Comparing defense priming of squash plants (Cucurbita pepo) against specialist and generalist herbivores

In response to being fed on by herbivores, plants produce volatile compounds that play important roles in plant defense. A relatively recent discovery revealed that undamaged neighboring plants can detect these volatiles as a warning of possible future herbivore attack and respond by priming their anti-herbivory defenses. Primed plants typically mount a faster or stronger defense after an herbivore begins feeding. Plant volatile-mediated priming has been observed in many plant species but has not yet been documented in the family Cucurbitaceae. Therefore we sought to test if squash plants (Cucurbita pepo) respond to volatiles from herbivore-damaged plants by priming their defenses. Our objectives were to 1) evaluate plant priming in response to specialist herbivores and 2) evaluate plant priming in response to generalist herbivores. For our first objective, emitter plants were either damaged by specialist striped cucumber beetles (Acalymma vittatum) or left as undamaged controls. Neighboring “receiver” plants were exposed to damage or control emitter volatiles for 24 hours and then challenged with herbivory by beetles. For our second objective, we employed the same experimental design but used generalist corn earworms (Helicoverpa zea). We quantified the amount of herbivory on receivers and found no difference in plant damage between receivers exposed to volatiles from specialist-damaged and undamaged emitters. In contrast, receivers of generalist-damage volatiles sustained more damage relative to receivers of undamaged control volatiles. Taken together, our findings contribute to a better understanding of plant defense priming and offer insight into how plants predict and defend against different herbivore species.