Engineering challenge: build a mosquito-sized robot whose sensors find biteable humans by (a) carbon dioxide they exhale, (b) body heat and (c) various odors from their skin.
For over 20 years, scientists have tried to learn how mosquitoes’ sensors work, and why DEET (a powerful repellent) defeats them.
Now, they know – or at least they know a little. The answer is in molecular receptors on sensory nerve cells (which are on the insects’ antennae.) (“Receptors,” recall, are long crinkled — so to speak – molecules. Parts of them protrude from a cell. Other molecules latch onto their intricate shapes, like keys into locks. This signals the cell.)
Molecules of odors (sweat, for instance) or carbon dioxide lock onto those receptors on the antennae. The receptor molecule then writhes to a different shape in thousandths of a second. It is a long molecule; one part dangles (so to speak) inside the nerve cell. The writhing there triggers chemical machinery. Its result: electrical signals shoot from the antennae into nerve cells that pass for a “brain,” in the mosquito’s head. The insect “knows” that a breathing human, or a sweating one, is near.
So how do DEET’s large molecules mess this up? The answer is that over 60 different receptors respond to sweat or breathing or body heat or various odors. (Mosquitoes bite any animal, and can find them all.) Signals are copious, but the “brain” weaves them into “knowledge.” DEET scrambles the signals to nonsense. It inhibits some sensors, excites others, and does that to different degrees.
It’s as if eyes see ”Warm human at 2 o’clock“, but a DEET-like chemical scrambles perception to “x#$g?& Q$#%^&.” Mosquitoes are baffled too. Bafflement was proven to be DEET’s effect. Researchers also found mutant species whose receptor molecules can’t “lock” with DEET. So DEET doesn’t work on them.
Why is this important? “Importance” and “mosquitoes” may seem a preposterous combination: grant that. But….solving a 20 year old puzzle…well, it deserves notice.
And isn’t it amazing that a mosquito “knows,” using this machinery of 60+ receptors? Then think of trillions of them, emerging from fly-speck-sized eggs, via symphonies of bio-chemicals directed by DNA molecules. An aquatic wriggling larva hatches in about a day. It molts four times in a week or two, then forms a cocoon. An airborne predator soon emerges, armed with these incredible sensory weapons.
M. Pellegrino et al., A natural polymorphism alters odour and DEET sensitivity in an insect odorant receptor, 478 Nature 511-514, 27 October 2011.