Volatile compounds in the larval frass ofDendroctonus valens andDendroctonus micans (Coleoptera: Scolytidae) in relation to oviposition by the predator,Rhizophagus grandis (Coleoptera: Rhizophagidae)

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During a laboratory study evaluatingRhizophagus grandis (a specific native predator of the Eurasian bark beetle,Dendroctonus micans), as a potential biocontrol agent against the North American bark beetle,Dendroctonus valens, it was found that feeding larvae and laboratory-produced frass of the potential prey elicited very high oviposition responses in the predator. Comparative chemical analysis of this laboratory-produced larval frass revealed that one major volatile compound, (-)-fenchone, is associated with the larvae of bothDendroctonus species.D. micans also generated pinocamphone while oxygenated monoterpenes in the frass ofD. valens were camphor,cis-4-thujanol, fenchol, terpinen-4-ol, myrtenal, pinocarvone, borneol, verbenone, piperitone, campholenaldehyde,trans-myrtanol,cis-myrtanol,p-cymen-8-ol and 5-oxo-camphor. This range of prey-produced compounds with a possible biological effect onR. grandis was narrowed down subsequent to comparative analysis of field-collected larval frass. (-)-Fenchone, pinocamphone, camphor, terpinen-4-ol, borneol, fenchol, and verbenone were found to be common to both prey species. A mixture of these seven components was tested in a bioassay, where it elicited as much oviposition as did larval frass ofD. micans. The oviposition stimulants forR. grandis are thus clearly among the mixture's constituents.