Sunday, July 16, 2017

Plants Have Evolved To Make Caterpillars Cannibalize Themselves

True Activist | Jul 15, 2017 | Amelia Kinney

These plants are turning caterpillars against each other.

Credit: Pixabay
Typically, we see caterpillars climbing all over plants, munching on leaves. It seems that some plant species have now developed a new creepy defense method to contend with these predators.

A recent study published in Nature: Ecology & Evolution, titled “Induced defences in plants reduce herbivory by increasing cannibalism” shows certain tomato plants — Solanum lycopersicum — can produce a defensive chemical, inducing beet armyworms to devour each other.

According to the article, “Plants are not passive bystanders in their interactions with herbivores: plants alter their chemistry, morphology and other components of their phenotype to reduce herbivory, often using cues from their environment to initiate these defences before any actual attack occurs.”
The study, guided by Dr. John Orrock from the Department of Integrative Biology at the University of Wisconsin in Madison, exposed tomato plants to different amounts of methyl jasmonate (MeJA) — an airborne chemical released by plants to alert each other of approaching pests. Scientists found that when cued by MeJA, tomato plants produced distinct toxins, making themselves less nutritious to insects.

Dr. Orrock and his team tested whether a response was triggered in plants to incite cannibalism in caterpillars. They interlaced tomato plants with MeJA, and fed leaves from both interlaced and control plants to caterpillars. Results showed “plants that were strongly induced before exposure to generalist insect herbivores (Spodoptera exigua) caused herbivores to begin consuming each other earlier, leading to increase average rates of cannibalism.”

Beet armyworm. Credit: UGA
The study also refers to the benefits this defense provides for plants. “Like predation and parasitism, cannibalism reduces herbivory by increasing herbivore mortality. However, unlike predation and parasitism, cannibalism also benefits plants because herbivores that exhibit cannibalism also stop consuming as much plant biomass.”

However, professor Orrock also warns about the cost this system can eventually cause to the plants. “It is very possible that the plants will strike a balance and decide if the attack is serious enough to activate the defences”. Because of this, he explains timing is critical, “if plants can induce pests to eat each other earlier, there will be more of the plant left untouched.”

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