquitoes’ interest.
TRANSPOSING HYPOTHESES FROM OTHER FINDINGS
Floris van Breugel, a postdoctoral scholar in the lab of Michael Dickinson, professor of bioengineering at the California Institute of Technology, found that animals (specifically, fruit flies), are more attracted to visual features, even when exposed to an attractive odor.
“This was a new finding for flies, and we suspected that mosquitoes would exhibit a similar behavior. That is, we predicted that when the mosquitoes were exposed to CO2, which is an indicator of a nearby host, they would also spend a lot of time hovering near high-contrast objects, such as a black object on a neutral background.”
ARE MOSQUITOES’ SENSES BIASED?
To test Dickinson’s idea, the scientists repeated the CO2 plume experiment, with a slight change in environment: they placed a dark object on the floor of the wind tunnel. The scientists discovered that even with heavy CO2 plumes, the pests were more attracted to the dark, high-contrast set piece. But, when there was no CO2, the same insects showed no interest in the darkness.
What this means is that the effect of mosquitoes’ olfactory systems is not dissimilar to our suffering. The mosquitoes smell CO2, begin their flight, and continue on well beyond the CO2 towards visual stimulation, which is more temporary, because they carry on the memory of CO2 with them. Mayhaps we should take a matador instead of bug spray for our next camping trip.