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
The internets have been abuzz with this photo today:
It’s a photo of an aluminum cast of an ant nest made by Walter Tschinkel, a Florida entomologist–but there haven’t been a lot of additional details.
The nest you are looking at is one of a Florida harvester ant, and appeared with many other photos and casts in a 2004 paper about nest architecture in the Journal of Insect Science. They are things of great beauty, and tell us a lot about how ants build.
This series of photos, for example, shows how the complexity of the nest structure grows as the colony adds workers. You can find more amazing photos of different types of ant nest casts here in a 2012 article.
There is even a video of the process of making these casts! And yes, don’t do this at home. Even if Dr. Tschinkel did publish detailed instructions on all the different ways to make an ant nest cast. I am looking at you, Mr. Treelobster.
I would be remiss if I did not also link to this older video that uses ten tons of cement to discover the extent of a much larger
African South American ant nest. (I am told it’s Atta vollenweideri, and it was dug up in South America. Thanks for the correction!)
Tschinkel W.R. (2004). The nest architecture of the Florida harvester ant, Pogonomyrmex badius., Journal of insect science (Online), PMID: 15861237
Tschinkel W.R. (2010). Methods for Casting Subterranean Ant Nests, Journal of Insect Science, 10 (88) 1-17. DOI: 10.1673/031.010.8801
Earlier this week, the internets were buzzing with a claim that Kickstarter is funding more projects than the National Endowment for the Arts. It turns out that may not be strictly true, but it certainly is true that a lot of cool projects are being crowd-sourced that otherwise would never have made it off the ground.
I’ve mentioned some insecty Kickstarter projects before, like Meet The Beetle (a film about an endangered tiger beetle). Unfortunately, Kickstarter is limited to arts and humanities. But now the concept of crowdsourcing has been harnessed for science!
“Unique” doesn’t begin to describe Madagascar. This giant island split from the African Continent over 160 million years ago, and over 90% of it’s mammal and reptile species occur no where else in the world. Deforestation and erosion are critical threats to the island’s ecosystems, and many native species are endangered.
Brian Fisher, one of the folks behind AntWeb, is leading a project to document the ant species of a high remote preserve. You might be wondering why you should care about ants in Madagascar. You may especially be wondering this because you have figured out that at some point later in this post I’m going to hit you up for a donation. I really like this statement from AntWeb that puts ants in context:
“At this moment, more than one thousand trillion ants are scurrying all over the Earth. If every human climbed aboard one side of a scale, and every ant crawled onto the other side, the scale would just about balance.”
Ants probably move more earth and recycle more dead things yearly than a whole army of human undertakers with bulldozers ever could. Ants are a critical part of making the world’s living systems function. The project description:
“Ants are the glue that hold forests together. But Madagascar’s hotspots of biodiversity are vanishing, and along with them unknown species. An estimated 40 percent of the island’s species, in fact, have already perished through human encroachment.
While ants aren’t as popular as furry and feathery animals, the insects turn over forest soil, breakdown debris, disperse crucial nutrients and otherwise support an unimaginable number of species both up, down and across the food chain. The insects are also a growing resource for antimicrobial and antifungal compound discovery, as many ants manufacture such chemicals to ward off disease and even farm food.
I need to reach one of the last standing pristine forests, called the Kasijy, before nearby populations burn them down to raise cattle. Researchers have visited the remote site only a handful of times because it’s a rugged, canyon-filled landscape resting on high blocks of limestone and sedimentary rock.Because Kasijy is so pristine, it also serves as a crucial data point of what Madagascar used to be like before the advent of modern civilization. The region and other forests are great places to understand the ongoing impacts of climate change on highly specialized ecosystems.
My expedition aims to:
- Inventory Kasijy’s untold new species and document their roles in a pristine natural ecosystem.
- Understand the biodiversity patterns of Madagascar and resolve our “bioilliteracy” of the Kasijy forest.
- Set up more robust conservation plans for the island.
- Raise awareness of Madagascar’s natural wonders and its ongoing plight.”
There are 39 days left to fund this project–I hope you can spare a dollar or two to help a researcher out! Note that a large gift gets you acknowledged in any manuscripts published from this research.
You might have noticed a lot of news lately about robot designs based on insects. Insects are great models for robots because bugs have an extremely stable and efficient model of locomotion: the tripod gait. At any time, roaches have 3 feet on the ground–even when they’re running. This tripod structure makes insects extra-resistant to tripping or tipping over.
Biomimetics is the fancy name for engineering systems that copy principles found in nature. Basing robots that need to scamper over rough terrain on an insect model that’s successfully lasted millions of years makes a lot of sense. But just how, exactly, do insects keep all those legs going in the right direction? How can they respond so quickly to an approaching rolled-up newspaper? How do insects manage this advanced scuttling with such a tiny brain? And how can insects keep running even after their head is removed?
(Yes, insects can live for quite a while without a head. They eventually die from dehydration or starvation because they can’t drink or eat anymore, but remain able to run away and respond to environmental stimuli. It’s really quite disturbing.)
In order to build a biomimetic robot, one has to first understand the mechanics at work in insects. The engineering explanation for insect locomotion is hidden in equations about viscoelastic spring mass oscillation and tiny insect-mounted cannons.
This is not a photoshopped picture; it’s from a 2002 research paper in which researchers attempted to mathematically work out the principles of roach locomotion. You can see the jet-pack at work in this movie:
So. Um, WHY did they put jetpacks on roaches? Aside from it just being a totally freakin’ COOL thing to do?
Remember I mentioned how stable the tripod gait is? The researchers suspected that the roach wasn’t using just its brain to keep itself balanced and running. They created a mathematical model of a roach with legs that were springs.
Just the mechanical properties of springy legs were able to explain how a roach kept on track and at full speed, despite obstacles. They called these “preflexive” mechanisms, to indicate that the exoskeleton and muscles stabilize roaches without involvement of the nervous system.
They had an explanation on paper, with a lot of big words and calculations of lateral velocity. The next step was to test their lovely model by poking a roach while it was running. That…was about as difficult to do as you might imagine, based on your experience chasing roaches around your kitchen.
The researchers needed to have a precisely measured force disturbing the roaches, so that they could plug it into their model and see if it was accurate. Hence, a tiny exploding cannon mounted on a roach. Or, to give it the gizmo it’s proper name, the rapid impulsive perturbation (RIP) device. (That name is doubly clever, since they were experimenting with the death’s head cockroach, Blaberus discoidalis.)
They calculated the lateral force generated by the RIP explosion was equal to 85% of the insect’s forward motion. If you were jogging along, and I ran into you with a force that was 85% of your forward momentum, I don’t think either of us would be standing up. (Ok, yes, there’s mass involved in this too, but just work with me here.) The roaches hardly even break stride. In fact, it took just 13 miliseconds for a roach to begin to respond to the explosion and get back on track. The roaches completely recovered from that RIP explosion within 31 miliseconds.
Insects are indeed pretty damn amazing animals, and a great model for robotics. The authors have continued their work on the hexapod gait, and have proposed several models of ways in which legs might be built–in both roaches and robots–to respond quickly to problems.
Science is awesome.
Citation: Jindrich DL, & Full RJ (2002). Dynamic stabilization of rapid hexapedal locomotion. The Journal of experimental biology, 205 (Pt 18), 2803-23 PMID: 12177146
Revzen S, Koditschek DE, & Full RJ (2009). Towards testable neuromechanical control architectures for running. Advances in experimental medicine and biology, 629, 25-55 PMID: 19227494
Also: Just look at how easily the Star Wars AT-AT or AT-STs were destroyed by the rebels! Tripod-gait woud have saved the empire!
I usually like Lifehacker, but in this case, FAIL. Here’s a story they ran 2 weeks ago:
Bounce Fabric Softener Keeps Mosquitoes and Gnats Away
Some people have sworn by the power of Bounce dryer sheets—and specifically Bounce, too—to keep mosquitoes away from them, and gnats out of their garden. Now scientists have proven the power of fluffy white sheets as an insect repellent.
Lifehacker wasn’t the only media group that picked up on this story; and pretty much all of them made the same mistake.
When you look at the actual research paper, what you see is that some of what was reported was correct. There actually WAS a paper that examined the repellency of Bounce dryer sheets to insects.
Raymond A. Cloyd, et al. (2010). Bounce® Fabric Softener Dryer Sheets Repel Fungus Gnat, Bradysia sp. nr. coprophila (Diptera: Sciaridae), Adults.
HortScience, 45, 1830-1833
There is a very large difference between a fungus gnat and a mosquito. That’s rather like reporting that the care and feeding of cats and humans are interchangeable. Since, you know, we’re all mammals, right?
Let’s start with what a fungus gnat is, and when you’d be likely to encounter them.
Basically, fungus gnats don’t bite. They just annoy. They’re likely to be the tiny things flitting around the soil of your potted plants. They can be a commercial pest in greenhouses, but generally they are just a nuisance. They breed in moist soil and nibble on roots.
I think everyone knows what mosquitoes are–a biting fly that can carry major human diseases. They breed in water and adult females require a blood meal from a host to reproduce.
Not. The. Same.
This is an important difference, and it is a difference that has human health implications. If you go out in an area where there are disease-carrying mosquitoes with just a pocket full of dryer sheets as your protection, you are taking a risk with your health.
Media make mistakes covering science news all the time–but in this case, it’s a taxonomic mistake that could literally cost someone their life. (Ok, I’m overstating it a bit. But, in THEORY, I’m right.)
Now that I’ve impressed upon you what’s at stake, let’s look at the actual experiment, shall we?
The authors tested the repellency of the dryer sheets in a very controlled situation, and were successful at reducing the number of fungus gnats in test chambers containing a dryer sheet. At the end of their paper there is this caveat:
However, there are still important issues that need to be resolved, including the residual effects (based on age of dryer sheets) and effective distance of repellency, response in a no-choice situation (if dryer sheets are placed into each petri dish), impact on fungus gnat larval populations, and ultimately plant damage.
Now, every scientific paper ends this way. Here’s what we did, and here’s how it’s uncovered a whole host of new questions for us to answer! Continued employment, yay!
What I, as a gardener, would draw from this experiment is that it certainly couldn’t hurt to put a Bounce fabric sheet near my potted plants, if I happened to have a fabric sheet laying around.
But I would not, in a bajilion years, jump to the conclusion that it would protect me from all biting insects.
Long link to the paper, since the Researchblogging code keeps messing up blog code
Raymond A. Cloyd, et al. (2010). Bounce® Fabric Softener Dryer Sheets Repel Fungus Gnat, Bradysia sp. nr. coprophila (Diptera: Sciaridae), Adults. HortScience, 45, 1830-1833