UDC 630.4 effect of buds manually removal and their damage by large pine weevil (Hylobius abietis L.) on scots pine seedlings in siversky donets river valley

Large pine weevil (Hylobius abietis L.) damages different organs of Scots pine (Pinus sylvestris L.) seedlings in unclosed plantations, including foliage, buds, stem bark and roots. Simulated damage of respective organs, particularly debudding is one of the ways to evaluate qualitative and quantitative influence of such damage on tree condition. The aim of research was to evaluate the dependence of Scots pine seedlings mortality and height increment on artificial and large pine weevil caused bud damage. The growth of apical shoots of Scots pine seedlings was registered since the beginning of May to the end of June. Development of new shoots in seedlings with manually bud removal or large pine weevil damage started in beginning of May and continued in July. Mortality of Scots pine seedlings with 20 % of lateral buds damaged did not differ from that in undamaged plants. The seedlings with apical and lateral buds manually removed as well as with apical and over 70 % lateral buds damaged by large pine weevil have died in the year of treatment or damage. The seedlings with apical buds damaged as well as with apical and over 50 % lateral buds damaged died in the 4th year after damage. Removal or damage up to 50 % lateral buds did not affect the growth of Scots pine seedlings. Height increment of seedlings with apical buds manually removed or damaged by large pine weevil did not differ significantly in May and June of the year of treatment or damage. In July the height increment was statistically greater in the variant with manually removal of apical bud. Previously suggested scale of Scots pine seedlings bud damage satisfactory reflects the score of large pine weevil injuriousness.


Introduction. Large pine weevil (Hylobius abietis
Linnaeus 1758) is one of the most spread and dangerous pests of conifer plantations, especially in the first years after planting. Its larvae develop under the bark of stumps or roots of weakened trees, and adults damage different parts of trees during maturation feeding (Wainhouse et al., 2004, Nordlander et al., 2017. Such damage is the most dangerous for the Scots pine (Pinus sylvestris L.) transplants of the first three years old, because they have small stem surface, and small number of buds and needles. In the Siversky Donets river valley the large pine weevil depending on weather conditions develops in one or two years. Its swarming, mating, oviposition and maturation feeding occur throughout the summer with two waves. The first wave includes the beetles of hibernating generations of different age (1-3 years old) and is the highest by population number and damage. It starts with beginning of vegetation period (about middle of April), has maximum at the second half of May and the first half of June. The second wave is lower, includes the beetles of the new generation, and begins in July with maximum at the second half of August and the first half of September (Meshkova & Sokolova, 2017).
Attempts are known to evaluate insect injuriousness in different regions with the main aim to substantiate the measures on forest protection (Kulman, 1971, Iyerusalimov, 2004. It was evaluated by crown condition, phytomass of individual organs, radial increment, mortality etc. (Langstrom et al., 1998, Lyytikainen, 1994. To a lesser extent, the changes in stem shape and the associated timber defects were taken into account (Yermakova & Bessonova, 2010).
Simulated defoliation and debudding is one of the ways to evaluate qualitative and quantitative influence of animal damage on tree condition (Hjältén, 2004, Lehtila & Boalt, 2004, Quentin et al., 2010. Such studies on different tree species (Langstrom et al., 1990, 1998, Rozhkov et al., 1991, Chen et al., 2002, Varnagiryte-Kabašinskiene et al., 2015, especially Scots pine (Pinus sylvestris L.) (Lyytikainen-Saarenmaa, 1994, 1999, Wallgren et al., 2014, Nilsson et al., 2016 are very important for Ukraine, where this forest species grows in the 33 % of territory. It was proved (Lyytikainen-Saarenmaa, 1999) that tree reaction on artificial and natural defoliation does not differ, if the needles are removed gradually and in the dates of actual insect feeding. Simulation of buds, branches or roots damage was studied less (Langstrom et al., 1990, Honkanen et al., 1994. Methodological approaches to simulate pine tree damage by insects and to study its effect on tree growth and health condition have been developed and tested in Forest Steppe and Steppe zones in Ukraine (Meshkova et al., 2015). A score for different types of foliage, buds, shoots, branches, stem and root damage was suggested as well as the principles of damage assessment (Meshkova, 2016).
The aim of this research was to evaluate the dependence of Scots pine seedlings mortality and height increment on artificial and large pine weevil caused bud damage.
Objects and methods. Research was carried out in 2013-2017 in two-six-year old Scots pine plantations in the State Enterprise «Zmiyivske Forest Economy».
Over 1000 seedlings were individually marked with soft plate labels in April 2013, considering possible plant damage by unexpected causes, including mechanical damage during weeding or foliage diseases.
For 100 second-year old seedlings were randomly selected for each of two variants with manually removing of buds. In one of them apical buds were manually removed and in other variant apical and lateral buds were manually removed. The dates of such treatment coincided with beginning of large pine weevil maturation feeding and pine shoot growth (Meshkova & Sokolova, 2017).
Such dates were recognized also by needles color change from a yellowish and dull green on a bright green (Meshkova et al., 2015).
The rest labeled seedlings were inspected once a month (end of May, end of June and end of July) in 2013 and once a year (the end of July) in 2014, 2015, 2016 and 2017. Height increment was measured and mortality was registered during such inspection.
Such dates of inspection were chosen considering Scots pine shoot growth timing in the region. It was the most intensive in May and continued up to the end of June. The buds of new generation were formed in July (Meshkova et al., 2015).
At the end of experiment, revision of all records gave the possibility to reject all pines with unplanned damage or disease as well as the plants with buds damage later than in 2013. In result eight groups of 50 pines each with recorded damage history for five years, were selected.
3. Apical and all lateral buds manually removed. 4. Up to 20 % of lateral buds damaged by large pine weevil (low damage). 5. 20-50 % of lateral buds damaged by large pine weevil (moderate damage). 6. Apical bud damaged by large pine weevil (moderate damage). 7. Apical and over 50 to 70 % of lateral buds damaged by large pine weevil (high damage). 8. Apical and over 70 % lateral buds damaged by large pine weevil (high damage).
Plants for variants 4-8 were selected according to the scale (Table 1) (Meshkova, 2016), but groups 7 and 8 were considered as high damage.
Analysis of Scots pine seedlings mortality and height increment in different dates included descriptive statistics. Height increment of Scots pine seedlings in different variants was compared by analysis of variance (ANOVA). Seedlings mortality (percentages) was converted to radians, and the actual value of the Fisher test F was evaluated by formula (1): where φ 1 and φ 2 were the radian values of seedling mortality in compared samples, and n 1 and n 2 were respective sample sizes. The actual value of the Fisher test was compared with the tabulated value for df 1 = 1; df 2 = n 1 + n 2 -2 (Atramentova & Utevskaya, 2008). All statistical analyses were performed using Microsoft Excel applications. Results and discussion. Development of new buds in Scots pine seedlings started at the end of April. In the variants with manually bud removal or large pine weevil damage, new shoots developed since the beginning of May depending on kind of damage. Removal or damage up to 50 % lateral buds did not affect the growth. In the case of removal of apical bud in the central shoot, it was replaced with one of the lateral shoots (Fig. 1). Many accessory buds and bundles of shoots developed in the case of considerable part of buds removing or damaging (Fig. 2). Over 20 new buds were formed in some pines with removal of apical and lateral buds. However, the next year the most of these buds have dried.
Both manually buds removal and large pine weevil damage of Scots pine seedlings in the 3rd decade of April caused their mortality during shoot growth period (in May-July), which considerably exceeded natural mortality of undamaged plants (Fig. 3). Scots pine mortality in all variants trended to increase during the first three months after damage (Fig. 3). Among undamaged plants and plants with up to 20 % of lateral buds damaged mortality did not increase up to the end of June, and was only 6 and 12 % at the end of June and July of the first year of experiment respectively.
Mortality of plants with up to 50 % of lateral buds damaged was 16, 46 and 76 % at the end of May, June and July respectively.
Comparing of plants with manually removed apical buds and with large pine weevil damage of apical buds did not reveal any differences by mortality -20, 56 and 92 % at the end of May, June and July respectively (see Fig. 3).
The plants with apical and lateral buds removed were characterized by the highest mortality (30, 60 and 100 % in May, June and July respectively), but the differences were significant only at the end of July (F fact. =8.2; F 0.05(1; 98) = 4.1).  In the frame of high level of damage significant difference was absent during shoot growth period in the first year of experiment between variants of damage of apical and over 50 % lateral buds and damage of apical apical and over 70 % lateral buds.
Analysis shows, that Scots plant seedlings mortality slowly increased during the next four years, and differences between variants stayed almost the same as in the first season (Fig. 4)  Mortality of the plants with 20 % of lateral buds damaged in 2013 did not differ from that in undamaged plants (see Fig. 4).
In the first year of experiment the growth of apical shoots of Scots pine continued mainly since beginning of May to the end of June. However, it continued also in July in variants, where apical buds were removed at the end of April (Fig. 5).
Height increment of undamaged Scots pine plants was 14.2; 20.1 and 20.6 cm at the end of May, June and July 2013 and did not differ significantly from that in the variants with 20 % or 50 % of lateral buds damaged (in May F fact . = 0.2; F 0.05 = 3.1; in June F fact. = 0.7; F 0.05 = 3.1; in July F fact. = 0.4; F 0.05 =3.1).
Height increment of plants with apical buds removed or damaged was significantly lower (see Fig. 5  In the variants of apical buds manually removal, the height increment in May and June was significantly higher, than in the variant with apical and lateral buds manually removal (in May 1.3 and 0.7 cm respectively; F fact. = 22.9; F 0.05 = 4.0; in June 3.5 and 0.9 cm respectively; F fact. = 8.7; F 0.05 = 4.1). In July any plant did not survive in the variant with apical and lateral buds manually removed.
Comparison of the variants with apical and different proportion of lateral buds damaged show that at the end of May height increment of plants with less proportion of lateral buds damaged was greater. So in May it was 1.2; 1.1 and 0.7 cm in the variants with over 50 %, over 70 % and 100 % buds damaged (F fact. = 6.5; F 0.05 = 3.1), and in June it was 3.1; 2.4 and 0.9 cm in respective variants (F fact. = 20.8; F 0.05 = 3.2).
In July four living plants were found in the variant with apical and over 50 % lateral buds removed.
Annual height increment of undamaged pines increased for 2013-2017 from 20.6 to 41.1 cm (Fig. 6). In 2014 the height increment of plants in the variant with 50 % lateral buds removed in 2013 (29.4 cm) was significantly greater than in undamaged plants (26.7 cm) (F fact. = 3.2; F 0.05 = 3.1). However, the differences between damage of 20 and 50 % of lateral buds were not significant (F fact. = 0.4; F 0.05 = 4.0).
The same feature for height increment in the mentioned variants was revealed for 2015 (F fact. = 11.4; F 0.05 = 3.1). In 2016 height increment in the variant of 20 % of lateral buds removal was significantly less, than in undamaged plants and in plants with 50 % of lateral buds removal (F fact. = 11.9; F 0.05 = 3.1). In 2017 undamaged plants had the greatest height increment (41.1 cm), which was significantly greater than in the variants with 20 and 50 % of lateral buds removal (F fact. = 15.7; F 0.05 = 3.1).
Height increment of plants in the variants with apical buds removed and apical buds damaged by large pine weevil did not differ significantly in 14 (F fact. = 0.08; F 0.05 = 7.7) and in 2015 (F fact. = 0.28; F 0.05 = 18.5).
We can suggest that the features of growth increment in the next years after damage do not depend on the way and intensity of damage but mainly on ecological conditions.
Conclusions. The growth of apical shoots of Scots pine seedlings was registered since the beginning of May to the end of June. In the seedlings with manually bud removal or large pine weevil damage, new shoots developed since the beginning of May. Shoot growth continued also in July in seedlings where all apical buds being removed at the end of April.
Mortality of Scots pine seedlings with 20 % of lateral buds damaged did not differ from that in undamaged plants. The plants with apical and lateral buds manually removed as well as with apical and over 70 % lateral buds damaged by large pine weevil have died in 2013. The plants with apical buds damaged as well as the plants with apical and over 50 % lateral buds damaged have died on the 4 th year after damage.
Removal or damage up to 50 % lateral buds did not affect the growth of Scots pine seedlings. Height increment of plants with apical buds manually removed and damaged by large pine weevil did not differ significantly in May and June of the year of treatment. In July the greater height increment was statistically proved for variant with manually removing of apical bud.
Previously suggested scale of Scots pine seedlings bud damage satisfactory reflects the score of large pine weevil injuriousness.