Isoprene emissions influence herbivore feeding decisions

<jats:title>ABSTRACT</jats:title><jats:p>Isoprene (C<jats:sub>5</jats:sub>H<jats:sub>8</jats:sub>, 2‐methyl 1,3‐butadiene) is synthesized and emitted by many, but not all, plants. Unlike other related volatile organic compounds (monoterpenes and sesquiterpenes), isoprene has not been shown to mediate plant–herbivore interactions. Here, for the first time, we show, in feeding choice tests using isoprene‐emitting transgenic tobacco plants (<jats:italic>Nicotiana tabacum</jats:italic> cv. Samsun) and non‐emitting azygous control plants, that isoprene deters <jats:italic>Manduca sexta</jats:italic> caterpillars from feeding. This avoidance behaviour was confirmed using an artificial (isoprene‐emitting and non‐emitting control) diet. Both <jats:italic>in vivo</jats:italic> and <jats:italic>in vitro</jats:italic> experiments showed that isoprene can activate feeding avoidance behaviour in this system with a dose–response effect on caterpillar behaviour and an isoprene emission threshold level of &lt;6 nmol m<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup>.</jats:p>