THE FIRST RESULTS OF THE BIOLOGICAL CONTROL OF IPS SEXDENTATUS USING THANASIMUS FORMICARIUS IN UKRAINE

Thanasimus formicarius (Linnaeus 1758) (Coleoptera: Cleridae) is a predator of many coleopterous species. In 2018, the rearing of this predator started in the State Specialized Forest Protection Enterprise ‘Kharkivlisozahyst’. The aim of this research was to evaluate the first results of the release of Th. formicarius to prevent the bark beetle spreading. The experiment was carried out with five variants of application of the fertilizer and predator, one variant of predator release without fertilizer, one variant of fertilizer treatment without predator release, and one variant without any treatment. 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 together 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 bark beetle populations than the only predator release. K e y w o r d s : bark beetle; predator, health condition index, density of larval galleries, density of exit holes.

The control plots were of three types: K-1release of predator larvae without applying the fertilizer; K-2fertilizer treatment without the release of predator; K-3without fertilizer treatment and without the release of predator (Table 1). The changes in the health condition of trees and bark beetles' survival were the criteria for evaluating the effectiveness of the treatment. The assessment of both the health condition of trees and survival of bark beetle larvae were carried out in each variant in five replicatesin randomly selected fragments within the treated plots. Since the trees of the 5 th and 6 th categories of health condition in the stands were used for the predator release, the effect of the treatment was assessed by changing the health condition index of viable trees (1 st -4 th categories) and by the proportion of the trees of the 1 st -3 rd categories for the period from 2018 to 2020.
In July 2018 and 2020, the average number of larval galleries of Ips sexdentatus and a number of the larvae that successfully completed development were assessed, and then a proportion of the individuals that successfully completed development was calculated on the model trees of the experimental and control plots.
The effect of the treatment was estimated by the Formula 1: where K 0 and K ithe values in the control plot (K-3) in 2018 and 2020, respectively, P 0 and P ithe values in the experimental (treated) plots in 2018 and 2020, respectively.
Summary statistics, one-way analysis of variance (ANOVA), and Tukey HSD test with a significance level of p < 0.05 were performed (Atramentova & Utevskaya 2008). Microsoft Excel software and statistical software package PAST: Paleontological Statistics Software Package for Education and Data Analysis (Hammer et al. 2001) were used.
Results and Discussion. The analysis of the survey data in 2018 did not reveal any significant differences in the category of the health condition of viable trees in the plots of different variants (Table 2). In 2020, the health condition of the trees improved in V-1-V-5, while it worsened in K-1-K-3. It must have happened due to the fact that the predator increased its number in favourable conditions and effectively reduced the population of bark beetles.
The efficiency of different combinations of the fertilizer treatment and a release of the predator, evaluated by the change in the health condition of viable trees, made from 14.7% in V-5 to 28.3% in V-1 ( Table 2).
The highest efficiency of V-1-V-3 may be connected with the summer treatment in the year when the bark beetles outbreak started to go down (in 2018). The health condition of the stands significantly improved in those three variants, and insignificantly in V-4 (the fertilizer treatment in September) and did not change in V-5 with the fertilizer treatment in October 2018.
The measures taken contributed to the fact that the health condition of the stands ceased to deteriorate. The dead trees fell out of the stand composition, however, further deterioration of the health condition of the stand went on. The obtained conclusion is supported by a comparison of the proportion of trees of the 1 st -3 rd categories of health condition in different variants (Fig. 1). For two years, the proportion of such trees in most of the experimental plots increased, it changed insignificantly in V-5, and decreased in the control. However, a significant improvement in this indicator was noted only in V-1, which can be associated with an initial distribution of the trees before the start of the experiment. However, in V-4 (the fertilizer treatment and release of predator larvae were carried out in September 2018) the proportion of the trees of the 1 st -3 rd categories was the lowest in 2018 and it increased by 1.2 times (by contrast, by 1.5 times in V-1, by 1.1 and 1 times in V-2 and V-3, respectively, and 1.1 times in V-5). The proportion of viable trees for two years significantly decreased in the control plots (1.7, 2.3, and 2.8 times in K-1, K-2, K-3, respectively).  Table 1) by assessment of 2018 and 2020. Values followed by different letters are significantly different at the 95 % confidence level In 2018, the density of I. sexdentatus population in all plots exceeded 3 larval galleries /dm 2 ( Table 3). The value was above the middle level for this species in V-1, K-1, and K-3 (4 larval galleries /dm 2 -Methodical recommendations 2010). From 62.5 to 89.7% of larvae successfully completed development in 2018, particularly 78.6-89.5% in V-1-V-5, 84% and 78.3% in K-1 and K-2, respectively, and 89.7% in K-3. According to the 2020 assessment, the density of larval galleries of the bark beetle decreased in all plots compared to 2018 (Table 4). It is consistent with the data on the collapse of the outbreak. At the same time, in the variants of the experiment, this value decreased by 2.1-1.5 times in V-1-V-5 and by 1.5 times in the K-1-K-2. In K-3 it decreased by 1.4 and remained maximal (3.8 galleries / dm 2 ). From 2.57 to 4.17 exit holes / dm 2 were registered n 2018 and from 0.97 to 2.45 exit holes / dm 2 in 2020. These numbers decreased by 3,6-1,9 times in V-1-V-5, by 1.8 times in K-1, by1.3 times in K-2, and by 1.7 times in K-3.
Calculation of the effectiveness of the experiments according to Formula 1 using the characteristics of the health condition of viable trees and the condition of bark beetle population allows us to draw similar conclusions.
The efficiency is significantly higher for the combined use of fertilizer with the introduction of a predator in comparison with the use of these measures separately (Fig. 2). The highest efficiency was obtained in V-1 (28.3% and 32.5% for the health condition of trees and for bark beetles, respectively). However, these results do not statistically differ from V-2 (23.1% and 25.3 %).
The efficiency of the V-4 with the use of fertilizer and the introduction of a predator in September 2018 was significantly less than V-1-V-3 in terms of the health condition of viable trees (18.6%) but did not differ from them in terms of the condition of the bark beetle population (16 %). Therefore, we suggest that a treatment timing does not affect significantly the efficiency while a number of applications does affect it.  Table 1). The data for all inspected stands were pooled for each variant. The values followed by different letters are significantly different at the 95 % confidence level The efficiency of the V-5 with the use of fertilizer in October 2018 and August 2019 and the release of a predator in August 2019 evaluated by tree health condition (14.7%) is significantly lower than in V-1-V-3 and significantly higher than in K-1-K-2, while in K-1 and K-2 the efficiency did not differ significantly. The effectiveness of the measures applied, calculated by the change in the viability of bark beetles, did not significantly differ in V-1-V-4, on the one hand (32.5-16.5%), and V-5-K-1-K2 (5,2-6.4 %), on the other hand. Publications indicate a maximum efficiency of the biological method during the period of outbreak collapse (Kenis et al. 2004, Warzee et al. 2006. At the same time, the increase in the efficiency of predators is facilitated by their repeated release into the pest focus (Zondag 1979). Our first experience with the Th. formicarius release into the focus of Ips sexdentatus in Ukraine showed that the release of predator along with the fertilizer treatment increases the efficiency of forest protection.
The release of predator without additional fertilizer treatment in the stand (K-1), as well as fertilizer use without a release of predator (K-2) provide less efficiency than the joint application of these measures, on average 3.2-5.2 and 3.7-17 times, respectively. Fertilizer treatment and release of a predator in July and twice a year (in July-August and October) turned out to be more effective than in September 2018. Its application in August 2019 was more effective carried out along withfertilization in July than in October 2018 and August 2019. Conclusions.
1. The release of predator Thanasimus formicarius into the focus of bark beetle Ips sexdentatus promotes a more rapid collapse of the outbreak as compared to the control.
2. The release of a predator along with spraying mineral fertilizer on crowns provides a more significant improvement of the stand condition and a decrease in the viability of bark beetle population than the release of a predator only.