Introduction Recently, in pine forests of many regions, the outbreak of bark beetles, particularly Ips sexdentatus (B?rner, 1776) (Coleoptera: Curculionidae: Scolytinae) have been registered. Prevention of outbreaks and decrease of the negative consequences for forest can be achieved by the use of fertilizers, insecticides, and entomophages. Thanasimus formicarius (Linnaeus 1758) (Coleoptera: Cleridae) is a predator of many coleopterous species. The aim of the research was to evaluate the first results of the release of Th. formicarius into the foci of bark beetles. Materials and Methods The study was carried out in the foci of bark beetles in Kharkiv, Sumy, and Chernigiv regions. The larvae of Th. formicarius were reared in the State Specialized Forest Protection Enterprise ‘Kharkivlisozahyst’. After that, they were moved to the forest and released. The experiment was carried out with five variants of application the fertilizer and predator, one variant of predator release without fertilizer, one variant of the fertilizer ‘Iaros’ treatment without predator release, and one variant without any treatment. The control plots were of three types: K-1 – release of predator larvae without applying a fertilizer; K-2 – treatment with fertilizer without the release of predator; K-3 – without treatment with fertilizer and without the release of predator. The change in the health condition of trees and bark beetles’ survival were the criteria for evaluating the treatment effectiveness. Results and Conclusions The efficiency of different combinations of treatment with fertilizer and the release of the predator, evaluated by the change of the health condition of viable trees, was from 14.7 to 28.3%. According to the 2020 assessment, the density of larval galleries of the bark beetle decreased in all plots compared to 2018. The more rapid collapse of bark beetle outbreak as compared to the control was registered for the plots with predator release. The release of the predator along with the use of mineral fertilizer by spraying the crowns provided a more significant improvement in the stand health condition and a decrease in the viability of the bark beetle populations than the only predator release.

The purpose of this study was to identify the species composition of coleopterous predators and their occurrence in different parts of the stem depending on the health condition of Scots pine (Pinus sylvestris L.) in the collapsing foci of bark beetles (Coleoptera: Curculionidae: Scolytinae). The research was carried out in 2019–2021 at 38 sample plots located in five State Forestry Enterprises of Sumy region (Ukraine). All sample plots are located in pure Scots pine stands in relatively poor forest site conditions. The relative density of stocking is 0.6–0.7, and the age of stands is between 60 and 110 years. The health condition for each tree was evaluated on visual characteristics by the classes: first – healthy; second – weakened; third – severely weakened; fourth – drying up; fifth – recently died and sixth – died over a year ago. Bark beetles’ nuptial chambers and predators were counted on 25 × 25 cm pallets, which were located at the lower, middle and upper parts of the stem with thin, thick and transitional bark, respectively. The significance of differences in the performance of predator species depending on the tree part, health condition and year was analysed using the nonparametric Kruskal–Wallis (K–W) test. The species composition of predators in different years, stem parts and tree health condition was compared using the Sorensen–Chekanovsky index. In the collapsing foci of bark beetles, the health condition of Scots pine in 2019–2021 tended to worsen. The infestation density of Ips acuminatus (Gyllenhal, 1827) and Ips sexdentatus (Boerner, 1767) was 0.62 ± 0.032 and 0.64 ± 0.017 nuptial chambers per 1 dm2, respectively, and also decreased in 2019–2021. In the galleries of bark beetles, seven species of coleopterous predators were collected: Aulonium ruficorne (Olivier, 1790) (Zopheridae), Platysoma elongatum (Leach, 1817) (Histeridae), Rhizophagus depressus (Fabricius, 1792) (Monotomidae), Corticeus pini (Panzer, 1799) (Tenebrionidae), Thanasimus formicarius (Linnaeus, 1758), Thanasimus femoralis (Zetterstedt, 1828) (Cleridae) and Salpingus ruficollis (Linnaeus, 1761) (Salpingidae). Two more species – Glischrochilus quadripunctatus (Linnaeus, 1758) (Nitidulidae) and Pytho depressus (Linnaeus, 1767) (Pythidae) – were singly collected in the foci. T. formicarius and P. elongatum were the most abundant. The ratio of predator–prey significantly increased from the upper to the lower part of the stem with thick bark. It, however, decreased in this stem part from the fourth to the sixth class of the health condition of the host tree.