Scientists at the University of Washington have discovered how bean plants detect caterpillar feeding and summon parasitic wasps as natural defenders. Led by biologist Adam Steinbrenner, the team identified a specialized immune receptor that recognizes caterpillar saliva, triggering the plant to release chemical signals that attract predatory wasps to attack the invaders.

When caterpillars feed, they regurgitate an 11-amino acid fragment called In11 that comes from the plant's own proteins. Bean plants evolved the inceptin receptor specifically to detect this molecular signature. When activated, the receptor initiates a signaling cascade that causes the plant to emit volatile organic compounds signaling "caterpillar feeding here" to passing wasps.

The researchers found a natural bean mutation with a dysfunctional receptor in a Honduran strain called W6 13807. Through selective breeding, they created sibling plants with identical genetics except for the functional receptor. Lab and field tests in Oaxaca, Mexico showed plants without the receptor suffered 70% more caterpillar damage and failed to summon wasps effectively.

This discovery reveals a sophisticated plant defense system that scientists could potentially enhance to improve crop protection. Understanding how plants detect specific herbivore attacks opens new possibilities for developing crops that can more effectively call in their own natural defenses against pests.