Isovaleronitrile co-induced with its precursor, l-leucine, by herbivory in the common evening primrose stimulates foraging behavior of the predatory blue shield bug

<p>Herbivore-induced plant volatiles play important roles in plant–insect and plant–plant interactions. The common evening primrose, <i>Oenothera biennis</i>, is often infested by the flea beetle, <i>Altica oleracea</i>, on which the predatory blue shield bug, <i>Zicrona caerulea</i>, is usually found. This observation suggests that the predatory bug can discriminate infested plants from intact ones to locate its prey. In this study, l-leucine-derived nitrogen-containing compounds [isovaleronitrile (3-methylbutanenitrile), (<i>E</i>/<i>Z</i>)-isovaleraldoxime and 3-methyl-1-nitrobutane] and some terpenes were identified as a characteristic volatile blend from herbivore-infested <i>O</i>. <i>biennis</i> leaves by gas chromatography/mass spectrometry, chemical synthesis, and incorporation assays using deuterium-labeled l-leucine. Volatile emission was also elicited by exogenous methyl jasmonate (MeJA), but not by mechanical damage. l-Leucine accumulated temporarily in <i>O</i>. <i>biennis</i> leaves after MeJA treatment prior to isovaleronitrile emission. Behavioral assays revealed that <i>Z</i>. <i>caerulea</i> showed a strong preference for herbivore-infested leaves, their volatiles, and isovaleronitrile in laboratory conditions.</p> <p>Herbivore-induced volatiles, including l-Leu-derived isovaleronitrile, from Oenothera biennis leaves elicit foraging behavior of a predator, Zicrona caerulea.</p