Date on Senior Honors Thesis

5-2019

Document Type

Senior Honors Thesis

Degree Name

B.A.

Department

Biology

Degree Program

College of Arts and Sciences

Author's Keywords

indole; herbivores; volatiles; sensitivity

Abstract

When plants in nature are attacked by herbivores, they frequently release airborne volatiles. These herbivore-induced plant volatiles (HIPVs) help plants defend themselves against herbivore attack by calling in natural enemies, but HIPVs may also be directly toxic to herbivores. Indole (C8H7N) is a common HIPV that is toxic to caterpillars, but its relative toxicity to different caterpillars has not been explored. I tested the toxicity of indole on six caterpillar species (Spodoptera frugiperda, Trichoplusia ni, Spodoptera exigua, Anticarsia gemmatalis, Heliothis virescens, and Helicoverpa zea). Results show that indole is most toxic to Trichoplusia ni and Anticarsia gemmatalis, moderately toxic to Heliothis virescens, and least toxic to Spodoptera frugiperda, Spodoptera exigua, and Helicoverpa zea. The results of this study suggest that there is a relationship between indole sensitivity and host range of a caterpillar species, and that species with narrower host ranges are more sensitive to indole. This information provides a useful foundation for studying plant defenses, because the toxicity of most plant defense compounds is unknown for most herbivore species.

Lay Summary

When plants get attacked by different insects in nature, such as caterpillars, they release chemicals into the air. These chemicals help plants defend themselves from being attacked further by attracting predators of the caterpillars that are attacking the plant. Not only are these chemicals toxic when released into the air, but they are also toxic when consumed by the caterpillars. One common chemical that plants release when they are under attack is called indole. We know that indole can be toxic, but we do not know how toxic it is or how it might affect different caterpillar species differently. This study tested the toxicity of indole to six different caterpillar species (Spodoptera frugiperda, Trichoplusia ni, Spodoptera exigua, Anticarsia gemmatalis, Heliothis virescens, and Helicoverpa zea). The results of this study show that indole is most toxic to Trichoplusia ni and Anticarsia gemmatalis, moderately toxic to Heliothis virescens, and least toxic to Spodoptera frugiperda, Spodoptera exigua, and Helicoverpa zea. These results suggest that there may be a relationship between how toxic indole is to caterpillar species and the range of plants that these species are able to consume. This information provides a foundation for studying how plants defend themselves, because the toxicity of most plant defense chemicals on most caterpillar species is unknown.

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