Effects of herbivore damage and nutrient level on induction of iridoid glycosides in Plantago lanceolata

Abstract

Damage by larvae of the buckeye butterfly (Junonia coenia) resulted in removal of 15–25% of Plantago lanceolata leaf area. Plants grown under high nutrients were larger than those grown under low nutrients. Twenty-eight days after herbivory, plants grown under high nutrients were still larger than those grown under low nutrients, and plants exposed to herbivores were significantly smaller than those not exposed to herbivores, regardless of the nutrient treatment. Damage by larvae also increased the iridoid glycoside content in the leaves and reproductive tissues of these Plantago lanceolata relative to undamaged controls. Whether damaged or undamaged, the iridoid glycoside content of P. lanceolata was highest in the reproductive tissues and lowest in the roots. Although initial concentrations of iridoid glycosides were significantly higher in plants grown under low nutrient conditions than in plants grown under high nutrient conditions, nutrient availability did not alter the phytochemical response of plants to herbivore damage. These results provide additional support for the defensive role of the iridoid glycosides in Plantago lanceolata by demonstrating that phytochemical variation is not always an incidental effect of nutrient stress but can be a direct response to damage by herbivores.