An insect pheromone primes tolerance of herbivory in goldenrod plants

Environmental cues that predict increased risk of herbivory can prime plant defenses; however, few studies have explored how such cues elicit broader plant responses, including potential effects on plant growth and other resource allocations that may affect tolerance to herbivore damage. We exposed goldenrod plants (Solidago altissima) to varying concentrations of the putative sex pheromone of a gall-inducing herbivore, which has previously been implicated in defense priming. In experiments with two plant genotypes and three herbivore populations, any level of exposure to the pheromone enhanced tolerance of galling, rescuing flower production to levels observed for ungalled plants. Exposure to low doses of the pheromone elicited greater resistance to galling than exposure to high doses, with unexposed plants exhibiting intermediate resistance, suggesting a nonlinear relationship between exposure and defense priming. These findings suggest plant responses to environmental cues associated with biotic stressors are broader and more complex than previously appreciated.