A single compound in the goldenrod gall fly (Eurosta solidaginis) volatile emission primes anti-herbivore defenses in tall goldenrod (Solidago altissima)

Insect feeding damage is known to induce plant defenses. More recent discoveries have found that plants can also perceive environmental cues associated with the presence of insect herbivores, allowing them to prepare their defenses for future attack. For example, plants may detect insect footsteps or oviposition, and some even use olfactory cues to sense the presence of nearby herbivores. Several studies have found that undamaged plants can eavesdrop on volatiles emitted by their insect-damaged neighbors and respond by enhancing their own anti-herbivore defenses. Adding to these findings, our previous work has shown that some plants can also perceive and respond to olfactory cues emitted directly by insect herbivores. More specifically, tall goldenrod (Solidago altissima) plants exposed to the putative sex attractant of the specialist gall fly Eurosta solidaginis exhibited enhanced anti-herbivore defenses, including reduced palatability and stronger induction of the defense phytohormone jasmonic acid. In the current study, we investigated the ability of S. altissima plants to perceive and respond to individual compounds in the E. solidaginis emission. We found that goldenrod plants exposed to the most abundant compound in the fly emission exhibited an enhanced defense response similar to plants exposed to the entire emission blend. These findings support our previous work suggesting that goldenrod plants eavesdrop on the olfactory signals of E. soldiaginis and offer some insight into the specificity of S. altissima perception of olfactory cues.