Plant perception of herbivore odors: Exposure of host plants to the putative pheromone of a specialist herbivore primes herbivore-induced volatile production

Background/Question/Methods

Olfactory cues play important roles in plant-insect interactions, and especially in plant defense against herbivores. Plants produce characteristic blends of volatile compounds in response to herbivore damage, and previous work has shown that these herbivore-induced plant volatiles (HIPVs) provide olfactory information for insects as well as neighboring plants. Volatiles from damaged plants may repel ovipositing insect pests and recruit predators and parasitoids that kill feeding herbivores. Many plants can also perceive the odors given off by their insect-damaged neighbors and respond by priming their anti-herbivore defenses. We recently discovered that some plants even utilize olfactory cues given off directly by their insect herbivores to help predict future herbivore attack. Our previous work has shown that tall goldenrod (Solidago altissima) plants exposed to the putative sex attractant of the specialist gall fly Eurosta solidaginis exhibit enhanced anti-herbivore defenses, including reduced palatability and stronger induction of the defense phytohormone jasmonic acid. Here, we demonstrate that exposure to the E. solidaginis emission also primes herbivore-induced volatile production in S. altissima.

Results/Conclusions

We found that S. altissima plants exposed to the E. solidaginis pheromone emitted higher quantities of both day and night HIPVs compared to unexposed control plants. This phenomenon appears to occur between co-evolved plant and insect species, as we did not observe any evidence of priming in non-host maize plants (Zea mays) exposed to the E. solidaginis emission. Our results also provide further evidence against a possible alternative hypothesis that the emission is directly deterrent to feeding herbivores. We found no evidence that emission-exposed squash (Cucurbita pepo) or aster (S. lateriflorum) plants repelled herbivores or were less palatable than unexposed plants. Together these results indicate that S. altissima plants respond physiologically to the emission of a co-evolved insect herbivore by enhancing their defense responses.