Plants produce a bewildering diversity of defensive compounds against their herbivore attackers. In addition to permanently expressed (constitutive) chemical defenses, plants generally show an array of inducible defenses which are only formed when the plant is under attack. However, there is increasing evidence that inducible defenses may persist on a long-term time scale, and across generations. Nevertheless, transgenerational studies quantifying multiple plant traits and their impact on plant survival in nature are lacking. In this study, we show for the first time, transgenerationally elevated cyanogenesis (release of hydrogen cyanide from cyanogenic precursors) in wild lima bean plants, Phaseolus lunatus, experimentally exposed to damage by natural chrysomelid herbivores, Gynandrobrotica guerreroensis. First generation offspring from damaged parents showed higher β-glucosidase activity, released more cyanide and showed significantly lower mortality compared to plants grown from seeds collected from non-manipulated, less damaged parent plants. However, this effect was significant only at the seedling stage of the first offspring generation and within this generation vanished within 4 weeks, indicating a transient nature of transgenerationally enhanced defense. While defense traits remained at elevated levels only for a relatively short period of time, our study shows the importance of a transgenerational inherited defense for seedling survival in nature.