Undergraduate Honors Theses

Thesis Defended

Spring 2019

Document Type

Thesis

Type of Thesis

Departmental Honors

Department

Ecology and Evolutionary Biology

First Advisor

Deane M Bowers

Abstract

Caterpillars who feed on a wide variety of plant hosts must adapt to the defenses of every plant they feed on. For seed-eating caterpillars this can be particularly difficult because the seed is one of the most heavily defended bodies on a plant. Helicoverpa zea, the corn earworm, is both a seed eater and a generalist, feeding on plants belonging to over 30 families, including both agricultural crops and native plants, such as Lupinus texensis. I studied the corn earworm and L. texensis to answer three questions: i) what is the feeding behavior of these seed-eating caterpillars, ii) how do these generalists respond to the presence of quinolizidine alkaloids in their seed diet, and iii) what is the fate of these compounds after they are consumed by a generalist caterpillar?

I observed that corn earworms exhibit highly variable feeding behavior and travel around the plant to feed from dispersed sources on the plant. In order to understand the effect of plant toxin defense on caterpillar growth, I fed corn earworms on varying concentration diets of Lupinus texensis seeds (containing QAs). When monitoring their growth rate and mass in response to these various levels of plant defense chemicals, no difference was found between caterpillar development across different toxin levels. Instead, it appears that caterpillars which were exposed to greater QA levels ate greater quantities of food over all in order to account for the food’s lower digestibility. Preliminary chemical data suggest that the caterpillars do not house the defense chemicals in their body after consumption, instead excreting the defense chemicals in their frass (feces). These findings provide new insight into this agriculturally significant system, and how the behavior of a generalist feeder affects its seed predation.

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