First report: Xylosandrus compactus (Eichhoff, 1876), new invasive ambrosia beetle in Montenegro

Key message

The ambrosia beetle Xylosandrus compactus (Eichhoff, 1876), originally from Southeast Asia, was first found in Europe in 2010, specifically in Italy. Since then, X. compactus has rapidly spread across southern Europe, including France, Spain, Greece, Turkey, Malta, Slovenia, Russia, Croatia, and Switzerland, gradually moving northward through lower-elevation areas. In 2023, a single female was found near the village of Kameno in Montenegro. This female was sifted through leaf litter in rocky terrain within a deciduous forest mainly populated by oak and hornbeam trees, located 2.5 km from the international port of Herceg Novi.

1 Context

Invasive species impose a considerable economic burden on individual economies and pose a significant threat to biodiversity (InvaCost 2024). Europe is currently home to 42 species of invasive bark and ambrosia beetles (Alonso-Zarazaga et al. 2023; Mas and Johnson 2023; EPPO 2024; Gebhardt et al. 2024; Knížek and Smith 2024; Toccafondi et al. 2025). Among them, Xylosandrus compactus (Eichhoff, 1876) causes damage to shrubs and trees in forests, ornamental gardens, and parks (Garonna et al. 2012; Vannini et al. 2017; Leza et al. 2020). This species harms thin twigs, causing them to wither and die (Pennacchio et al. 2012; Vannini et al. 2017; Gugliuzzo et al. 2019a) while also serving as a vector for various fungal pathogens (Bateman et al. 2016; Vannini et al. 2017; Morales-Rodríguez et al. 2021). In exceptional cases, it can even infest tree trunks with a diameter of up to 80 cm (Gugliuzzo et al. 2019b). With a host range exceeding 220 plant species (Gugliuzzo et al. 2023), monitoring its spread is essential.

X. compactus is originally from Southeast Asia (Wood 1982) and was first observed in Europe in Italy in 2010 (Pennacchio et al. 2012), followed by detections in France in 2015 (Chapin et al. 2016), Spain in 2019 (Leza et al. 2020), Greece in 2019 (Spanou et al. 2019), Turkey in 2021 (Hizal et al. 2023), Malta in 2021 (EPPO 2021), Slovenia in 2023 (Hauptman et al. 2024), the European part of Russia in 2023 (Karpun et al. 2024), Switzerland in 2023 (Blaser et al. 2024), and Croatia in 2023 (Pernek et al. 2025).

X. compactus has been rapidly spreading across southern Europe since 2010 and is gradually extending northward (see Blaser et al. 2024). Although this expansion is currently confined to lower elevations, the prediction model made by Urvois et al. (2021), suggesting that X. compactus would not reach the Baltic Sea coast until approximately 2050, may no longer be valid.

This article reports a new occurrence of the X. compactus in Montenegro.

2 Material and methods

In 2023, sifting studies were conducted at various locations in Montenegro. The study took place from October 28 to November 4, 2023, at sites in National Park Durmitor, National Park Biogradska Gora, and surroundings of Boka Kotorska bay. A circular sieve with a diameter of 28 cm and a mesh size of 0.4 × 0.4 cm was used for sifting. Approximately 5–15 L of material was examined during each sifting event. The material was placed in Berlese-type extractors, and collected beetles were preserved in ethyl acetate.

For the generic and species-level identification of the specimen, morphological characters described by Gomez et al. (2018) and Smith et al. (2020) were used. The total length of the specimen is 1.77 mm, measured from the anterior margin of the pronotum to the apex of the elytra.

3 Results and discussion

On November 4, 2023, a single live, dormant female specimen of X. compactus (leg. Adam Šíma, Czech Republic) (Fig. 1) was found in a soil sample from a deciduous forest dominated by oak (Quercus spp.) and hornbeam (Carpinus spp.) near the village of Kameno (42.4727 N, 18.5288E), at an altitude of 415 m (Fig. 2). This discovery was made while sifting leaf litter on rocky terrain approximately 2.5 km from the international port of Herceg Novi.

Fig. 1

Xylosandrus compactus female found near the village of Kameno in Montenegro in 2023. Lateral view (a), dorsal view (b). Length 1.77 mm

Fig. 2

The location near the village of Kameno with a view of the international port of Herceg Novi (a), interior (b), and a rocky area in an oak-hornbeam forest (c), where one female Xylosandrus compactus was found in November 2023

The nearest known population of X. compactus is on Lokrum Island, Croatia, approximately 40 km from the study site (Pernek et al. 2025). The flight capacity of X. compactus extends up to approximately 8 km per season but may be constrained by altitudes around 400 m above sea level (Gugliuzzo et al. 2019a). It is possible that the observed female specimen was introduced via the international port of Herceg Novi and subsequently dispersed to the recorded location (Fig. 2). At the study site, the beetle may have burrowed into the leaf litter to overwinter. However, it is more likely that this specimen represents an overwintering offspring of a locally developed generation, suggesting a potential establishment of the species in the area. Although no specific searches for galleries were conducted, their presence at the site remains a possibility.

Some ambrosia beetles do not overwinter within their galleries; instead, part of the new generation may leave them and overwinter elsewhere (Hadorn 1933; Swaine 1933; Kinghorn and Chapman 1959). However, this behavior is not consistent across all species (Ranger et al. 2016; Gugliuzzo et al. 2020). For example, in Xylosandrus germanus (Blandford, 1894) and Xylosandrus crassiusculus (Motschulsky, 1866), not all females overwinter within their burrows (Hoffmann 1941; Oliver and Mannion 2001), with some individuals documented overwintering outside galleries. Similarly, the discovery of a single dormant X. compactus female in leaf litter strongly suggests that this species is also capable of overwintering outside its galleries under certain conditions. Given that galleries were not specifically searched for at the site, their potential presence raises the possibility of an already established population in the region.

The detection of a single individual, even without confirmed galleries in host trees, suggests the establishment of a permanent population in the region (see Knížek 2009; Fiala et al. 2021). Nonetheless, to confirm the establishment of X. compactus further surveys are necessary. Montenegro hosts Mediterranean biotopes similar to those along the Italian coast, where the species is already established. Consequently, there is a high likelihood that Montenegro could experience similar damage, particularly to shrubs, as observed in Italy (Pennacchio et al. 2012; Vannini et al. 2017; Gugliuzzo et al. 2019a).

In 2023, the species was also recorded in multiple other European countries, including Slovenia, Russia, Switzerland, and Croatia (Blaser et al. 2024; Hauptman et al. 2024; Karpun et al. 2024; Pernek et al. 2025). This trend indicates a broader and potentially synchronized expansion of this invasive beetle across southern and central Europe.