I have a soft spot for interesting biological security measures, especially by plants. I’ve used them as examples in several of my books. Here’s a new one: when tomato plants are attacked by caterpillars, they release a chemical that turns the caterpillars on each other:
It’s common for caterpillars to eat each other when they’re stressed out by the lack of food. (We’ve all been there.) But why would they start eating each other when the plant food is right in front of them? Answer: because of devious behavior control by plants.
When plants are attacked (read: eaten) they make themselves more toxic by activating a chemical called methyl jasmonate. Scientists sprayed tomato plants with methyl jasmonate to kick off these responses, then unleashed caterpillars on them.
Compared to an untreated plant, a high-dose plant had five times as much plant left behind because the caterpillars were turning on each other instead. The caterpillars on a treated tomato plant ate twice as many other caterpillars than the ones on a control plant.
from Tomato-Plant Security