Insects can sense danger on mammals’ breath

WASHINGTON - Plant-eating mammals could easily gobble up some extra protein in the form of insects that happen to get in their way when they munch on plants. But insects have a strategy to help them avoid that dismal fate, a new study shows.

Insects can sense mammalian breath and simply drop to the ground, ScienceDaily said quoting a report in the latest issue of Current Biology.

“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 wrote.

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 the lamb’s breath, they said.

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 carbon dioxide 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.