Electrophysiological and Behavioral Responses of the Bark Beetle Dendroctonus rhizophagus to Volatiles from Host Pines and Conspecifics

The bark beetle is endemic to northwestern Mexico where it kills immature pines < 3 m tall. We report the first investigation of the chemical ecology of this pest of forest regeneration. We used GC-EAD to assess olfactory sensitivity of this species to volatile compounds from: resin of a major host, ; mid/hindguts of single, gallery-initiating females; and mate-paired males within galleries of attacked host trees in the field. Antennae of both sexes responded to monoterpenes -pinene, -pinene and 3-carene as well as to the beetle-derived oxygenated monoterpenes fenchyl alcohol, myrtenal, -verbenol, -verbenol, verbenone, and myrtenol. These monoterpenes were quantified from pre-emerged adults forced to attack host tissue in the laboratory, and from individuals dissected from naturally-attacked hosts at different stages of colonization. In both bioassays, myrtenol and -verbenol were the most abundant volatiles, and -verbenol was the only one produced in significantly greater quantities by females than males in a naturally-colonized host. Two field experiments were performed to evaluate behavioral responses of to antennally-active monoterpenes. Results show that 3-carene was significantly attractive either alone or in a ternary (1:1:1) combination with -pinene and -pinene, whereas neither -pinene nor -pinene alone were attractive. None of the beetle-associated oxygenated monoterpenes enhanced the attractiveness of the ternary mixture of monoterpenes, while verbenone either alone or combined with the other five oxygenated terpenes reduced attraction to the ternary mixture. The results suggest that attraction of to the host tree is mediated especially by 3-carene. There was no conclusive evidence for an aggregation or sex attractant pheromone.