How Soil Bacteria Help Plants Call Wasps to Fight Pests

A study published on May 27 in Science Advances found that bean plants under attack by caterpillars release chemical signals into the air to attract predatory wasps as a defense mechanism, a process governed by a single protein named INR (newsbreak.com, wsiu.org). This interaction highlights a complex chemical counterattack used by plants to protect their health against destructive herbivores (newsbreak.com, wsiu.org).

How Bean Plants Deploy Chemical Defenses Against Pests

When caterpillars munch on the leaves of bean plants, compounds in the caterpillar spit trigger the plants to release airborne chemical distress signals (wsiu.org). Adam Steinbrenner, a plant biologist at the University of Washington and one of the study’s authors, noted that these released chemicals are known attractants for parasitoid and predatory wasps (wsiu.org). Some of these wasps eat the caterpillars directly, while others lay their eggs inside the caterpillars’ bodies so the larvae can consume them from the inside out, effectively removing the threat to the bean crop (wsiu.org).

This defensive signaling relies specifically on caterpillar saliva rather than general physical damage (wsiu.org). According to reporting from NPR’s Short Wave podcast, mechanical injury such as cutting a leaf does not prompt the same wasp-attracting response (wsiu.org). While plants constantly release odors in response to wounding—such as the scent of freshly cut grass—the targeted recruitment of aerial reinforcements depends entirely on the biochemical recognition of the feeding pest (wsiu.org).

The Role of the INR Protein in Pest Resistance

To test the protein’s function, researchers grew bean plants featuring naturally occurring mutations in the INR gene alongside plants with functional INR in an experimental field located in Oaxaca, Mexico (newsbreak.com).

The gene knock-out plants failed to emit the defensive gases and attracted significantly fewer wasps than their functional counterparts (newsbreak.com). This outcome provides direct empirical support for a previous study by the same research team that first identified the biochemical pathway underlying the defense mechanism (newsbreak.com).

Implications for Companion Planting and Agriculture

The findings illustrate how the localized actions of a single protein can alter insect behavior and safeguard plant health (newsbreak.com). Furthermore, researchers point out that these defensive emissions could extend benefits to neighboring vegetation in agricultural settings (newsbreak.com).

Farmers frequently grow beans alongside companion crops like corn, relying on the mutual benefits each species provides (newsbreak.com). While beans naturally enrich the soil for neighboring plants, the action of the INR protein suggests that companion crops might also gain direct pest protection from nearby bean plants under attack (newsbreak.com).