Insects sense danger on mammals' breath

August 9, 2010

When plant-eating mammals such as goats chomp on a sprig of alfalfa, they could easily gobble up some extra protein in the form of insects that happen to get in their way. But a new report in the August 10th issue of Current Biology, a Cell Press publication, shows that plant-dwelling pea aphids have a strategy designed to help them avoid that dismal fate: The insects sense mammalian breath and simply drop to the ground.

"Tiny insects like aphids are not helpless when facing large animals that rapidly consume the plants they live on," said Moshe Inbar of the University of Haifa in Israel. "They reliably detect the danger and escape on time."

Inbar said he had always wondered about accidental predation of small plant-dwellers based on his observations of insects that don't really move around. "As soon as we started to work on this problem, we suspected that the aphids responded to our own breath," he said. (The researchers later used snorkels to keep their own breath from mucking up their experiments).

The researchers allowed a goat to feed on potted alfalfa plants infested with aphids. "Strikingly, 65 percent of the aphids in the colonies dropped to the ground right before they would have been eaten along with the plant," the researchers write.

That mass dropping might have been triggered by many cues: plant shaking, sudden shadowing, or the plant-eater's breath. While a quarter of the aphids dropped when plants were shaken, more than half fell to the ground in response to a lamb's breath, the researchers report.

Shadows had no effect on the aphids' dropping behavior. Ladybugs, an insect enemy of aphids, didn't inspire that kind of synchronous response either.

Further studies with an artificial breath apparatus allowed the researchers to test what it was about the breath that tipped the aphids off. It turned out it wasn't or other known chemical ingredients found on mammalian breath. Only when the controlled airstream was both warm and humid did it lead to impressive dropping rates of 87 percent in a room with otherwise low humidity.

Inbar said that the aphids' "elegant solution" to the problem of incidental predation is likely practiced by other species as well.

"This remarkable response to mammalian-specific cues, in spite of the inherent cost of an aphid's dropping off the plant, points to the significance of mammalian herbivory to plant-dwelling ," the researchers concluded. "We predict that this sort of escape behavior in response to mammalian breath may be found among other invertebrates that live on plants and face the same threat."

Explore further: Aphids make 'chemical weapons' to fight off killer ladybirds

More information: Inbar et al.: “Mammalian herbivore breath alerts aphids to flee host plant.” Publishing in Current Biology, August 10, 2010. www.current-biology.com.

Related Stories

Transgenic maize is more susceptible to aphids

August 29, 2007

The environmental consequences of transgenic crops are the focus of numerous investigations, such as the one published in the journal PloS ONE, which was carried out by Cristina Faria and her colleagues, under the supervision ...

Virus pulls bait and switch on insect vectors

February 1, 2010

A common plant virus lures aphids to infected plants by making the plants more attractive, but when the insects taste the plant, they quickly leave for tastier, healthier ones. In the process, the insects rapidly transmit ...

Recommended for you

How bees naturally vaccinate their babies

July 31, 2015

When it comes to vaccinating their babies, bees don't have a choice—they naturally immunize their offspring against specific diseases found in their environments. And now for the first time, scientists have discovered how ...

Researchers design first artificial ribosome

July 29, 2015

Researchers at the University of Illinois at Chicago and Northwestern University have engineered a tethered ribosome that works nearly as well as the authentic cellular component, or organelle, that produces all the proteins ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.