Assessment of the harmfulness of the main pine trunk pests in Belarus

Mass dieback of pine forests is a direct hit to the forestry economy. During the outbreak of stem pests in 2016–2021, it was necessary to urgently harvest 38.1 million m³ of damaged timber in the forests of Belarus. The main culprit of the dieback at that time was the pine shoot beetle (Ips acuminatus). However, since 2021, the structure of the outbreaks has been changing: the blue pine borer (Phaenops cyanea) is coming to the fore, and its harmfulness continues to grow.

• Timber losses in 2016–2021 — 38.1 million m³
• Field observation period — 2017–2023
• Critical harmfulness threshold — 80 points

To develop effective protection measures, a forest pathologist needs an accurate assessment of the harmfulness of each xylophagous species. All stem insects are divided into four groups according to the type of damage caused. Some species attack weakened and externally healthy trees, killing them. Others damage the wood itself with galleries, reducing its grade. Still others combine both forms of damage, while the fourth group colonizes only dead wood and does not cause economic harm.

Outbreak pests of pine: who needs to be controlled first

During long-term observations in the pine stands of Belarus, the biology and harmfulness of the main xylophages forming dieback foci were assessed in detail. Monitoring was carried out both on model trees and on trap material — unbarked timber, trap trees, and logging residues. The following insect species were studied in field trials:

• pine shoot beetle (Ips acuminatus Gyll.) and six-toothed bark beetle (I. sexdentatus Boern.);
• large (Tomicus piniperda L.) and lesser (T. minor Hart.) pine shoot beetles;
• blue pine borer (Phaenops cyanea F.);
• pine bark weevil (Pissodes piniphilus Hrbst.);
• black pine sawyer (Monochamus galloprovincialis Ol.).

Threat assessment methodology: from physiology to timber quality

To compare the actual damage from species with different biology, a comprehensive scoring system is applied. It takes into account the physiological weakening of the tree, technical destruction of the trunk, and the pest's reproduction rate. The final potential harmfulness is calculated as the product of physiological and technical harmfulness points, multiplied by the number of insect generations per year.

Physiological harmfulness is comprised of points for the activity of the xylophage, the specifics of its supplementary feeding, and its ability to transmit dangerous pathogens. Technical harmfulness is defined as the product of points for the nature of wood destruction by galleries, the site of colonization on the trunk, and the value of the damaged tree species. When calculating galleries, their penetration depth, diameter, and the area of damage under the bark are taken into account.

The site of colonization is evaluated by commodity structure: damage to the butt part of the trunk, which provides large commercial timber, causes maximum economic damage. The value of pine is compared with the stumpage value of aspen. As a result of the calculations, each pest species falls into one of four categories, which determine the necessity and urgency of protective treatments.

E.G. Mozolevskaya recommends assigning 10 points for the physiological activity of stem insects that attack trees of category I (no signs of weakening) and II (weakened) and are capable of mass reproduction in stands with impaired vitality (class II biological stability).

For species colonizing trees of category III (severely weakened) and IV (dying), fresh windfallen wood, and timber in fresh clearings, and forming foci in stands of biological stability class III (having lost vitality), the same criterion is assessed at 1 point. The physiological activity of xylophages whose food base is dead wood corresponds to a score of 0.1.

Thus, the pine shoot beetle and six-toothed bark beetle, large and lesser pine shoot beetles, blue pine borer, and pine bark weevil are capable of colonizing trees of state categories I and II. I. acuminatus, which until recently in Belarus was mentioned as a secondary species in stem pest entomo-complexes and reproduced in weakened resin-tapped pine stands, as well as in stands affected by resin-top disease, in 2016–2017 reproduced in masses and began to attack quite viable pine stands. I. sexdentatus, T. piniperda, T. minor, and Ph. cyanea especially often form foci in stands along the edges of "gaps" affected by variegated root rot of pine, caused by the root sponge (Heterobasidion annosum (Fr.) Bref.). Ph. cyanea foci in Belarus are formed in mature sparse stands along forest edges and clear-cut boundaries, i.e., in places with the highest insolation. P. piniphilus and M. galloprovincialis do not form independent foci in the conditions of Belarus and mainly colonize trees together with the pine shoot beetle, six-toothed bark beetle, and blue pine borer.

E.G. Mozolevskaya suggests rating the ability of species to cause significant damage during supplementary feeding with 2 points, barely perceptible damage with 1 point, and harmless species with 0 points. In this case, the greatest damage is caused by the black pine sawyer and the pine shoot beetle, which feed on shoots and branches (small trunks), and by pine shoot beetles, which carry out "pruning" (tunnelling) of shoots. During supplementary feeding, I. acuminatus and I. sexdentatus bore galleries under the bark of dying trees, and Ph. cyanea feeds on pine needles.

Stem pests associated with pathogens of vascular and necrosis-cancerous diseases are recommended to be rated with 3 points, wood-destroying and wood-staining fungi with 2 and 1 points, respectively. Among the species mentioned above, M. galloprovincialis contributes to the development of stem rots, while other xylophages are vectors of sapwood fungal stains. Furthermore, for the sharp-dentated bark beetle, for example, it has been proven that associated pathogens help to significantly weaken the tree's resistance and overcome its defenses.

The general assessment of the physiological harmfulness of stem pests is presented in the table.

Based on the depth of gallery penetration into roundwood, xylophages were divided into 3 groups: causing surface wormholes (depth up to 3 mm); shallow wormholes (no more than 15 mm); and deep wormholes (more than 15 mm). In accordance with existing documents on the presence of wormholes characteristic of specific xylophage species, the grade and cost of 1 m3 of timber were established.

When timber transitions from one grade to another, the price of 1 m3 of round coniferous timber with a diameter of 14–25 cm decreases compared to grade A: for grade B – by 1.2 times, for grade C – by 1.5 times, and for grade D – by 2.1 times. Grade D includes technological raw materials and firewood.

Table – Assessment of the harmfulness of stem pests of Scots pine

PH criteria TH criteria

Family, species PH TH total OH xylophage PA DDP AB DRP GWA RRP HP generations Curculionidae 1. Sharp-dentated

10 1 1 12 1.5 0.2 1.4 2 4.8 2.5 144.0 bark beetle (Ips acuminatus Gyll.) 2. Six-toothed bark beetle (I. sexdentatus 10 1 1 12 1.5 0.3 1.9 2 6.8 2.5 204.0 Boern.) 3. Common pine shoot beetle (Tomicus 10 2 1 13 1.5 0.1 1.9 2 6.1 1.0 79.3 piniperda L.) 4. Lesser pine shoot beetle (Tomicus 10 2 1 13 1.5 0.1 1.4 2 4.5 1.0 58.5 minor Hart.) 5. Pine shoot beetle

10 2 1 13 1.5 0.1 1.4 2 4.5 1.0 58.5 (Pissodes piniphilus Hrbst.) Buprestidae 6. Blue pine borer

10 1 1 12 1.5 0.1 1.9 2 6.1 1.0 73.2 (Phaenops cyanea F.) Cerambycidae 7. Black pine sawyer

10 2 2 14 2.1 0.3 1.9 2 9.1 1.0 127.4 (Monochamus galloprovincialis Ol.) Note. PH – physiological harmfulness; PA – physiological activity; DDP – ability of species to cause damage during supplementary feeding; AB – ability to carry pathogens; TH – technical harmfulness; GWA – gallery wood-destruction depth; DRP – depth replenishment parameter; RRP – region of residence on the tree; HP – host plant; OH – overall harmfulness.

We accept these figures as initial coefficients characterizing the depth of wood destruction. Insect damage in pine timber is not permitted in grades A and B. Shallow wormholes are permitted in grade C roundwood – less than 2 mm in diameter and up to 15 mm in depth, and 2 mm or more in diameter and up to 5 mm in depth. In grade D timber, wormholes with a diameter of up to 2 mm are allowed; if they are 2 mm or more, only initial stages of bark beetle infestation are permitted.

For species creating large (over 0.3 cm in diameter), medium-sized surface (1–2 dm2) galleries, or galleries penetrating 10–20 cm into the wood, the addition is 0.1 points. For xylophages whose surface galleries cover an area of more than 2 dm2 or penetrate deep into the wood and are over 20 cm long, we add 0.2 points.

Thus, the character of wood destruction by galleries will be:

– for the sharp-dentated bark beetle 1.5 + 0.1 + 0.1 = 1.7;

– six-toothed bark beetle 1.5 + 0.1 + 0.2 = 1.8;

– common pine shoot beetle 1.5 + 0.1 = 1.6;

– lesser pine shoot beetle 1.5 + 0.1 = 1.6;

– pine shoot beetle 1.5 + 0.1 = 1.6;

– blue pine borer 1.5 + 0.1 = 1.6;

– black pine sawyer 2.1 + 0.1 + 0.2 = 2.4.

To assess the region of residence of stem pests, we take the estimation coefficient for small grade B timber as 1 and calculate the coefficients for medium (1.4) and large (1.9) timber. We determine the classification of individual species into one of the groups based on their most harmful capability.

When assessing the harmfulness of stem pests, E.G. Mozolevskaya uses a coefficient characterizing the value of pine wood equal to 2. This factor depends on the market price of wood, and when we compare the harmfulness of different pests for one crop, this factor is not of fundamental importance.

The number of generations per year is taken into account at the final stage of determining harmfulness. With multiple generations, insect harmfulness increases. The coefficient proportionally changing the harmfulness assessment score based on the generation is:

• for species capable of producing two generations – 2.0;
• sister generations – 1.5;
• having a biennial generation – 0.5.

According to our research, an annual generation is characteristic of T. piniperda, T. minor and Ph. cyanea, P. piniphilus and M. galloprovincialis. Such bark beetles as I. acuminatus and I. sexdentatus form two generations per year, with parent beetles laying eggs at least twice.

The total pest damage scores we calculated for seven species of stem pests are presented in the table:

It should also be noted that E.G. Mozolevskaya's methodology did not account for the ability of aggressive xylophages to successfully reproduce in clearings, thereby increasing their population, which we have recorded multiple times. Therefore, if necessary, the total damage score for species developing on logging residues can be adjusted. For example, for stem pests that colonize large logging residues – stumps, trunk sections, or smaller ones – branches, which are produced in large quantities after logging and are successfully exploited by pests.

For the first time in Belarus, an assessment of the damage caused by the seven most significant xylophages of pine stands has been conducted. Among the representatives of three families of stem pests, the six-toothed bark beetle has the highest damage score (204.0 points), belonging to the group of highly destructive xylophages, which also includes the pine shoot beetle (144.0) and the black pine sawyer (127.4). The damage caused by I. sexdentatus and I. acuminatus is primarily due to the double generation and the presence of sister generations, and in the case of M. galloprovincialis, due to maximum physiological and technical damage.

The group of moderately damaging species is represented by the large (79.3) and lesser (58.5) pine shoot beetles, the blue pine buprestid (73.2), and the pine weevil (Pissodes piniphilus) (58.5).

Regarding the insects of these two groups, it is mandatory to organize and conduct forest pathological monitoring and sanitary-preventive measures (clear and selective sanitary logging, removal of logging debris) aimed at regulating the population of xylophages, which is not practical to plan against minor or harmless species. Such an assessment is important when determining the degree of significance of stem pests, taking into account their occurrence and substantiating protective measures in pine stands.

Sautkin, F. V. Experience in assessing the level of damage caused by leaf miners – pests of ornamental shrubs in green spaces of Belarus / F. V. Sautkin, S. I. Evdoshenko, S. V. Buga // Plant Protection: collection of scientific papers / Scientific and Practical Center of the NAS of Belarus for Agriculture, Institute of Plant Protection; editorial board: L. I. Trepashko (editor-in-chief) [et al.]. – Nesvizh, 2012. – Issue 36. – P. 198–210.

Sautkin, F. V. Assessment of the level of damage caused by Phyllonorycter robiniella (Clemens, 1859) – a pest of black locust (Robinia pseudoacacia L., 1753) in the conditions of green spaces in different regions of plant introduction in Belarus / F. V. Sautkin, F. V. Sinchuk // Proceedings of the Belarusian State University. Physiological, biochemical and molecular foundations of biosystem functioning. – 2014. – Vol. 9, part 2. – P. 110–115.

Petrov, D. L. Comprehensive assessment of the level of damage caused by gall-forming aphids in ornamental tree stands / D. L. Petrov, S. V. Buga // Plant Protection: collection of scientific papers / Scientific and Practical Center of the NAS of Belarus for Agriculture, Institute of Plant Protection; editorial board: L. I. Trepashko (editor-in-chief) [et al.]. – Nesvizh, 2008. – Issue 32. – P. 305–315.

Mozolevskaya, E. G. Assessment of the damage caused by stem pests / E. G. Mozolevskaya // Issues of forest protection: collection of scientific papers / Moscow Forest Engineering Institute; editorial board: A. I. Vorontsov (executive editor) [et al.]. – M., 1974. – Issue 65. – P. 124–132.

Meshkova, V. L. Damage caused by xylobionts in oak clearings in Left-bank Ukraine / V. L. Meshkova, O. N. Kukina // Bulletin of St. Petersburg State Forest Technical Academy. – 2011. – Issue 196. – P. 238–246.

The blue pine buprestid (Phaenops cyanea (Fabricius, 1775)) – a new threat to the forests of Belarus / A. A. Sazonov [et al.] // Proceedings of BSTU. Ser. 1. Forestry, Nature Management and Processing of Renewable Resources. – 2023. – No. 1 (264). – P. 61–72.

Methodological recommendations for the surveillance, accounting, and forecasting of mass outbreaks of stem pests and the sanitary condition of forests / Ministry of Natural Resources of the Russian Federation, Federal Forestry Agency, VNIILM; developed by A. D. Maslov. – Pushkino, Moscow region: VNIILM, 2006. – 108 p.

Ryvkin, B. U. Infestation of BSSR forests by pests (based on data from the 1930 forest entomological survey) / B. U. Ryvkin. – Minsk: Selkhozsektor, 1933. – 63 p.

Stark, V. N. Fauna of the USSR. Coleoptera / V. N. Stark. – M., L.: USSR Academy of Sciences, 1952. – Vol. XXXI. Bark beetles. – 463 p.

Kharitonova, N. Z. Specifics of damage to pine by xylophagous insects in root rot centers / N. Z. Kharitonova, N. G. Dushin // Modern problems of forest protection and ways to solve them: materials of the regional scientific-production conference of Belarus and the Baltic republics (Minsk, Sept. 13–15, 1984) / Western Department of VASKHNIL, Belarusian Technological Institute named after S. M. Kirov; editorial board: N. I. Fyodorov (editor-in-chief) [et al.]. – Minsk, 1985. – P. 122–123.

21. Davydenko, K. Fungi associated with Ips acuminatus (Coleoptera: Curculionidae) in Ukraine with a special emphasis on pathogenicity of ophiostomatoid species / K. Davydenko, R. Vasaitis, A. Menkis // European J. of Entomology. – 2017. – Vol. 114, № 1. – Р. 77–85.

Rechitsa Experimental Forestry [Electronic resource]. – Access mode: http://rechicales.by. – Access date: 30.10.2023.

Kukhta, V. N. Features of the development of the sharp-dent bark beetle (Ips acuminatus (Gyllenhal, 1827) Coleoptera: Curculionidae, Scolytinae) in pine forests of Belarus / V. N. Kukhta, A. A. Sazonov // Pine forests: current state, existing problems and ways to solve them: materials of the International scientific and practical conference (Kyiv, June 12–13, 2019) / NAS of Ukraine; editorial board: V. Tkach [et al.]. – Kyiv, 2019. – P. 54–61.

Kukhta, V. N. Use of logging residues as trap material in pine forests / V. N. Kukhta, A. A. Sazonov, D. A. Babul // Proceedings of BSTU. Ser. 1. Forestry, Nature Management and Processing of Renewable Resources. – 2020. – No. 2 (234). – P. 100–108.

V. N. Kukhta Belarusian State Technological University, Minsk

COMPARATIVE ASSESSMENT OF THE

HARMFULNESS OF SCOTTS PINE

Annotation. The article provides an assessment of the harmfulness of 7 species of stem pests that form centers of mass reproduction in the pine forests of Belarus. The overall harmfulness of xylophages varied from 58.5 to 204.0 points. The group of particularly harmful species includes Ips sexdentatus (Boern.), Ips acuminatus (Gyll.) and Monochamus galloprovincialis (Ol.), moderately harmful species include Tomicus piniperda (L.), Tomicus minor (Hart.), Pissodes piniphilus (Hrbst.), Phaenops cyanea (F.) Based on harmfulness indicators, mandatory organization and implementation of forest protection measures against these pests are proposed.

Key words: xylophages, harmfulness, pine stands.