Got Herbivores? Turn Them Into Cannibals!

Plants have to deal with quite a lot in their day to day lives. They can't get up and move like animals can. Due to their sessile nature, plants rely on a suite of physical and chemical traits for defense. The world of plant chemistry is quite amazing and thanks to new research published in Nature Ecology & Evolution, it has gotten even more interesting. Under attack by herbivorous insects, some plant species are able to turn their vegetarian predators into cannibals. 

Cannibalism in insects is not unheard of, even among the herbivorous species. When the going gets tough, why not eat your sibling or your neighbor? Well, research using tomatoes and the army beetworm (Spodoptera exigua) suggests that plants might be able to induce this behavior in caterpillars long before it would happen naturally. It makes sense too. Plants that are able to induce cannibalistic behavior via chemical means not only reduce grazing pressures on their own tissues, they also reduce the number of herbivores in the system.

The chemical in question here is called methyl jasmonate. It is a volatile organic compound produced by a plethora of plant species and is thought to play in role in a diverse array of biological functions such as germination, root growth, fruit ripening, and defense. It is often released when a plant becomes damaged. Neighboring plants are able to pick up on this compound and will begin to beef up their own defenses in response. After all, if your neighbor is being attacked, there is a decent chance you will be too. 

Researchers investigating the effects of this chemical on the beetworm (a common aggricultural pest) found that plants that were treated with methyl jasmonate induced beetworms to turn on one another through cannibalism. Caterpillars hanging out on plants that were not treated with methyl jasmonate only turned to cannibalism after they had consumed all of the leaves available, if at all. 

The researchers are now gearing up to figure out whether inducing cannibalism also helps to spread disease among caterpillars. This exciting new form of plant defenses opens up doors to many new questions and potentially safer forms of pest control. Considering the near ubiquity of methyl jasmonate in the botanical world, it begs the question as to how common this form of defense really is. 

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