## 2 Materials and Methods
### Field Collection of Distributed VOCs Emitted by the Ips typographus Naturally Infested Pica  
We conducted two collections of VOCs from naturally infested trees in the field at different locations and during different periods of the 2022 growing season. In this study, we did not measure VOCs from non-infested trees as controls. This decision stems from the continuation of our prior study [8] and existing literature reports (Table 1), which have consistently demonstrated several-fold increases in emissions from infested trees using similar techniques. Both collections took place on the Forests CZU property near Kostelec nad Cernymil key, the Czech Republic. The area is characterized by a mature forest primarily composed of a 90-year-old Norway spruce (_P. abies_) plantation, situated at an altitude of 400-450 m above sea level (Figures 2 and 3). The distributed VOCs were collected within 900 m around the freshly _Ips typographus_-infested individual Norway spruces. The infestation status was found by the occurrence of fresh frass at the stem's base, and infestation stadia were specified by assessing the beetle attack density exhibited by the sampled tree. Both sampled trees were in the nuptial chamber building attack stadia, approximately two weeks from the beginning of the mass attack. The VOCs were collected from infested trees at three different height levels from the ground (1.3 m, 2.6 m, and 4 m). Collection chambers were placed at three different distances from the tree trunk (5 cm, 100 cm, and 900 cm away from the tree) (Figure 3). The row of collection chambers was oriented in four cardinal directions: north (N), east (E), south (S), and west (W) (see Figures 2-4 for reference). Dataloggers were used throughout the experiment to measure the temperature and humidity (Tables S1 and S2), and an anemometer was used to measure the wind speed (Figures 2 and 3). Figure 1: Volatile collection of \(\alpha\)-pinene under laboratory conditions from fresh drilled logs of _Pica abies_. (**a**) The collection of \(\alpha\)-pinene occurred across three height levels, namely L1, L2, and L3. (**b**) Top view of the log pile; black dots indicate distances between the bark surface and the point of collection of \(\alpha\)-pinene for each level. Two analytical approaches were employed to collect VOCs from infested trees in natural forest conditions [27; 28; 45]:  
Sorption onto SPME fibers (PDMS/CAR/DVB, Supelco, PA, USA): Eight SPMEs fixed in protective chambers were positioned at three height levels: L1 (130 cm), L2 (240 cm), and L3 (400 cm). They were placed at two distances from the tree (5 cm and 100 cm) in the immediate proximity of the tree in four cardinal directions: north, south, west, and east. Additionally, four fibers were positioned 900 cm away from the tree in the same direction. These SPMEs were exposed for 60 min to collect volatile organic compounds (VOCs) from the forest air. After collection, the fibers were sealed in vials with septa in the same manner as in the laboratory. They were then placed on dry ice and subsequently stored in a freezer at \(-18\)\({}^{\circ}\)C before undergoing measurement using Gas Chromatography-Flame Ionization Detection GC-FID, Agilent 8890 (Agilent, CA, USA). Figure 3: Study site for the second forest spatial VOC measurement around the infested tree (24 August 2022) for data in the CZU Forests close to Vyzlovka, the Czech Republic (49.981 N, 14.801 E). Black points—sampling points; red points—Norway spruce infested trees; green—healthy Norway Spruce trees; brown points—dead Norway Spruce trees; blue points—Scot pines; yellow points—beech trees. Figure 2: Study site for the first forest spatial VOC measurement around the infested tree (30 June 2022). Locality Forests CZU close to Stribrná Skalice, the Czech Republic (49.913 N, 14.863 E).