DEET may – From bean plants calling in wasps when caterpillars strike to lab-trained mosquitoes learning to approach DEET, the science stories share a hard lesson: defenses built for instincts can be tested—and sometimes outmaneuvered—by learning, timing, and chemical cu
The moment it stops working isn’t always sudden. Sometimes it’s a surprise the body learns, reward by reward, cue by cue.
On one side of the biological battlefield, common bean plants may be doing something that looks a lot like reconnaissance. When caterpillars munch on bean plants. a compound in the caterpillar spit triggers the plants to release a chemical signal into the air. Researchers described this chemical counterattack in a study out this week in the journal Science Advances. The signal functions like a distress flare: it attracts predatory wasps and parasitoid wasps—some that eat the caterpillars. others that lay eggs inside the caterpillars’ bodies so their babies can remove the threat from within. The plant isn’t simply reacting to any damage. While plants commonly release chemical signals after wounds. the specific compound that draws in wasps is triggered via caterpillar spit. not by cutting a leaf or damaging the plant another way.
On the other side, a familiar mosquito repellent—DEET—faces a different kind of challenge: not a new chemical enemy, but mosquito learning.
DEET is known as a key ingredient in many mosquito repellents. and it is widely used to help prevent itchy bites and. crucially. disease transmission. In the lab, however, mosquitoes were trained to associate the smell of DEET with feeding. The work. published recently in the Journal of Experimental Biology. took a step further than earlier research showing that repeatedly exposing mosquitoes to DEET can make them less repelled by it. Clement Vinauger. a neuroethologist at Virginia Tech who worked on the study. said in the transcript that DEET generally works because mosquitoes repel from it—researchers just haven’t fully pinned down the exact mechanism for why it repels.
So the researchers asked a more pointed question: could mosquitoes be taught to want it?
They turned to a Pavlovian approach. Instead of ringing a bell, they used the smell of DEET. And instead of food for a dog. they used a reward mosquitoes could actually bite and feed on—either a bag of blood or sugar. The training worked. In a little over half of the trials. mosquitoes began to associate DEET with feeding time. and they would actively approach DEET even when the reward wasn’t there. When tested with actual humans. the trained mosquitoes also gravitated toward a person’s hand sprayed with DEET more than toward the other hand without the repellent.
That result is the kind of finding that makes people pause, even if they’ve never thought about their own chemistry as a learning signal. In the transcript, the confusion comes through plainly: if DEET is supposed to repel mosquitoes, why would it be something they approach?
The answer. in the researchers’ framing. is that this kind of learned attraction may require conditions that don’t typically happen outside the lab. Ali Afify. an entomologist and neuroscientist at Drexel University who was not involved in the study. pointed out that it’s unclear whether this could happen in the wild. Because mosquitoes are not attracted to DEET in real life. he said. it’s very difficult for them to experience DEET while blood feeding. And for now, the study’s takeaway is direct: don’t stop using DEET. The researchers emphasize that it remains a very effective repellent in real-world situations.
Still, the thread connecting these stories is hard to miss. Plants appear to defend themselves by deploying very specific chemical cues when caterpillars attack. Mosquitoes, at least under training, can learn to treat a repellent smell as a pathway to feeding. Even the other science story in the same roundup—about speeding up learning in mice—leans into that same uncomfortable reality: what you feed the brain. and how you time it. changes what an animal learns.
In experiments published in the journal Science, researchers found that giving bigger rewards less frequently helped mice learn faster. Josh Dudman. one of the study’s authors. said they had been underestimating how efficiently animals can learn. describing how researchers could move some of the slowest learners all the way up to the fastest learners. In that work. the reward was artificially sweetened water. and the animals learned both a Pavlovian cue—sounds linked to reward—and tasks
like pulling a joystick or turning a tiny steering wheel right or left to get a reward.
Taken together, the roundup lands less like a list of neat discoveries and more like a warning written in biology’s own handwriting: defenses don’t just have to be strong—they have to remain strong in the face of learning, timing, and the cues animals pay attention to.
DEET mosquitoes learning parasitoid wasps bean plants caterpillars chemical signals Journal of Experimental Biology Science Advances Science dopamine Pavlovian conditioning