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(1) Background: The invasive ambrosia beetle Xylosandrus compactus (Coleoptera, Curculionidae, Scolytinae) poses an increasing risk of being introduced into new environments, mostly unintentionally, via wood products, live plants, and wood packaging materials. It is already spreading across Europe and causing growing concern due to its destructive behavior and by infesting a wide range of woody plants. The aim of this research is to identify X. compactus in Croatia and compile a list of recorded host plants. (2) Methods: Fieldwork was conducted through the assessment of beetle presence and infestation levels on host plants showing visible symptoms of attack, as well as through sampling of the beetles. Adult specimens of bark beetles were examined under a microscope, and molecular analysis was done. DNA was extracted from three randomly chosen individuals. The sequences were compared using the BLAST tool in the NCBI GenBank database. (3) Results and Conclusions: X. compactus was confirmed as a new record in Croatia, infesting laurel (Laurus nobilis), holm oak (Quercus ilex), laurestine (Viburnum tinus), olive (Olea sp.), myrtle (Myrtus communis), strawberry tree (Arbutus unedo), and pittosporum (Pittosporum tobira).

Infestations have persisted following a sudden and intense outbreak of the bark beetle Orthotomicus erosus along the Croatian coast, necessitating a continuous battle against this pest. A recommended protective action is the utilization of pheromone traps for population surveillance. Previous monitoring efforts have recorded an exceptionally high capture rate of natural enemies using pheromone traps; these traps inadvertently prevented natural enemies from fulfilling their essential role in controlling bark beetle populations. To address and significantly diminish instances of this unintended capture, our study designed a modification to the Theysohn-type pheromone trap by integrating a metal mesh within the trapping container. An experimental setup was established in Marjan Forest Park, situated on a peninsula bordered by the sea on three sides and partly by the city of Split. For monitoring purposes, unmodified standard pheromone traps were deployed at the onset of a significant O. erosus outbreak in Croatia in 2018. Catch data from 2020 to 2022 show a marked decrease in the bark beetle population, indicating a shift toward a latent phase. In 2022, modified traps were integrated into the existing monitoring setup, consisting of 10 pairs, to evaluate whether modifications to the traps could significantly reduce the capture of the bark beetle’s natural enemies, specifically Temnoscheila caerulea, Thanasimus formicarius, and Aulonium ruficorne. The objective is to offer recommendations for forestry practices on employing pheromone traps with minimal disturbance to the ecological equilibrium. Our findings indicate that the modifications to the traps markedly decreased the capture of natural predators, particularly T. caerulea, which was the predominant predatory insect found in the traps. Simultaneously, captures of the target species, all bark beetles in the trap, were marginally reduced. This decrease in the capture rates of the target bark beetle species, O. erosus, is not considered problematic when pheromone traps are utilized primarily for monitoring purposes. The modifications to the traps significantly reduced the capture of common bark beetle predators, thereby facilitating a more balanced strategy in forest protection efforts.

The oak lace bug (OLB) Corythucha arcuata (Say, 1832) is an invasive alien species (IAS) that potentially could have many negative impacts on European oak health. Certain measures can be applied to counteract these effects. However, these measures may not be acceptable for forest managers or other stakeholder groups, such as private forest owners, environmental NGOs or the general public. Thereby, we set out to study the perception and knowledge of foresters and other stakeholders on the health status of European oak forests affected by oak lace bug and to investigate what forest health management measures would be acceptable to these target groups. An online survey questionnaire was designed and distributed via social networks, as well as professional networks via e-mails. The survey questionnaire was completed by 2084 respondents from nine European countries: Austria, Croatia, Belgium, France, Hungary, Italy, Romania, Serbia and Slovenia. Even though only a little over 60% of respondents reported they had noticed the discolouration of oak leaves caused by OLB, almost all (93%) considered it to be a problem. As respondents come from a country where C. arcuata is widespread and established, people’s general knowledge and awareness of OLB began to increase. The survey revealed that foresters thought that the insect affected photosynthesis, acorn crop and the aesthetics of the trees, but cannot cause death of trees. However, they assume that the value of the wood would decrease (this fact is also supported by the respondents who are connected to an environmental NGO), but that OLB does not affect property value. However, forest owners claim that the value of the property can be affected and that people would avoid entering the forest. In terms of potential control methods, respondents preferred biological or mechanical measures over chemical ones. We consider this study to be a good basis for further research on the topic of perception, knowledge and attitudes related to OLB since we can expect that the IAS, such as OLB, will certainly spread to European countries that were not included in this survey.

Bark beetle outbreak sites were analysed before sanitary logging in Gorski Kotar County during spring, summer and autumn 2021. Downed European silver fir trees were inspected for red-listed saproxylic entomofauna. Among other species, the fir pinhole borer (Treptoplatypus oxyurus, Dufour, 1843) (Coleoptera: Platypodidae) was observed and studied on-site and in the laboratory. Symptoms of T. oxyurus presence were recognised as white filamentous bites of sawdust on the bark of the fir trees and the surrounding soil. Every tree infested infested with T. oxyurus was measured (diameter at breast height, height/length), and its position was recorded. Segments were collected for laboratory analysis to evaluate the layout and position of T. oxyurus gallery system. The results showed that individual corridors of T. oxyurus, as a rule, never intersect, cross or connect. Each family of beetles (male, female and their offspring) lives separately in its corridor system. There were examples of corridors that were very close to each other but did not touch. T. oxyurus is still completely unknown to forest operatives in Croatia, who do not recognise symptoms of its occurrence.

Boundaries between habitats are usually accompanied by transitions in the diversity and structural complexity of insect assemblages. Edge effects on carabid beetle assemblages across forest-meadow ecotones in Dinaric beech-fir forests were determined in the Gorski Kotar region of western Croatia. Embedded forest edges were greater than 100 years old and had a similar composition and structure of vegetation to that in the adjacent forest. A total of 20,526 individuals belonging to 66 carabid beetle species were recorded. Embedded forest edges reduced the microclimate edge effect by providing stable microclimatic conditions for carabid assemblages similar to those in the forest interior. In addition, this enabled forest specialists and generalists to occur right up to the forest edge and maintain stable populations in the ecotone. This study confirmed that the structure and ages of the vegetation at edges may play a key role in determining the spatial pattern of carabid beetles across forest-meadow ecotones.

We show that the population ecology of the 9‐ to 10‐year cyclic, broadleaf‐defoliating winter moth (Operophtera brumata) and other early‐season geometrids cannot be fully understood on a local scale unless population behaviour is known on a European scale. Qualitative and quantitative data on O. brumata outbreaks were obtained from published sources and previously unpublished material provided by authors of this article. Data cover six decades from the 1950s to the first decade of twenty‐first century and most European countries, giving new information fundamental for the understanding of the population ecology of O. brumata. Analyses on epicentral, regional and continental scales show that in each decade, a wave of O. brumata outbreaks travelled across Europe. On average, the waves moved unidirectionally ESE–WNW, that is, toward the Scandes and the Atlantic. When one wave reached the Atlantic coast after 9–10 years, the next one started in East Europe to travel the same c. 3000 km distance. The average wave speed and wavelength was 330 km year⁻¹ and 3135 km, respectively, the high speed being incongruous with sedentary geometrid populations. A mapping of the wave of the 1990s revealed that this wave travelled in a straight E–W direction. It therefore passed the Scandes diagonally first in the north on its way westward. Within the frame of the Scandes, this caused the illusion that the wave moved N–S. In analogy, outbreaks described previously as moving S–N or occurring contemporaneously along the Scandes were probably the result of continental‐scale waves meeting the Scandes obliquely from the south or in parallel. In the steppe zone of eastern‐most and south‐east Europe, outbreaks of the winter moth did not participate in the waves. Here, broadleaved stands are small and widely separated. This makes the zone hostile to short‐distance dispersal between O. brumata subpopulations and prevents synchronization within meta‐populations. We hypothesize that hostile boundary models, involving reciprocal host–herbivore–enemy reactions at the transition between the steppe and the broadleaved forest zones, offer the best explanation to the origin of outbreak waves. These results have theoretical and practical implications and indicate that multidisciplinary, continentally coordinated studies are essential for an understanding of the spatio‐temporal behaviour of cyclic animal populations.

Many bark and ambrosia beetle species (Coleoptera: Scolytinae and Platypodinae) are known to have spread worldwide in relation to international trade. Concerns have been expressed within the European and Mediterranean Plant Protection Organization (EPPO) about recent introductions of non-indigenous species of these groups. Regulation of the non-coniferous wood trade into many EPPO member countries is currently not sufficient to cover such risks. In 2018–2019, an EPPO study on the risk of bark and ambrosia beetles associated with imported non-coniferous wood was carried out, and the key characteristics contributing to the pest risk from introduced species were determined using expert consensus. This paper summarizes the key findings of the study, which are available in full detail on the EPPO website. The study identified biological and other risk factors and illustrated them with examples from 26 beetle species or groups of species known to be invasive or posing a threat to plant health. These representative species were classified into three categories based on known damage and level of uncertainty. In the present article, factorial discriminant analyses were used to identify features of bark and ambrosia beetle biology associated with damage caused and invasiveness. Based on the information assembled and consideration of the risk factors, it was recommended that in order to prevent the introduction of new bark and ambrosia beetles via non-coniferous wood commodities, horizontal phytosanitary measures should be adopted, irrespective of the host plant species and the origin (i.e., for all genera of non-coniferous woody plants and from all origins). Phytosanitary measures are presented here for various wood commodities.

The aim of this research was to identify pathogens in field populations of the genus Pityokteines from Croatia with special reference to their spatial distribution throughout the country. Pathogens occurrence was studied in 5,968 adult specimens of three silver fir bark beetle species: Pityokteines curvidens, P. spinidens and P. vorontzovi. Four pathogen species were observed in different tissues of their hosts. The pathogens Canningia spinidentis and Menzbieria sp. were found only in P. spinidens, while Chytridiopsis typographi and Gregarina sp. were also present in P. curvidens and P. vorontzovi. Multiple infections were observed in all three beetle species where gregarines occurred together with C. typographi and in combination with C. spinidentis in the specimens of P. spinidens. All pathogen species found in this research are first descriptions on host Pityokteines spp., except Canningia spinidens. Data presented in this study show possible candidates for further tests to utilize pathogens as microbial control agents against fir bark beetles in the future.

Against the background of the phenomenon of globalisation, which has increasingly intensified in recent decades, invasive alien species (IAS) have led to biological invasions that have resulted in multiple negative effects on economies, human health, and especially on the environment. In order to control invasive alien species, preventive actions are considered the most effective methods. In this context, society can actively participate in the process of early detection and preventing the spread of these organisms, but there is a need to raise public awareness. In order for this process to take place in the most efficient way, it is necessary to initially evaluate the knowledge of the general public to IAS. Through a questionnaire that was circulated in ten European countries and had over two thousand respondents, this study aimed to investigate the level of knowledge of some stakeholders in the forestry sector regarding IAS. The results showed that a vast majority of respondents who participated in the study had heard about IAS and provided a correct definition of these organisms. Most of the respondents in this study heard for the first time about IAS from school, the Internet, or journal articles. Data analysis also showed that stakeholders in the forestry sector (foresters, forest owners, and members of environmental NGOs) were more likely than the other respondents to be aware of the impact of IAS. The results of this study offer an insight to researchers and decision makers assessing the differences of opinion regarding invasive alien species, and the necessary steps that could be adopted in the process of raising awareness in society.

The North American gall mite Aceria fraxiniflora was first recorded in Europe in southeast Hungary in 2017. Since then, it has shown a remarkably rapid spread on its host, the also North American green ash (Fraxinus pennsylvanica). By the beginning of 2023 it has been recorded in eight Central-Eastern European countries. In 2022 it was recorded on the other North American ash (Fraxinus Americana) in Zagreb (Croatia) and in Szarvas Arboretum (SE Hungary). Possible reasons and outcomes of this spread are discussed.