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Tomatoes turn caterpillars into cannibals



July 21, 2017

New research has uncovered a brilliant but unsettling ability that many plants possess – they can release chemical defences that make their soft tissues so inedible to caterpillars that these predators end up opting to eat each other instead!

It’s long been known that plants can release a myriad of compounds to stave off chewing pests and alert nearby plants they’re under attack. But research out of the University of Wisconsin and published in Nature recently has shown that plants can be so effective in this mechanism that they drive predatory herbivores to cannibalism.

Behaviour ecologist, Associate Professor John Orrock, isolated the volatile organic compound responsible for initiating plant defence systems in the lab and applied it to tomatoes being attacked by caterpillars. The compound, methyl jasmonate, is made by most plants in response to biotic and abiotic stresses, be they grazing by insects and other animals or damage by the elements. Methyl jasmonate can be transferred between plants by physical touch as well as wind, which nearby plants sense and use as a head start in manufacturing defensive compounds before they too come under attack.

The study concluded that ‘well-defended’ plants had more biomass at the end of the experiment than less well-defended plants, thanks to inducing cannibalism sooner. A well defended plant is one that is nearby the plant initially attacked, after which it releases methyl jasmonate to warn its surrounding kin that chewing insects are in the area. Plants that have this head start are more effective at inducing cannibalism in pests than the initial host. However, the host can still induce cannibalism, but only once all the leaf material has been consumed.

The implications of this research have promise for the manufacture of pesticides that induce plants’ own in-built defence strategies to reduce damage by chewing, lapping and sucking insects – not just caterpillars.

Next time you see a caterpillar munching away on your plants don’t freak out! Plants have been coping with attacks from all sides for millions of years and have some pretty nifty, albeit horrifying ways of coping with them.



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