Tuesday, March 23, 2010

Come hither

Is there anything more annoying than to wake in the middle of the night to the sound of a mosquito buzzing near one's ear? It is a nightly occurrence on the island of Exuma where I spend the winter. No matter how diligently we try to keep mosquitos out of the house, a few get in on any given day. In the dark of night, they find us in our bed. Then -- that barely audible whirr of wings anticipates the moment when Anopheles plunges her bloodsucking proboscis into our flesh.

How do they find us, all the way at the other end of the house? Unbeknown to us, as we lay in the bed, we emit a cloud of odorants -- indole, phenol, methtlphenols, and other aromatic compounds -- tiny molecules that drift through the house and say "human blood, follow me up-gradient." And Anopheles, as it turns out, has built into her antennae odorant detectors precisely tuned to exactly the odors that humans emit.

In the 4 March issue of Nature, a group of researchers from Yale and Vanderbilt Universities, report a brilliant body of work identifying and analyzing the mosquito' s suite of odorant detectors. Here, for you edification, is just one illustration from the report, showing the "tuning curves" for 36 human odorant molecules. At the top of the chart are the structures of several odorant molecules that generate particularly strong responses. Click to enlarge.

All this (and more) on the mosquito's antennae -- so perfect a match between insect and human that one could almost see the signature of Intelligent Design, except that the chemical matchmaking facilitates the transmission of the malaria parasite, which afflicts hundreds of millions of people each year -- the work of an Intelligent Designer perhaps, but certainly not one who cares about the human species.

No, what we are see here is the infinitely fine tuning of natural selection, acting over eons of time, to provide the female Anopheles mosquito with the human blood she needs to nourish her offspring, and to incidentally facilitate the life cycle of the malaria parasite.

We trust that our Exumian mosquitos are malaria free. Nevertheless, we wake in the night in our house-filling envelope of mosquito attractants, slapping our ears in a vain attempt to keep the little devils from sucking our blood. Dare we hope that with this new research we'll soon be able to buy an air "unfreshener" that will emit a cloud of odrorants more perfectly mimicking the human species than even our own faint emanations, luring the mosquitos to, say, a fatal electrocution.