It's a warm summer night, and you go outside prepared for the onslaught of bugs with a bug spray containing DEET. But that spray could just be marking you as a feeding ground if you don't apply it regularly, according to a new study.
A new study by Virginia Tech, published in the Journal of Experimental Biology, suggests that mosquitoes may be able to learn to associate DEET with food, and even become attracted to it.
"If someone applies DEET and the concentration fades over time, but a mosquito still manages to feed, the insect may begin associating that smell with a reward," said Vinauger, part of the Department of Biochemistry in the College of Agriculture and Life Sciences.
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The university's study focused on the yellow fever mosquito, Aedes aegypti, a species of bug that spreads Zika, yellow fever, and other infections that impact millions of people each year.
Researchers trained the mosquitoes using Pavlovian conditioning, made famous by a dog learning to associate a bell's ring with food.
The mosquitoes were restrained behind fabric mesh, and once they began to feed on a warm blood bag, they were introduced to the smell of DEET.
However, after repeating the experiment, researchers say more than 60% of the insects tried to feed only when presented with the smell of DEET.
The study went further, presenting two human hands to the mosquitoes. One hand was untreated, and the other was coated with DEET at normal concentrations. Researchers say the untrained mosquitoes would avoid the hand with DEET, while trained mosquitoes appeared to be drawn to it.
Researchers also performed the experiment with mosquitoes being given access to sugar instead of blood, and the same association was present.
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“The common assumption has always been that repellents work because of their chemistry — that DEET simply smells bad to mosquitoes and they flee or that its chemistry prevents mosquitoes from smelling us,” said Vinauger, who is also an affiliate of Fralin Life Sciences Institute's Center for Emerging, Zoonotic, and Arthropod-borne Pathogens. “But what we are showing is that the mosquito’s brain can rewrite that response based on experience. What the insect has learned matters just as much as what the chemical does. That, I think, is a paradigm shift.”
Don't go throwing out that DEET bug spray, though. Researchers say that the findings don't mean people should stop using DEET, but rather that timing and the concentration of the repellent may matter more than previously thought.
"Instead of applying a lot at once, you may want to reapply regularly so it's always active and providing continuous protection," Vinauger said.
