Megalurothrips usitatus Feeding-Induced De Novo 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 Megalurothrips usitatus infestation in cowpea flowers. The concurrent accumulation of glycosides of these volatiles, along with the upregulation of LOX and HPL expression, suggested that the increased emissions of 1-octen-3-ol and 2-ethyl-1-hexanol result from enhanced de novo biosynthesis regulated by herbivore-induced jasmonate. 1-Octen-3-ol exhibited strong repellent effects against M. usitatus and attracted its natural enemy, Orius similis, at low concentrations. By contrast, 2-ethyl-1-hexanol repelled M. usitatus but did not exert a significant attractant effect on O. similis. These volatiles prime the defense mechanism in cowpea plants against M. usitatus, which highlight their promising role in controlling thirp populations and enhancing cowpea cultivation.