UC Riverside

When damaged by herbivores, plants often produce and emit a suite of volatile organic compounds (VOCs). Research has shown a variety of functions for these VOCs in defense against herbivores across many plant species. In Chapter One, I outline the characteristics and the induction of VOCs. I then discuss the two main functions of VOCs, its role in within-plant signaling and its concurrent effect with plant-based resources on the predation and the colonization of an omnivorous predator.

In Chapter Two, I examined the role of VOCs as within-plant signals in Datura wrightii (Solanaceae) following damage by the herbivorous beetle, Lema daturaphila (Coleoptera: Chrysomelidae). Experimentally, I expose (receiver) leaves to VOCs emitted by a damaged (emitter) leaf on the same plant. I then applied herbivore damage to receivers and measured the subsequent VOC production from each leaf. I analyzed the VOCs produced by receivers based on exposure to VOCs from the emitter, and the amount of vascular connectivity that each receiver had with the emitter. I found that VOC exposure increased subsequent emissions in receivers in general; and particularly in receivers having no direct vascular connection to the emitter. These findings indicate the importance of VOCs as an airborne damage signal in D. wrightii in response to herbivory.

In Chapters Three and Four, I present my research on the concurrent effect of VOCs and plant-based resources on the predation of L. daturaphila and the colonization of D. wrightii by the omnivorous predator, Geocoris pallens (Hemiptera: Geocoridae). Through field and greenhouse experiments, I manipulated the presence of VOCs and plant-based resources at the host plant, D. wrightii. I then measured the effects of these manipulations on the rate of predation and the density of G. pallens. Both attractants positively increased the density of G. pallens, but plant-based resources strongly decreased predation of L. daturaphila by G. pallens. These findings indicate that different types of plant attractants may produce independent effects on predation vs. colonization in omnivores. Together, the research presented in this dissertation illustrate that VOCs emitted by D. wrightii play an integral part of the overall response to herbivory.