Plants Turn Caterpillars into Cannibals

Chemical produced by tomato plants in response to pest attack can change insect behavior

It is not unusual for insect pests to feast on each other as well as on their staple veg, but it's now been shown that tomato plants can team up to directly push caterpillars into cannibalism.
“This is a new ecological mechanism of induced resistance that effectively changes the behaviour of the insects,” says Richard Karban, who studies interactions between herbivores and their host plants at the University of California at Davis and was not involved in the study.
Herbivorous pests often turn on each other when their food is of poor quality or it runs out. And some plants are known to affect the behaviour of their pests by making them more predatory towards other species. But until now it was unclear whether plants could directly cause caterpillar cannibalism.
Integrative biologist John Orrock and his colleagues at the University of Wisconsin in Madison triggered a defensive reaction in tomato plants (Solanum lycopersicum) by exposing them to various amounts of methyl jasmonate (MeJA). This is an airborne chemical that plants release to alert each other to danger from pests. When cued with MeJA, tomato plants respond by producing toxins that make them less nutritious to insects.
The researchers then allowed caterpillars of a common pest, the small mottled willow moth (Spodoptera exigua), to attack the crop. Eight days later, they observed that plants more strongly cued with MeJA had lost less biomass compared with control plants or with ones that had received a weaker induction. This showed that the reaction was somehow effective at protecting the plants.