The Synchrony of Herbivore Presence, Induced Plant Volatiles, and Parasitoid Response

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Title: The Synchrony of Herbivore Presence, Induced Plant Volatiles, and Parasitoid Response
Author: Puente, Molly Elizabeth
Advisors: Coby Schal, Committee Member
Fred Gould, Committee Co-Chair
George Kennedy, Committee Co-Chair
Nicole Darnall, Committee Member
Nick Haddad, Committee Member
Abstract: Parasitoids find chemical volatiles produced by herbivore-damaged plants attractive. It has been suggested that by manipulating these volatiles in crop plants, biological control can be enhanced in agricultural systems. Before this technology is implemented, it is important to understand the dynamics of the system. I used two different modeling approaches to address this phenomenon. In the first model, I combined a modified predator-prey functional response equation with an age-structured herbivore population model. In the second model I took a spatially-explicit stochastic simulation approach and examined the Brassica oleraceae, Pieris rapae, and Cotesia rubecula system in more detail. I looked at the effects of plant induction delay, plant relaxation delay, herbivore density, and parasitoid host-age preference. In both models, parasitoids gained the most from signals when all herbivore instars were viable hosts, herbivore density was low, and relaxation delays were short. In the stochastic simulation model, shorter induction delays could lead to considerable gains for the parasitoids. Together, the models indicate that there are some conditions that favor parasitoids following herbivore-induced plant volatiles. By creating plants that produce signals in the right time frame, it may be possible to optimize biological control. However, it is also apparent from my models that herbivore-induced volatiles are ineffective during herbivore outbreaks because parasitoids are limited by factors other the time it takes to find hosts, which is the primary way herbivore-induced plant volatiles aid foraging parasitoids. Improving biological control is one of the practices growers can adopt as part of Integrated Pest Management (IPM), and in the final section of this dissertation I discussed a survey exploring how growers adopt IPM. I found that practices consistent with IPM were adopted in a piecemeal fashion by cotton growers in Eastern North Carolina. My analysis indicated that growers did not see all these practices as part of a single management decision, but rather as parts of independent decisions dealing with weed management, insect management, crop management, and ecosystem management.
Date: 2007-07-18
Degree: PhD
Discipline: Entomology

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