Hot and heavy: Insects sense the breath of approaching herbivores and flee plants

By Nicholette Zeliadt

Plant-dwelling insects are in perpetual danger of being accidentally munched on by plant-eating animals. One such insect, the sap-sucking aphid (a common pest in gardens), has an effective escape plan, though: the bugs detect an approaching herbivore’s breath and simply drop off the plant before it’s eaten.

Researchers at the University of Haifa at Oranim, Israel first noticed this phenomenon when they allowed a goat to feed on aphid-infested alfalfa plants—65 percent of the plant pests simultaneously dropped to the ground just before the vegetation was devoured.

The team suspected that several cues might have motivated the mass dropping, including the sudden shadow cast by the goat, plant-shaking triggered by the munching marauder and/or the herbivore’s exhalations. The researchers tested the effects of each cue individually and found that simply casting a shadow on the plants had no effect on the aphids. Vibrations caused by leaf picking caused only one quarter of the insects to flee the plant. By contrast, when the researchers placed a lamb within five centimeters of the foliage (close enough to breathe on it, but not nibble on it), nearly 60 percent of the bugs dropped to the floor, suggesting that breath was the key danger signal… Read More>>

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