Inducible defences, chemical aposematism and the spatial ecology of plant–herbivore interactions in tall goldenrod, Solidago altissima L.

Abstract Plants can respond to herbivore attack by inducing resistance traits that affect subsequent herbivore performance and behaviour. Here, we investigate how such induced responses in Solidago altissima L. (tall goldenrod) function to spread herbivore damage more evenly across plant populations, thereby reducing the amount of herbivory for each individual plant. In field and laboratory experiments with Trirhabda virgata J. L. LeConte (1865) beetle larvae, we demonstrate that herbivory induces strong resistance in S. altissima , resulting in reduced larval growth and behavioural avoidance of previously damaged plants. Volatile organic compounds (VOCs) emitted from damaged plants serve as olfactory cues for larval decision‐making, suggesting a form of chemical aposematism informing the beetles' movement through the plant population. Beetle larvae use these cues to move away from damaged plants and preferentially colonize undamaged neighbours, particularly when plants are connected by overlapping foliage. Isolated plants, by contrast, experience significantly more damage due to reduced larval emigration. With seasonal surveys, we found a shift from clumped to a more even herbivore distribution, driven by plant‐induced resistance and VOC signalling. These results support a ‘risk‐spreading’ function of inducible resistance, contingent on herbivore mobility and plant connectivity, and offer an alternative ecological framework for the evolution of inducible plant defence traits beyond traditional cost‐saving hypotheses. This research underscores the role of plant chemical signalling and spatial structure in shaping herbivore–plant interactions and community dynamics. Read the free Plain Language Summary for this article on the Journal blog.