The broad‐leaf herbicide 2,4‐dichlorophenoxyacetic acid turns rice into a living trap for a major insect pest and a parasitic wasp

Summary• Synthetic chemical elicitors of plant defense have been touted as a powerful means for sustainable crop protection. Yet, they have never been successfully applied to control insect pests in the field. • We developed a high‐throughput chemical genetics screening system based on a herbivore‐induced linalool synthase promoter fused to a β‐glucuronidase (GUS) reporter construct to test synthetic compounds for their potential to induce rice defenses. • We identified 2,4‐dichlorophenoxyacetic acid (2,4‐D), an auxin homolog and widely used herbicide in monocotyledonous crops, as a potent elicitor of rice defenses. Low doses of 2,4‐D induced a strong defensive reaction upstream of the jasmonic acid and ethylene pathways, resulting in a marked increase in trypsin proteinase inhibitor activity and volatile production. Induced plants were more resistant to the striped stem borer Chilo suppressalis , but became highly attractive to the brown planthopper Nilaparvata lugens and its main egg parasitoid Anagrus nilaparvatae . In a field experiment, 2,4‐D application turned rice plants into living traps for N. lugens by attracting parasitoids. • Our findings demonstrate the potential of auxin homologs as defensive signals and show the potential of the herbicide to turn rice into a selective catch crop for an economically important pest.