The effect of elevated UV‐B radiation on herbivory of pea by <i>Autographa gamma</i>

Abstract

Abstract Leaves exposed to above‐ambient fluxes of ultraviolet‐B (UV‐B) radiation commonly contain increased concentrations of phenolic compounds which may influence herbivores. However, the hypothesis that elevated UV‐B modifies herbivory, whether mediated by phenolics or other plant constituents, has rarely been studied experimentally. We investigated the responses of the moth Autographa gamma L. (Lepidoptera: Noctuidae) to pea ( Pisum sativum L.) grown at a range of plant‐effective UV‐B fluxes. Although total phenolics did increase significantly with increasing UV‐B, this change had little deleterious effect on the 5th instar larvae of A. gamma. However, tissue nitrogen also increased with increasing UV‐B. Increased nitrogen was correlated with an increase in the efficiency with which larvae utilized their food and in larval growth rate, but in a reduction in the amount of plant material consumed. The apparently major role of nitrogen in determining herbivore responses to changing UV‐B demonstrates the risks in predicting such responses soley on the basis of changes in phenolics and other secondary metabolites.