Fig. 1.

Representative examples of GC-EAD recordings (total 170 runs) from male and female I. typographus tested on natural volatiles collected from intact bark from standing or felled trees. a Example for the entire chromatogram from a sun exposed standing tree. Upper signal trace is FID signal and the two lower traces are corresponding recordings of antennal electric potentials of one male and one female beetle. b Volatiles from a felled tree sampled at the day of first attack (25 April) and c late in June. The graphs in b and c show only the part of the chromatogram where oxygenated compounds elute on a HP-5MS column. 1) styrene 2) α-pinene 3) sabinene 4) β-pinene 5) myrcene 6) 3-carene 7) p-cymene 8) limonene 9) 1,8-cineole (1,3,3-trimethyl-2-oxabicyclo[2.2.2]octane) 10) γ-terpinene 11) 4-thujanol; (synonym sabinene hydrate, 5-isopropyl-2-methylbicyclo[3.1.0]hexan-2-ol) 12) terpinolene 13) camphor (1,7,7-trimethylbicyclo[2.2.1]heptan-2-one) 14) pinocamphone (2,6,6-trimethylbicyclo[3.1.1]heptan-3-one) 15) pinocarvone (6,6-dimethyl-2-methylenebicyclo[3.1.1]heptan-3-one) 16) isopinocamphone (2,6,6-trimethylbicyclo [3.1.1]heptan-3-one) 17) 4-terpineol (1-isopropyl-4-methyl-3-cyclohexen-1-ol) 18) 4-allylanisole (estragole). IS) Internal quantification standard, heptyl acetate.?) Unidentified compound; Responses at the elution time of the internal standard are due to an unidentified co-eluting compound. Most recordings showed no responses to the internal standard. One strong response in some samples correlates well to nonanal, but response to synthetic nonanal could neither be observed in EAD- nor in SSR-recordings