Ips duplicatus (Sahlberg, 1836), Xylosandrus germanus (Blandford, 1894) and Neoclytus acuminatus (Fabricius, 1775) are invasive species reported in Romania, but their current distribution is poorly known. The research aim was to provide new information on this issue. A survey was conducted over the period 2015–2017 in 82 locations, using flight-interception traps and bottle traps, baited with different attractants. Data obtained in our other unpublished studies were also taken into account. A total of 35,136 I. duplicatus beetles were collected in 30 survey locations. The highest captures were in the log yards of some factories processing logs of Norway spruce (Picea abies (L.) H. Karst.). Considering all known records so far, most of these are in the eastern part of Romania, where an outbreak took place during the years 2005–2014, mainly in spruce stands growing outside their natural range. During the survey, 4259 specimens of X. germanus were collected in 35 locations, but in our other studies the species was found in 13 additional places. It was collected at altitudes of 18–1200 m, and the largest catches were from beech stands, growing at 450–950 m. N. acuminatus was found in only six locations, in the western and southern parts of the country, at low altitudes, in tree stands composed of Fraxinus excelsior L., Quercus spp. and other broadleaf species, as well as in broadleaf log yards. The results suggest that I. duplicatus is established in most parts of the Norway spruce’s range, X. germanus is still spreading in the country, with some areas having quite high populations, while N. acuminatus is present only in the warmest regions of the country.

Natural forests have unique, very stable structures and host a large number of endemic species, making them of high conservation value. The Șinca Old-Growth Forest in Brasov County (Romania) is no exception, being a flagship natural forest of mixed beech and silver fir among European mountain forests. Knowledge of the diversity of beetles living in this ecosystem and of the conservation degree of the species can be obtained by comparing it with the diversity existing in a managed forest, similar in composition and structure. Thus, the present study allowed a first analysis of the terrestrial coleopteran communities captured in pitfall traps both in a forest reserve and in a managed forest. The abundance of captured beetles was about 17% higher in the forest reserve (16,393 individuals) than in the managed forest (14,008 individuals), while species richness was higher in the managed forest (44 species), where 19.1% more taxa were identified than in the forest reserve (37 species). There were significant differences between the two beetle communities indicated via a PERMANOVA test; these differences are most likely due to the presence of certain beetle species only in a certain stand type, but also due to large differences between populations of common insect species. Analyses of the Shannon, Simpson, Evenness, and Berger–Parker diversity indices showed a similar diversity between the two terrestrial beetle communities. The presence of rare species such as Carabus variolosus (Fabricius, 1787), Ceruchus chrysomelinus (Hochenwarth, 1785), and Rhysodes sulcatus (Fabricius, 1787) indicates the high value of this ecosystem and illustrates the importance of its conservation. A more in-depth analysis of beetle diversity in the Șinca forest may only be possible after further research based on additional beetle sampling methods capable of capturing dead wood-dependent insects in particular.

Ips typographus Linnaeus, 1758, the most important pest of Norway spruce (Picea abies Linnaeus, 1753) from Eurasia has damaged, in the last decades, a large area of forest in Romania. Associations between beetles and their symbiotic fungi are well known compared to beetle-mite relationships. The objectives of the study are to determine: (i) the diversity of mites species associated with I. typographus in a local outbreak from Central Romania; (ii) the mite’s preferences concerning the body parts of their carriers; and (iii) how phoresy changes during seasonal flight activity of the host. A total of 7896 adult I. typographus were analyzed and six mite species (both adults and immature stages) were found: Dendrolaelaps quadrisetus Berlese,1920, Proctolaelaps fiseri Samsinak, 1960, Trichouropoda polytricha Vitzthum, 1923, Histiostoma piceae Scheucher, 1957, Uroobovella ipidis Vitzthum, 1923, and Uroobovella vinicolora Vitzthum, 1926. Most mites were observed under the carriers’ elytra (46.8%), while 26.7% and 25.8% were seen on the thorax and elytral declivities, respectively. Mite phoresy peaked in the spring corresponding to the dispersal flight of the carrier. A smaller peak in phoresy occurred in the summer during the second beetle generation.

Trypodendron laeve Eggers, 1939 is a species of ambrosia beetle much less known than the other three Trypodendron species occurring in Europe. Its status (native or alien) in Central Europe has been a subject of debate over the past two decades. In Romania, the species was discovered in 2008 and the aim of the research presented in this paper was to investigate its distribution in the Carpathians, mainly at high altitudes (>800 m), in tree stands with Norway spruce (Picea abies [L.] H. Karst). Panel intercept traps baited with synthetic pheromone for Trypodendron lineatum (Olivier, 1795) were used in the spring of 2015, at 31 locations. Adults of T. laeve were caught in 20 of them. Additional observations were made within some studies using similar baits and T. laeve specimens were caught in eight locations. T. laeve was always trapped together with T. lineatum, and at some locations also together with T. domesticum (Linnaeus, 1758) and T. signatum (Fabricius, 1787). In all traps, fewer specimens of T. laeve were caught compared to T. lineatum. The species has a widespread distribution in the mountain regions, within forests composed of native tree species and generally located far away from commercial routes. There, it occurs together with other native species of the same taxonomic genus. It seems to be more abundant at high altitudes, but overall its populations are less abundant than those of T. lineatum.

The increasing worldwide interest in renewable energy and carbon storage has led to the development of relatively fast solutions to obtain wood biomass. The cultivation of fast-growing tree species in short-rotation crops, such as hybrid poplar clones, is one such solution, at least in temperate areas. Sometimes these monocultures are affected by disturbing factors, including severe insect defoliation, with strong destructive effects. The impact of defoliation on the growth and productivity of poplar crops is often estimated in the context of artificial defoliation. There have been few studies in which the effect of defoliation was calculated after natural defoliation. Among defoliating insect species, Clostera anastomosis L. is one of the most important defoliators of young poplars. This species developed severe defoliation in a 4-year-old poplar clone AF8 crop, from the northeastern part of Romania, in the spring and summer of 2017. The study aimed to assess the impact of defoliation both on the growth and mortality of defoliated trees and the productivity of the affected crop. To reach this goal, the height and radial growth of 150 trees with different defoliation rates (50 non-defoliated, 50 partially defoliated, and 50 completely defoliated) were measured and the defoliation symptoms and mortality were also evaluated for 4780 poplars (10% of the analyzed population). The defoliation caused a significant decrease in the annual height growth (28.6% of the partially defoliated trees and 38.5% of the completely defoliated trees) and a severe decrease in the radial growth, between 82.2% and 90.4%, respectively, depending on the defoliation rate. These strong decreases led to a significant decline in tree-level biomass accumulation, approximately 74.8% for partially defoliated trees and 83.1% for completely defoliated trees, for the year of defoliation. As a result, the loss in total biomass (for the four years of the rotation) was between 28.1% and 34.6%, respectively, depending on the defoliation rate. Therefore, the total biomass loss was 5 t·ha⁻¹, representing approximately 70% of the forecasted production for 2017 only (approximately 7 t·ha⁻¹).

European spruce bark beetle Ips typographus (Linnaeus 1758) (Scolytinae) is considered the most destructive and aggressive pest of Norway spruce in Europe. Recently, Ips duplicatus (Sahlberg 1836) (Scolytinae), another species of bark beetle, that also affects Picea trees, has expanded its range westwards in Europe. In spruce stands, bark beetle populations are closely associated with various organisms such as fungi, nematodes, and mites. While phoretic mites and their relationship with I. typographus have been extensively studied in Europe, only single study has focused on the populations of phoretic mites associated with I. duplicatus. The aim of this study is to analyze and document the communities of phoretic mites and their complex relationships with these two bark beetles species. The research was conducted in a stand located at the lower limit of spruce, where the two pest species have developed outbreaks together. Over 50,000 beetles were collected using wing-type pheromone traps, of which 4,348 were analyzed for the determination of phoretic mites (2,413 I. typographus; 1,935 I. duplicatus). In total, nine species of phoretic mites were identified, of which only six were found on Ips duplicatus. Among the nine species, Dendrolaelaps disetus Hirschmann, 1960 (Digamasellidae), Elattoma sp. (Pygmephoridae), and Paraleius leontonychus Berlese, 1910 (Oribatulidae) are reported for the first time in Romania. The results showed that although Ips typographus beetles carried significantly more phoretic mites than Ips duplicatus throughout the entire flight period, both species exhibited similar peaks in phoresy rate. ONE-WAY PERMANOVA test revealed significant differences between the two phoretic mite communities, differences also highlighted by diversity indices. These differences are most likely due to the presence of certain mite species only on I. typographus beetles, as well as differences between the populations of common species. The phoretic attachment location on host beetles varied across mite and host beetle species.