Mosquito magnets

My wife claims that I only bring her along on tropical vacations to lure the mosquitoes away from me.

She is, to put it bluntly, a mosquito magnet.  If there's an outdoor party, and there is a single lonely mosquito anywhere within a five-mile radius, it will find her.  Worse still, she has a bad allergic reaction to bites; being bitten leaves her itching for days.

Bad combo, that.

I, on the other hand, barely get bothered at all.  The same strange dichotomy got passed to our kids; our older son doesn't seem to get bitten much.  On the other hand, we took a family vacation to Belize when our boys were twelve and fifteen, and I saw our younger son was sitting on his bed one evening examining his legs.  I asked him what he was doing.

Turned out he was counting mosquito bites.  He lost count at around forty.

[Image licensed under the Creative Commons User:Ngari.norway, Mosquito bite4, CC BY-SA 3.0]

The contention that many have, of some people being more attractive to mosquitoes than others, was just demonstrated conclusively in a paper last week in the journal Cell, by a team led by Leslie Vosshall of the Howard Hughes Medical Institute.  What Vosshall and her team did was to have volunteers wear nylon stockings on their arms for six hours, allowing the fabric to pick up any chemicals the person was secreting in their sweat and skin oils.  The nylons were then cut up into squares, and the pieces presented to hungry Aedes aegyptii mosquitoes.

The results were unequivocal.  One subject, #33, had an attractiveness to mosquitoes over a hundred times greater than the least attractive subjects, #19 and #28.

What seems to set apart people like poor #33 is the particular cocktail of carboxylic acids in their skin oils.  Carboxylic acids are small organic molecules characterized by having a carboxyl group -- a carbon atom double-bonded to an oxygen atom and single-bonded to a hydroxyl (-OH) group -- and include such familiar compounds as amino acids and fatty acids.  It turns out that of the hundreds of different kinds of carboxylic acids, each person produces different ones in different amounts -- and this "scent" (not that you or I would notice the difference) is what determines who is a mosquito magnet, and who largely gets left alone.

A little discouraging, though, is their other finding; that this chemical signature is relatively resistant to changes in diet and grooming habits.  None of the contentions you might have heard -- eating foods rich in B vitamins, using unscented soaps and shampoos, and so on -- seemed to make any difference.  The people who were mosquito attractors stayed that way throughout the course of the experiment, regardless what they ate and what cosmetic products they used.

While this study might eventually lead to better repellents, at the moment, we're kind of stuck where we were.  The best mosquito repellent is DEET (diethyltoluamide), which has a pretty good track record for safety, although (as I found out when I was in Ecuador) dissolves plastics.  (Fortunately, the only thing damaged was a ball-point pen; I discovered this when I applied some mosquito repellent, picked up the pen, and it promptly stuck to my hand.)  Some other products, like Avon's "Skin So Soft," seem to have some effect but aren't nearly as reliable as DEET.  

Maybe if Vosshall and her team can pinpoint exactly which carboxylic acids are causing the problem, they could find some kind of repellent that would work by blocking them or breaking them down.  I know my wife would appreciate it.  It's late October in upstate New York, and the eight mosquitoes still left alive around here are still waiting by our back door for one last chance to bite her.

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Buzzing off

I have great respect for scientists, which I hope is obvious from the content of this blog.  Even so, there are times I read scientific research and say, "What the hell were they thinking?"

That was my first thought when I read a BBC News article claiming that playing dubstep music by Skrillex makes mosquitoes less likely to bite and mate.  If you don't know who Skrillex is, that's probably a good thing if you've got reasonably refined musical sensibilities.  I try to be tolerant of other people's musical tastes and acknowledge that what you like is a matter of opinion, but it is my considered judgment that Skrillex sounds like a robot having sex with a dial-up modem.

So apparently what they apparently did is to play Skrillex for some mosquitoes, and the mosquitoes apparently didn't feel like eating or mating, which I have to admit is kind of the effect it has on me.  "[T]he occurrence of blood feeding activity was lower when music was being played," the scientists write.  "Adults exposed to music copulated far less often than their counterparts kept in an environment where there was no music...  The observation that such music can delay host attack, reduce blood feeding, and disrupt mating provides new avenues for the development of music-based personal protective and control measures against Aedes-borne diseases."

[Image licensed under the Creative Commons, Aedes aegyptii, photograph taken by Muhammad Mahdi Karim]

When I finished reading the article, my first thought was that this was a typical sensationalized report on scientific research, where popular media completely misrepresents what the scientists did in order to get clicks.  Sadly, this is not the case.  The BBC News actually did a pretty good job of describing the research -- it's just that the research was kind of... um... terrible.

Here's a piece from the paper itself, which appeared in Acta Tropica last week and is entitled,
"The Electronic Song 'Scary Monsters and Nice Sprites' Reduces Host Attack and Mating Success in the Dengue Vector Aedes aegypti," by a team of researchers led by Hamady Dieng of the University of Malaysia:

Sound and its reception are crucial for reproduction, survival, and population maintenance of many animals.  In insects, low-frequency vibrations facilitate sexual interactions, whereas noise disrupts the perception of signals from conspecifics and hosts.   Despite evidence that mosquitoes respond to sound frequencies beyond fundamental ranges, including songs, and that males and females need to struggle to harmonize their flight tones, the behavioral impacts of music as control targets remain unexplored. In this study, we examined the effects of electronic music ("Scary Monsters and Nice Sprites" by Skrillex) on foraging, host attack, and sexual activities of the dengue vector Aedes aegypti.   Adults were presented with two sound environments (music-off or music-on).  Discrepancies in visitation, blood feeding, and copulation patterns were compared between environments with and without music.  Ae. aegypti females maintained in the music-off environment initiated host visits earlier than those in the music-on environment.  They visited the host significantly less often in the music-on than the music-off condition.

Which is pretty much what the BBC News article said.

What's wrong with this research is that it falls into what I would call "so what?" studies.  It's the kind of thing that even if the protocols and controls were appropriate, doesn't tell you very much.  Okay, Skrillex screws up mosquitoes.  Why?  They only did "music on" and "music off;" they didn't try different kinds of music, various pure tones, harmonics, combinations of sounds, and other sorts of sounds.  So the outcome really gives us very little information about what's actually going on, and why -- nor how this could be used to reduce the spread of mosquito-borne diseases.

Because frankly, if I had a choice of getting dengue fever and listening to Skrillex all day, I'd have to think about it.

So anyhow, I guess having a paper in a scientific journal doesn't necessarily guarantee that the research it describes isn't kind of silly.  And it also highlights the importance of going from the account in the popular media to the research itself before making a judgment.  Most of the time, if there's a problem or a misrepresentation, it's the popular media that's at fault.

But not always.  So if you want to repel mosquitoes, you might want to do your own experiments.  There must be a better way than subjecting yourself and everyone around you to dubstep.

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This week's Skeptophilia book recommendation combines science with biography and high drama.  It's the story of the discovery of oxygen, through the work of the sometimes friends, sometimes bitter rivals Joseph Priestley and Antoine Lavoisier.   A World on Fire: A Heretic, an Aristocrat, and the Race to Discover Oxygen is a fascinating read, both for the science and for the very different personalities of the two men involved.  Priestley was determined, serious, and a bit of a recluse; Lavoisier a pampered nobleman who was as often making the rounds of the social upper-crust in 18th century Paris as he was in his laboratory.  But despite their differences, their contributions were both essential -- and each of them ended up running afoul of the conventional powers-that-be, with tragic results.

The story of how their combined efforts led to a complete overturning of our understanding of that most ubiquitous of substances -- air -- will keep you engaged until the very last page.

[Note:  If you purchase this book by clicking on the image/link below, part of the proceeds will go to support Skeptophilia!]

Zika freakout

Can we once, just once, face a problem in the world and find a solution based in logic?  And, fer cryin' in the sink, not ascribe it to a conspiracy?

I am referring, of course, to the Zika virus, which is currently exploding in the tropics, and is suspected of being connected to microcephaly and low brain development in infants born to infected women, and also cases of the neurological disease Guillain-Barré syndrome.  (Nota bene: these connections are still tentative, and are being studied.  The evidence thus far indicates possible links, but establishing causation and finding an underlying mechanism in either case have yet to be accomplished.)

Of course, a viral disease carried by mosquitoes, with uncertain and possibly devastating consequences for the victims through an unknown mechanism, opens the door for wild speculation.  And the conspiracy-minded amongst us have certainly been quick to rise to the occasion.

First, we have the claim that Zika was caused by the release of genetically-modified mosquitoes by Oxitec Inc., a biotechnology firm -- in some versions of the story, caused deliberately for the purposes of population control.  And since no conspiracy is complete without a powerful rich guy controlling the whole thing, the originator of this evil master plan is...

... none other than Bill Gates.

So, the idea is that under Gates's funding and direction, Oxitec genetically engineered the virus, then genetically engineered mosquitoes to carry it, and released them in Brazil.  Since then, they (and the virus) have been spreading north rapidly.

My question is: why would Bill Gates do this, given that if the population of the Earth crashes, there will be far fewer people around to purchase updates to Windows every six weeks?  He doesn't really seem to have a lot to gain by spawning a pandemic.  And as for the conspiracy theorists, they're not really clear about this.  The upshot is, "Mwa ha ha ha ha ha ha ha, that's why."

Aedes aegypti [image courtesy of the Center for Disease Control and the Wikimedia Commons]

The problem, of course, is that the whole claim is based in a bunch of falsehoods.  As Christie Wilcox points out in her wonderful blog Science Sushi, Zika is nothing new; it was first isolated and described in 1947 from mosquitoes collected in the Zika Forest of Uganda.  Thus the name.  It spread across Africa by 1968, made a jump to Micronesia in 2007, to Polynesia in 2013, and was first spotted in the Americas -- in Chile, not Brazil -- in 2014.  The genetically modified mosquitoes were developed to combat mosquito outbreaks, not foster them; the GM mosquitoes contain a "kill switch," a set of genes that allows them to mate but results in non-viable offspring.  And because the species of mosquito that carries Zika -- Aedes aegypti -- also carries dengue fever, chikungunya, yellow fever, and malaria, it's hard to imagine how this could be a bad thing, especially considering that the other option is the use of highly toxic pesticides.

But the conspiracy silliness doesn't end there.  Jon Rappoport, whose dubiously sane pronouncements have been featured in Skeptophilia before, has come up with something even goofier.  In his blog post "Zika Hoax: Five Things That Will Happen Next," we hear that there is no connection between Zika and microcephaly (which, of course, could turn out to be true; as I mentioned earlier, scientists are still investigating the point).  Then, however, he runs right off the cliff, predicting that researchers will develop a vaccine for Zika, but that the vaccine and the virus will turn out to be "weaponized biowar [agents]."

Because if you've launched a biological warfare virus, the first thing you'd do is to come up with a vaccine that's also for biological warfare.  And somehow, Zika is both a hoax and an evil biological weapon at the same time.

How evil can you get?  Cf. "Mwa ha ha ha ha ha ha ha ha ha."

Of course, the major problem with all of this foolishness is that the basis of the conspiracy is that the release of the GM mosquitoes coincides, both in time and place, with the outbreak.  And this turns out to be false.  As Wilcox writes:

The epicenter of the outbreak and the release clearly don’t line up—the epicenter is on the coast rather than inland where the map points. Furthermore, the first confirmed cases weren’t reported in that area, but in the town of Camaçari, Bahia, which is—unsurprisingly—on the coast and several hundred kilometers from the release site indicated. 

But perhaps more importantly, the location on the map isn’t where the mosquitoes were released. That map points to Juazeiro de Norte, Ceará, which is a solid 300 km away from Juazeiro, Bahia—the actual site of the mosquito trial. That location is even more on the edge of the Zika-affected area.

On the other hand, think about it; it makes sense that they'd release the GM mosquitoes near where the outbreaks occurred.  Since the whole idea is to control Zika in Brazil, it wouldn't make much sense to release the mosquitoes in, say, Greenland.

But that sort of logic never seems to appeal as much as fact-free and panic-stricken shouting, for some reason.

In any case, bottom line: Zika isn't genetically engineered, isn't new, and isn't being spread by GM super-mosquitoes because of some obscure plot by Bill Gates.  I'd be much obliged if people would stop spreading this nonsense around, because it's got to be annoying to the scientists who are working on the real problem that Zika represents.  Thank you.