How bean plants call on wasps for help when hungry caterpillars attack

Some plants are not the sitting ducks they appear to be when they come under attack. If a hungry caterpillar starts to chomp on the succulent leaves of a common bean plant, a highly sophisticated defense system kicks into ...

A team led by scientists from the University of Washington made the discovery after conducting a series of laboratory and field experiments in Mexico. Their paper details the chain of events that unfold from the moment a caterpillar starts feeding. As the insect eats, fragments of plant proteins are broken down in its gut, leading to the formation of inceptin , a small peptide. The caterpillar then deposits this molecule back on the leaf through its oral secretions.

Alarm system A sensor on the surface of the leaf called the inceptin receptor (INR) recognizes the molecular signature of inceptin even at low concentrations. This triggers the plant to release volatile chemicals into the air, attracting nearby predatory wasps. Over millions of years of evolution, the stinging insects have learned to associate these airborne chemicals with a food source, and they swoop in to take the caterpillars out. The researchers uncovered this by growing bean plants in pairs. In each pair, one plant carried a mutation that disabled the inceptin receptor.

Bean plants (Phaseolus vulgaris) in the field in the state of Oaxaca, Mexico. When treated with caterpillar elicitor peptides, plants can induce indirect defenses by attracting beneficial insects, predatory wasps in the genus Polybia and Mischocyttarus. Plants lacking the Inceptin Receptor gene fail to emit inducible volatiles and attract fewer wasps, connecting plant immune recognition to the efficacy of their indirect defenses against herbivorous pests. Credit: Brian Behnken Read more

Credit: Brian Behnken Read more