New Scientist reports on research at the Federal University of Pelotas in Brazil, where Gabriela Niemeyer Reissig and colleagues have found that tomatoes being eaten by insects send electrical warning signals to the rest of the plant:
They studied small cherry tomato plants (tomatoes are a fruit, botanically speaking) by placing them inside Faraday cages, which block external electric fields, and confined caterpillars of the moth Helicoverpa armigera on the surface of fruit within plastic bags.
Electrodes placed in the fruit stalks showed that the patterns of electrical activity changed during and after the caterpillars started eating. They also varied depending on whether the fruits were ripe or green. “The electrical activity of the fruit is constantly changing every second,” says Niemeyer Reissig. “We can find a [distinct] pattern in the electrical activity when an insect attacks.”
There was also a rise in levels of hydrogen peroxide produced by untouched fruit and leaves all over an attacked plant.
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You can read their research here, in Frontiers in Sustainable Food Systems.