Volatile attractants for three Pteromalid parasitoids attacking concealed spruce bark beetles

The odour perceptive abilities, and preferences, of three bark beetle paras itoid species; Rhopalicus tutela (Walker), Roptrocerus mirus (Walker), and Roptrocerus xylophagorum (Ratzeburg) (Hymenoptera: Pteromalidae), were inve stigated to isolate and identify the essential compounds involved in host l ocation. These parasitoids attack several economically important bark beetl e species and oviposit preferentially on late larval stages concealed under the bark of conifers. Odours were collected from Norway spruce logs (Picea abics L. Karst.) containing Ips typographus L. (Coleoptera: Scolytidae) la rvae. Biologically active compounds were isolated by coupled gas chromatogr aphic-electroantennographic detection (GC-EAD), and identified by GC-mass s pectrometry (GC-MS). Based on these analyses, four different synthetic bait s were prepared and tested in a Y-tube walking bioassay. In the complex odo ur samples from spruce logs, only 16 compounds were EAD-active. The tested R. tutela and R, mirus females displayed similar trends in antennal activit y to EAD-active compounds, responding mainly to oxygenated monoterpenes tha t indicate damaged conifers. Consequently, the synthetic baits were exclusi vely prepared with oxygenated monoterpenes. Parasitoid females (X. tutela a nd R. mirus) preferred spruce logs containing susceptible hosts over fresh logs, while male parasitoids (R, mirus) did not show any preference. Howeve r, when odours from fresh logs were mi?;ed with synthetic baits (mimicking the odour composition of logs containing susceptible hosts), these combinat ions attracted female parasitoids (R. tutela, R. mirus, and R. xylophagorum ). All synthetic baits seemed to be equally attractive to female parasitoid s.