The Influence of Chirality on the Behavioral Responses of Longhorned Beetles (Coleoptera: Cerambycidae) to Volatile and Contact Pheromones

Gabriel P Hughes, Purdue University

Abstract

In this dissertation, I present research I conducted to test the hypothesis that chirality influences the behavioral responses of longhorned beetles to volatile and contact pheromones. Structures of pheromones in the longhorned beetles generally fall along taxonomic lines, and various structural modifications such as functional groups and stereochemistry are used to grant species specificity to these signals. Effects of chirality on the bioactivity of volatile pheromones has been documented in the longhorned beetle subfamily Cerambycinae, but little is known about how stereochemistry affects behavioral responses of conspecifics to contact pheromones in this subfamily, and volatile pheromones in the Lamiinae. In Chapter 1, I review the current literature on pheromones in the longhorned beetles. I summarize known components and discuss how chirality affects behavioral responses to these compounds. In Chapter 2, I test the hypothesis that males of the North American lamiine species, Astyleiopus vareigatus, produces fuscumol, fuscumol acetate or both, concordant with field trials in which members of this species were attracted to these compounds. I found that male A. variegatus pheromone consists of (S)-fuscumol and (S)-fuscumol acetate in a ratio of approximately 1:2. In Chapter 3, I test the hypothesis that stereochemistry grants species specificity to the common lamiine pheromones fuscumol and fuscumol acetate. I found that traps baited with enantiomers of fuscumol or fuscumol acetate, either singly or in pairs, captured the following species in a treatment-specific way: Astyleiopus variegatus, Graphisurus fasciatus, Aegomorphus modestus, Astylidius parvus, and Astylopsis macula. My data suggest that chirality plays a role in maintaining species specificity in the pheromone channel, and that these compounds are likely produced by these species. In Chapter 4, I test the hypothesis that chirality of the methyl group on the hydrocarbon contact sex pheromones of Neoclytus acuminatus acuminatus influence the behavioral response of males. I found that chirality of the major component is most important, and that the natural R-enantiomer is more bioactive than the S-enantiomer. I also found that the minor components augment the response of the male to the major component, and that even S-minor components appear to have a small degree of bioactivity. In Chapter 5, I use a differential expression approach to investigate genes involved in pheromone biosynthesis in the cerambycine Neoclytus mucronatus mucronatus. I used RNA-seq to compare the expression levels of pheromone biosynthetic genes in predawn, calling and non-calling beetles at noon. I found that expression levels of both of the noon treatments appeared similar, but that non-calling beetles expressed levels of short-chain dehydrogenase/reductase and α-esterase transcripts that were greater than that expressed in the predawn beetles. These are among the first steps towards understanding pheromone biosynthesis in this subfamily of longhorned beetles. Moreover, identifying genes responsible for the specific stereochemistry of pheromones will lead to a better understanding of how these insects establish and maintain species-specific chemical signals.

Degree

Ph.D.

Advisors

Ginzel, Purdue University.

Subject Area

Entomology

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