Chemical Ecology, Göteborg University, Box 461, 405 50 Göteborg, Sweden.
This work was done in order to investigate the chemical cues that guide the female Rhopalicus tutela to the oviposition sites. Certain oxygenated monoterpenes, associated with the bark beetle hosts, were found to be of particular importance in host location. These compounds elicit responses in bioassays (Y-tube) and in electrophysiological recordings (GC-EAD) while monoterpene hydrocarbons, constitutive odors from the host trees, in most cases do not elicit any significant EAD-responses. Odors from susceptible bark beetle hosts on host trees (Picea abies) were collected by solid phase micro extraction (SPME) fibers coated with partially crosslinked carbowax/divenylbenzene (df 65 µm), and 70 mg Porapak®Q tubes. Sampled odors were investigated by chemical (GC-MS) and electrophysiological analysis. The advantage of SPME in GC-EAD is that the sampling time is relatively short, furthermore it enables an EAD-recording without the possible interference a solvent. However, larger amounts of compounds is captured in the eluate from the Porapak®Q sampling, that also makes it possible to expose more than one individual to exactly the same stimuli. The pteromalid parasitoid R. tutela is a natural enemy of Ips typographus, and some other economically important bark beetle species, breeding in conifers. R. tutela attack late instar larvae and pupae in pupal chambers concealed under the bark. Walking on the bark surface, female parasitoids locate pupal chambers and conduct oviposition through the bark.