Odor perception in the bark beetle parasitoid Roptrocerus xylophagorum exposed to host associated volatiles

Y-tube olfactometer bioassays and combined gas chromatography-electroantenn ographic detector (GC-EAD) analyses were performed to investigate the speci fic odors utilized as host location cues by the bark beetle parasitoid, Rop trocerus xylophagorum, originating from the southeastern United States. R. xylophagorum parasitizes several economically important holarctic bark beet le species and females oviposit preferentially on late larval stages. Both female and male parasitoids were tested with volatiles derived from host in festations of either Dendroctonus frontalis, the southern pine beetle, or I ps grandicollis, the southern pine engraver. Tested volatiles were steam di stillates from the bark of loblolly pine, Pinus taeda, infested with larvae of the respective bark beetle species. Combined gas chromatography-mass sp ectrometry (GC-MS) was employed for identification and quantification of th e compounds in the steam distillates. To confirm the EAD activity of identi fied compounds, GC-EAD analyses were repeated with a synthetic blend compos ed predominantly of compounds in the crude extracts that had revealed appar ent electrophysiological activity. In Y-olfactometer bioassays, female para sitoids were attracted to both of the above-mentioned distillates. Male par asitoids were tested with one of the distillates but failed to respond. In GC-EAD analyses, the sexes displayed similar relative sensitivities to the components of the blends. Males exhibited generally higher amplitudes of re sponse to the tested compounds than females. Monoterpene hydrocarbons assoc iated with the constitutive resin of the host tree did not elicit significa nt EAD responses. Compounds known to be associated specifically with the ho st-tree complex, such as certain oxygenated monoterpenes, generated the gre atest EAD responses. Female parasitoids were attracted by a synthetic blend composed of several of the EAD active oxygenated monoterpenes.