Volatiles from Potential Hosts of Rhopalicus tutela a Bark Beetle Parasitoid

Host location cues for parasitic wasps that attack bark beetle larvae concealed under the bark of spruce trees were analyzed by collecting odor samples from entrance holes into the bark beetle galleries, isolated larvae, and pupal chambers with or without bark beetle larvae. Odor samples were collected by dynamic headspace adsorptions on Porapak Q or static adsorptions by using solid-phase microextraction (SPME) with Carbowax–divinylbenzene as the adsorbing phase. Samples were analyzed by coupled gas chromatographic–electroantennographic detection (GC-EAD) and GC-mass spectrometry (GC-MS). The antennae of Rhopalicus tutela females responded primarily to oxygenated monoterpenes that are typical for damaged host trees. These compounds are attractive to bark beetle parasitoids in long-range host location, suggesting that they are used in both long- and short-range host location. No differences could be detected between samples collected from pupal chambers with or without mature larvae. Larvae outside pupal chambers emitted low quantities of the same compounds present in empty pupal chambers. The data support the hypothesis that volatiles used by host foraging parasitoids arise from the interaction between introduced microorganisms and the bark and/or vascular tissue of the host tree rather than from the bark beetle larvae.