A new study has shown that under certain circumstances, tomatoes can induce cannibalism in certain types of insects, such as caterpillars.

For the most part, we don't really think about the impact that plants have on their environment. We understand that they are necessary for food and the production of oxygen, but beyond that, we tend to think of them as passive actors — with some exceptions. Despite this misconception, it is a fact that plants can impact their environment in more direct ways, and one of the most interesting is the fact that tomatoes can induce cannibalism in caterpillars.

When tomato leaves are eaten by herbivores, such as caterpillars, they will send out a signal that warns their fellow tomato plants of what is happening. This signal causes the other plants to release a chemical, which gives their leaves a particularly foul taste that helps ward off predators. While attempting to simulate these conditions in a laboratory, researchers found that when enough of these chemicals were applied to plants, caterpillars resorted to cannibalism.

The Experiment

The experiment was carried out by Professor John Orrock and two of his research assistants. The researchers used four batches of tomato plants. One was a control group and the other three were sprayed with varying levels of the chemical methyl jasmonate in doses of low, medium, or high. They also added at eight caterpillars into each of the containers.

What they found was that the plants with the highest dosage of methyl jasmonate were mostly intact, and the caterpillars turned to cannibalism quicker than their counterparts who had access to less-contaminated plants. As it turns out, there is a point where the plants taste bad enough that the insects preferred devouring their own.

When the tomato plants were eaten, the other insects turned to cannibalism as well, but not as quick as the ones that were sprayed with high doses of methyl jasmonate.

"Not only do these guys become predators, which is a victory for the plant, they are getting a lot of food by eating one another," says Orrock. "We struck upon a way that plants defend themselves that nobody had really appreciated before."

Orrock noted that, overall, this was a major asset for the plants since it protected them from being eaten and provided an alternative food source for the caterpillars.

"From the plant's perspective, this is a pretty sweet outcome, turning herbivores on each other," Orrock says. "Cannibals not only benefit the plant by eating herbivores, but cannibals also don't have as much appetite for plant material, presumably because they're already full from eating other caterpillars."

In nature, tomato plants don't produce quite the amount of methyl jasmonate that was used on some of the laboratory plants, so cannibalism remains a rare outcome for caterpillars living in the wild.

The study was published in Nature Ecology & Evolution.