There’s been a lot of reporting about new research about the insect repellent DEET this week. Unfortunately, some of the media didn’t quite get it right. Headlines like this one were common…and completely wrong.
The media coverage left a lot of people confused about DEET, and if it still worked. The results of the research were a lot more nuanced than “DEET suddenly stopped working so we are all screwed.”
Here is what the average person being bitten by mosquitoes needs to know, condensed:
DEET still works fine. It’s still one of the best insect repellents out there. We know a way it might become less effective now, as demonstrated in the laboratory.
The un-condensed version:
DEET is one of our oldest and best insect repellents. It’s universally acknowledged as the best repellent around, and has broad activity against several types of biting flies and ticks. This is why a problem with DEET is big news–it’s invaluable in preventing transmission of several different diseases.
Amazingly, scientists are just beginning to understand how DEET works, even though it’s been in widespread use for 50 years. We know it stops ticks and mosquitoes from biting, but the exact mechanism of how that happens is still not clear. Does it make us ‘invisible‘ by blocking mosquitoes from smelling? Does it smell horrible to biters? It’s still not settled science yet.
That’s important to know, since if we know how something works, we can copy it and try to make new and better controls. There is always a concern with evolution of resistance in insects–they are commonly used to study genetics and mutations for a reason. Insects breed fast, and they breed often–which means that small genetic changes, if they are helpful at keeping a bug alive and having sex, can spread quickly through a population.
Resistance to DEET, our most powerful and broad spectrum insect repellent, would be a very bad thing. And so it makes sense that entomologists interested in human health would be studying how DEET works.
Evidence of genetic resistance to DEET in mosquitoes has actually been around since 1994. In 2010, researchers found that they could increase the frequency of a gene that made mosquitoes ignore DEET to 50% in a couple of generations. That’s alarming, but that was in a laboratory-bred colony.
‘Laboratory-Bred’ is an important distinction for both that study and the recent one. Mosquitoes in a cage have only one source of food (often the hapless graduate student that is rearing them). They can’t fly off and look for other people or animals to bite. It also means that their sexual choices are limited to other mozzies in the cage, so resistance can evolve more quickly that it would out in the wild where they have a wider choice of hookups.
Scientists use work in the lab to model the real world. It helps us understand how organisms grow, change, and respond to their environment. That doesn’t mean that it’s a firm prediction of what will happen out in the larger world, especially with a group as diverse and wily as mosquitoes. That’s why I think headlines like the one at the top are irresponsible, and mangling the message of the research.
You can see an interview with one of the researchers here; note she is careful to repeat that we should not discard DEET wholesale on the results of this research!
“What this work indicates is that there may potentially at some point in the future be some problems with the repellents that we have, that we need to be aware of in advance. Possibly we can use this information to alter the repellent DEET to make it more effective, it may also help us in finding new repellents because we will know if [mosquitoes] are able to overcome certain things……Even though repellents are working fantastically at the moment, what this tells us is maybe how to prevent problems cropping up, and how to alter things for the future to make them more effective.” [emphasis mine]
- CDC list of recommended insect repellents
- Mosquito repellent clothing (uses a different chemical than DEET)
Articles referenced in this post:
- Stanczyk N.M., Brookfield J.F.Y., Field L.M., Logan J.G. & Vontas J. (2013). Aedes aegypti Mosquitoes Exhibit Decreased Repellency by DEET following Previous Exposure, PLoS ONE, 8 (2) e54438. DOI: 10.1371/journal.pone.0054438.t001
- Ditzen M., Pellegrino M. & Vosshall L.B. (2008). Insect Odorant Receptors Are Molecular Targets of the Insect Repellent DEET, Science, 319 (5871) 1838-1842. DOI: 10.1126/science.1153121
- Jaramillo Ramirez G.I., Logan J.G., Loza-Reyes E., Stashenko E., Moores G.D. & Vontas J. (2012). Repellents Inhibit P450 Enzymes in Stegomyia (Aedes) aegypti, PLoS ONE, 7 (11) e48698. DOI: 10.1371/journal.pone.0048698.t003
- Rutledge L.C., Gupta R.K., Piper G.N. & Lowe C.A. Studies on the inheritance of repellent tolerances in Aedes aegypti., Journal of the American Mosquito Control Association, PMID: 8014634
- Stanczyk N.M., Brookfield J.F.Y., Ignell R., Logan J.G. & Field L.M. (2010). Behavioral insensitivity to DEET in Aedes aegypti is a genetically determined trait residing in changes in sensillum function, Proceedings of the National Academy of Sciences, 107 (19) 8575-8580. DOI: 10.1073/pnas.1001313107