Microbial volatile emissions as insect semiochemicals

Authors: DAVIS, THOMAS - University Of Idaho; Crippen, Tawni - Tc; HOFSTETTER, RICHARD - Northern Arizona University; TOMBERLIN, JEFFREY - Texas A&M University

Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/4/2013
Publication Date: 6/25/2013
Publication URL: http://handle.nal.usda.gov/10113/58264
Citation: Davis, T.S., Crippen, T.L., Hofstetter, R.W., Tomberlin, J.K. 2013. Microbial volatile emissions as insect semiochemicals. Journal of Chemical Ecology. 39:840-859.

Interpretive Summary: We describe the interactions between microorganisms (bacterial and fungal) and insects through signaling molecules in the form of chemical substances that vaporize into the air (volatiles). The worldwide distribution of microorganisms allows for frequent interactions between insects and microbes. Many of the volatiles produced by microbes are associated with insect attraction and some are powerful repellants. We explored important pathways involved in the production of these volatiles and evaluated the effect of these signals from an ecological context. Large groups of closely related microorganisms have many pathways in common for the production of volatiles. In turn, a single volatile can have different effects on the behavior of different insects. For example, they may signal aspects of habitat suitability, alert to the potential exposure to dangerous pathogens, spur arthropod aggregation, or prompt mating and egg laying behaviors from insects. We hypothesize that insect responses to volatiles from microorganisms are much more common than we currently think, and these signals represent evolutionary “infochemicals” that may contribute to insect behavioral responses.

Technical Abstract: We provide a synthesis of the literature describing biochemical interactions between microorganisms and arthropods by way of microbial volatile organic compound (MVOC) production. We explored important metabolic pathways involved in MVOC production and evaluated the functionality, generality, and ecological context of MVOC signals. The cosmopolitan distribution of microorganisms creates a context for frequent, and frequently overlooked, interactions between arthropods and microbial species. Many biochemical pathways for behaviorally active volatile production by microbial species are conserved across large taxonomic groupings of microorganisms. In addition, there is substantial functional redundancy in MVOCs. Fungal tissues commonly produce polyketides and short-chain alcohols, whereas bacterial tissues tend to be more commonly associated with amines and pyrazines. There are numerous instances of MVOCs being closely associated with insect feeding behaviors, but some MVOCs are also powerful repellants. Emissions from microorganisms in situ may signal aspects of habitat suitability or potential exposure to entomopathogens. In some systems, bacterial or fungal volatiles can also incite arthropod aggregations, or MVOCs can resemble sexual pheromones that elicit mating and oviposition behaviors from responding arthropods. A single microorganism or MVOC can have different effects on the behavior of arthropods, especially across species, ontogenies, and habitats. There appears to be a multipartite basis for interactions between arthropods and MVOCs, and complex tritrophic interactions can result from the production of MVOCs. We hypothesize that arthropod olfactory responses to emissions from microorganisms inhabiting their sensory environment are much more common than currently recognized, and these signals represent evolutionarily reliable infochemicals. Such diffuse interactions may contribute to the formation of neutral, beneficial, or even harmful symbioses and provide considerable insight into the evolution of insect behavioral responses to volatile compounds.