Influence of a gall inducing herbivore on the chemical defense of tall goldenrod (Solidago altissima L.) through time

Many plant-insect interactions are mediated by chemicals in the environment. In many systems, herbivore-associated cues can trigger plant chemical defenses, a phenomenon known as priming. Such defenses are mediated by phytohormones including jasmonic acid and salicylic acid. The relationship between tall goldenrod, Solidago altissima L. (Asteraceae), and the goldenrod gall fly, Eurosta solidaginis Fitch (Diptera: Tephritidae), is an example of an interaction mediated by chemical signals. Male E. solidaginis emit a sex pheromone that primes S. altissima. However, the primed state of S. altissima is not well described, namely the duration of enhanced chemical defense after a challenge. Studies have shown that specialist chewing herbivory is decreased on primed S. altissima. We therefore hypothesized that primed plants will rapidly induce chemical defense following insect attack and jasmonic acid levels will remain higher and last longer than in an unexposed plant. To test this, we conducted feeding assays on S. altissima plants exposed to the pheromone of E. solidaginis while controlling for herbivory and exposure. We quantified phytohormones in damaged leaves harvested at five time points over 48 hours. We used vapor phase extraction to prepare samples for gas chromatography-coupled mass spectrometry, which we used to quantify concentrations of jasmonic acid, salicylic acid, auxin and abscisic acid. Our findings will contribute valuable temporal information about the primed state in S. altissima. Additionally, this work will create a comparative framework to describe the response of primed plants to generalist herbivory.