<i>Megalurothrips usitatus</i> Feeding-Induced <i>De Novo</i> Synthesis of the C8 Volatiles 1-Octen-3-ol and 2-Ethyl-1-hexanol in Cowpea Plants Regulates Plant–Herbivore–Predator Interactions

Analyzing the role of herbivore-induced volatiles in plant-herbivore-natural enemy interactions is crucial for developing integrated pest management strategies. This study identified 1-octen-3-ol and 2-ethyl-1-hexanol as the primary C8 volatiles induced by <i>Megalurothrips usitatus</i> infestation in cowpea flowers. The concurrent accumulation of glycosides of these volatiles, along with the upregulation of <i>LOX</i> and <i>HPL</i> expression, suggested that the increased emissions of 1-octen-3-ol and 2-ethyl-1-hexanol result from enhanced <i>de novo</i> biosynthesis regulated by herbivore-induced jasmonate. 1-Octen-3-ol exhibited strong repellent effects against <i>M. usitatus</i> and attracted its natural enemy, <i>Orius similis</i>, at low concentrations. By contrast, 2-ethyl-1-hexanol repelled <i>M. usitatus</i> but did not exert a significant attractant effect on <i>O. similis</i>. These volatiles prime the defense mechanism in cowpea plants against <i>M. usitatus</i>, which highlight their promising role in controlling thirp populations and enhancing cowpea cultivation.