Through the “arms race” of antagonistic co-evolution, plants have evolved to recognize herbivore-specific volatile chemicals in their environment. After perceiving such a cue, plants may induce preparatory chemical defenses, a phenomenon referred to as “priming”, which readies a rapid defense response to a later challenge such as herbivory or infection. Recent discoveries in the co-evolutionary relationship of tall goldenrod (Solidago altissima L., Asteraceae) and the goldenrod gall fly (Eurosta solidaginis Fitch, Tephritidae) have demonstrated that priming plays an important role in the mediation of their host-parasite interactions: adult male gall flies emit a volatile pheromone on goldenrod plants to attract mates, then mated E. solidaginis females lay their eggs in the growing apical bud of S. altissima, where the larva hatches and induces a gall. Nearby S. altissima plants are primed by the male pheromone signal and are more resistant to galling from the E. solidaginis larva as well as specialist beetle herbivory. Despite a rich body of research on the chemical ecology of goldenrod and its gall fly, the molecular underpinnings of priming, including what gene expression patterns are involved in the rapid mobilization of plant defenses post-pheromone perception, are still not well understood. Until now, the Solidago-Eurosta system has not been studied using transcriptomic tools; this ecological model system is fertile ground for understanding the genes underlying plant priming. Additionally, primed S. altissima plants are less palatable to specialist herbivores, but it is not confirmed whether generalist species are similarly deterred. We investigated the phytohormone and transcriptomic profile of S. altissima plants primed by E. solidaginis pheromone before and after herbivory from a generalist caterpillar. To measure chemical defense, we extracted leaf phytohormones from primed and naïve (unprimed) plants that were damaged by caterpillars and quantified defense-related hormones such as jasmonic acid and salicylic acid with gas chromatography-coupled mass spectrometry (GC-MS). Illumina RNAseq was obtained for damaged leaves and the Trinity pipeline was used for assembly and differential gene expression (DGE) analyses. Our phytohormone results coupled with DGE analysis illustrate the influence of a co-evolved specialist on generalist herbivory and offer insight into the molecular signatures of defensive priming in plants.