Chemical communication in cerambycid beetles and the molecular basis of olfaction

Mitchell, Robert

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Description

Title

Chemical communication in cerambycid beetles and the molecular basis of olfaction

Author(s)

Mitchell, Robert

Issue Date

2012-05-22T00:19:34Z

Director of Research (if dissertation) or Advisor (if thesis)

• Hanks, Lawrence M.
• Robertson, Hugh M.

Doctoral Committee Chair(s)

Hanks, Lawrence M.

Committee Member(s)

• Robertson, Hugh M.
• Berenbaum, May R.
• Ginzel, Matthew D.

Department of Study

Entomology

Discipline

Entomology

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• odorant receptor
• chemoreceptor
• cerambycidae
• Longhorned beetle
• Pheromone
• chemical attractant
• mimicry
• chemical ecology

Abstract

Longhorned beetles of the insect family Cerambycidae are a highly diverse group of insects whose larvae bore into the stems of forbs and the wood and roots of trees, and the family contains numerous pests of agriculture, forestry, and structural timber. The reproductive biology of adult cerambycids is mediated by long-range volatile aggregation or sex pheromones, but the pheromone chemistry is highly conserved, and many species of beetles produce and respond to identical compounds. This parsimony may yield powerful and efficient means to control species that are pests, but the full extent of these pheromone “motifs” remains unknown, as are the mechanisms by which cerambycid species remain reproductively isolated in the face of identical pheromones. In this dissertation, I present research that catalogs and defines new motifs of cerambycid pheromones. I identified (E)-6,10-dimethyl-5,9-undecadien-2-ol (“fuscumol”) and its acetate as a conserved pheromone motif of the subfamily Lamiinae, and also as an attractant for some species in the subfamily Cerambycinae. I also described alkan-2-ones as a novel and potentially widespread motif of minor pheromone constituents in the subfamily Cerambycinae that may act to chemically separate cerambycid species. I also present a comprehensive survey of volatile chemicals produced by Megacyllene caryae Gahan, the painted hickory borer, a common cerambycid of eastern North American that mimics vespid wasps. Male M. caryae produce an unusually complex aggregation pheromone of at least nine components, and I describe several behaviorally active components from this blend. I also report that agitated beetles of both sexes produce spiroacetals, a class of chemicals used as alarm pheromones by many species of vespid wasps, suggesting that beetles produce these chemicals as a form of chemical mimicry to complement their physical resemblance to their models. Finally, I present research on the odorant receptors (Ors) of cerambycids, which are members of a family of receptors responsible for detecting volatile chemicals at the molecular level. I sequenced 57 Ors from RNA extracted from antennae of male and female M. caryae, and tested several receptors against pheromone components in a heterologous expression system. I identified Ors tuned to the three pheromone components (S)-2-methyl-1-butanol, (2S,3R)-2,3-hexanediol, and 2-phenylethanol. McOr3 and McOr20 are also sensitive to structurally-related chemicals that are pheromones of other cerambycid beetles, suggesting that orthologous receptors may be present across many cerambycid species. These Ors are the first to be functionally characterized from any species of beetle and lay the groundwork for understanding the evolution of pheromones within the Cerambycidae.

Graduation Semester

2012-05

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Copyright and License Information

Copyright 2012 Robert Mitchell

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