Date of Award

1990

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Entomology

First Advisor

David J. Boethel

Abstract

Research was conducted to determine the impact of the allelochemical, $\alpha$-tomatine, on the susceptibility of the lepidopterous pests, Heliothis zea (Boddie) and Pseudoplusia includens (Walker) to the entomogenous fungus, Nomuraea rileyi (Farlow) Samson. In one experiment, $\alpha$-tomatine inhibited colony formation and growth of N. rileyi, in vitro. In vivo, larval growth and developmental time of H. zea were affected by $\alpha$-tomatine and N. rileyi. The fungus was detected in the hemolymph and tissue of larvae treated with two concentrations (LC$\sb{50}$ and LC$\sb{90}$) of N. rileyi conidia, including those fed $\alpha$-tomatine. At the LC$\sb{50}$, $\alpha$-tomatine protected larvae against N. rileyi and increased survivorship; at the LC$\sb{90}$, it inhibited the development of N. rileyi, thereby reducing production of conidia. In a second experiment, larval weight of P. includens was decreased by increasing concentrations (0.001 to 0.10% wet weight of diet (wwt)) $\alpha$-tomatine. A linear regression (Y = 217.86 $-$ 2,089.53 X, r$\sp2$ = 0.90) described the relationship between the larval growth of P. includens and the $\alpha$-tomatine concentrations. The effective dose required to reduce larval weight by 50% was calculated (ED$\sb{50}$ = 0.048% wwt) and then validated in a subsequent experiment. In that study, a significant reduction (P $\leq$ 0.05) in mean body weight of 10- and 12-day-old larvae was obtained in larvae fed diet containing $\alpha$-tomatine when compared with larvae in the control. In a third experiment, N. rileyi was detected in the hemolymph and tissue of P. includens larvae treated with two concentrations (LC$\sb{50}$ and LC$\sb{90}$) of conidia, including those fed $\alpha$-tomatine. At the LC$\sb{90}$, $\alpha$-tomatine protected larvae against N. rileyi and increased survivorship; at the LC$\sb{50}$, it inhibited the production of conidia of N. rileyi. Results from these experiments demonstrated that $\alpha$-tomatine exerted antagonistic effects against N. rileyi, and retained its antifungal qualities at the third trophic level, inhibiting the development of N. rileyi in P. includens and H. zea. In addition, these studies demonstrated that generalist insect-heribivores that tolerate $\alpha$-tomatine may be protected against entomopathogenic fungi.

Pages

96

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