Can mosquitoes learn to love DEET?
When it comes to keeping mosquitos from biting, DEET has long been considered the gold standard. Sprayed on before hikes and picnics and while traveling to mosquito-dense corners of the globe, the world’s most widely used insect repellent comes with the expectation that its smell will send mosquitoes zipping off in the opposite direction.
But research published
yesterday in the Journal of Experimental Biology suggests that
mosquitoes may learn to associate the smell of DEET with dinner—and start
gravitating toward it instead of away from it. The findings challenge long-held
assumptions about how DEET works and what mosquitoes may be capable of
learning.
Training changed how mosquitoes react to DEET
For the study, researchers from the University of Tours in
France and Virginia Tech examined whether female Aedes aegypti mosquitoes,
the species that spreads dengue, Zika, yellow fever, and chikungunya, could
learn to associate DEET with a food reward.
The team used a form of Pavlovian conditioning in which
mosquitoes feed on warm blood through an artificial membrane. Twenty seconds
into their meal, the researchers released DEET into the feeding enclosure—a
process they repeated three more times before exposing the mosquitos to DEET
but no food reward.
When the trained mosquitos caught a whiff of DEET alone, more than 60% of them tried to feed again, displaying what researchers termed a “biting attempt response” (BAR). That’s compared with roughly 20% of untrained mosquitoes who performed BAR when exposed to DEET alone.
In another experiment, mosquitoes were given a choice
between two human hands. One hand was treated with DEET, and one was untreated.
All of the untrained mosquitoes avoided the DEET-treated hand. Trained
mosquitoes, however, were significantly more likely to orient toward the
treated hand.
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