Ever lit a citronella candle to ward off mosquitoes, only to have 'em appear in droves? Well, believe it or not, you may have actually been attracting the bugs. Because while high concentrations of those pine-and-lemon-scented chemicals might repel mosquitoes, at low concentrations they lure the bloodsuckers in.
Audrey Odom, who studies mosquitoes at Washington University, calls it the "Chanel hypothesis." Too much perfume is awful, but a little is pretty nice. Plants take advantage of that to advertise their nectar—because no, mosquitoes don't live on blood alone.
But here's where things get weird. Plasmodium—the malaria parasite—also manufactures those alluring odor molecules, called terpenes. It does so using a chloroplast-like organelle, like the one plants use to capture sunlight. The malaria parasite's version can't trap light, but it can still manufacture plant perfume. The study appears in the journal mBio. [Megan Kelly et al, Malaria Parasites Produce Volatile Mosquito Attractants]
The parasites produce these scents in the lab, and mosquitoes are attracted to them. The only question left for Odom and her colleagues is whether these chemicals also appear in the breath of infected humans. If they do, she says, the goal is to build a quick breathalyzer test for malaria, instead of the blood test used today—which would attract doctors to a patient in need before the next mosquito comes to bite.
[The above text is a transcript of this podcast.]