Scientists from the U.S. department of Agriculture have discovered how The Aedes aegypti mosquito detects the chemical structure of a compound called octenol as one way to find a mammalian host for a blood meal.

Scientists have long known that mosquitoes can detect octenol, but this most recent finding, published in PLoS One, explains in greater detail how Ae. aegypti--and possibly other mosquito species--detect the compound.

Ae. aegypti, according to the study, taps into the "right-handed" and "left-handed" structural nature of octenol, which is emitted by people, cattle and other mammals. This ability to detect the "handedness" of molecules has been shown in mammals, but the discovery is the first case of scientists finding out how it works in an insect.

When they hunt for a blood meal, mosquitoes hone in on a variety of chemicals, including carbon dioxide, lactic acid, ammonia and octenol. Octenol is one of many carbon-based compounds that have a molecular structure that can take on either a "right-handed" or "left-handed" form. Each form is a mirror image of the other, and a form's "handedness" is determined by how its molecular bonds are assembled.

The scientists used frog eggs to help them make their discovery. They injected RNA from Ae. aegypti into the frog eggs, allowing the egg membranes to mimic the mosquito's ability to detect octenol. Then they attached microelectrodes to the frog egg cell membranes, passed octenol over them and recorded the electrical signals stimulated by the odors.

Tests using both the right- and left-handed forms of octenol found heightened electrical activity when the membrane was exposed to the right-handed form, and weakened activity when it was exposed to the left-handed form.

There are many natural compounds that can take on either a right-handed or left-handed form. While the effects of those differences on many plants and animals remains a mystery, the report shows the effects of octenol's dual structure on the yellow fever mosquito and adds to scientists' understanding of how mosquitoes sense the world around them. It also may open the door to speedier development of better mosquito repellents and traps, according to Dickens.

JD Bohbot, JC Dickens, 'Characterization of an Enantioselective Odorant Receptor in the Yellow Fever Mosquito Aedes aegypti, PLoS ONE, September 2009, 4(9): e7032; doi:10.1371/journal.pone.0007032