Plants Can Turn Caterpillars Into Cannibals: How Induced Pest Cannibalism Benefits Plants


Plants may appear helpless from being eaten by herbivorous pests but findings of a new study have revealed a special defense mechanism that plants employ to protect themselves from leaf-munching organisms like caterpillars.

Turning Hungry Pests Into Cannibals

This defense mechanism can turn caterpillars into cannibals that eat each other. Plants deploy special chemicals to make their foliage less appetizing, which can result in caterpillars munching on each other instead.

Herbivorous pests are known to turn to each other when their food runs out or is of poor quality. Now, a research published in the Nature Ecology & Evolution journal sheds light on how plants trigger caterpillar cannibalism.

Study researcher John Orrock, of the University of Wisconsin-Madison, and colleagues found that when hungry herbivores attack plants, the latter leak chemicals that can make them foul-tasting to caterpillars. The less appetizing leaves then prompt the pests to eat each other.

"Plants can defend themselves so much that they food-stress the herbivore, and then the herbivores determine that rather than have plants on their menu, they should have caterpillars at the top of their menu," Orrock said.

Chemical Can Turn Caterpillars Into Cannibals

The researchers sprayed tomato plants with a substance that plants produce as a response to environmental stress, to set off their defense mechanism.

The chemical, known as methyl jasmonate, allowed plants to change their chemistry causing them to be less appetizing to beet armyworm caterpillars that the researchers placed on treated plants.

Eight days after allowing the caterpillars to attack the crops, the researchers observed that the plants that were more strongly cured with methyl jasmonate lost less biomass compared with the untreated plants and those that had lesser amounts of methyl jasmonate.

The phenomenon has already been documented in other plants. Research also suggests that plants can actually sense when the plants surrounding them are being attacked, which prompts the production of the methyl jasmonate by the other plants.

Caterpillar Cannibalism Benefits Plants

The researchers fed leaves of treated and nontreated plants to caterpillars and found that the caterpillars that were fed with leaves from the treated plants turned to dead caterpillars in the containers and ate more of them compared with those that were fed with leaves from the controlled plants.

Researchers said that this particular defense mechanism of plants offers advantages, one of which is controlling the population of pests that are harmful to plants.

"We found that defenses that promote cannibalism benefit tomatoes in two ways: cannibalism directly reduces herbivore abundance, and cannibals eat significantly less plant material," the researchers wrote in their study. "This previously unknown means of defense may alter plant-herbivore dynamics, plant evolution and pathogen transmission."

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