Extra Food Supply Decreases Damage by the Pine Weevil Hylobius abietis

It has been suggested that reduced damage by the pine weevil ( Hylobius abietis ) under shelter trees might result from more food being available under shelter trees than on clear-cuttings. The shelter trees provide an extra supply of bark on branches and roots. Moreover, shelter trees favour some species in the ground vegetation (e.g. bilberry, Vaccinium myrtillus ) that could be used as food by the weevil. Two similarly designed field experiments, studied whether the amount of pine weevil feeding on planted conifer seedlings was affected by the availability of other food sources. In the first experiment, fresh pine branches were placed weekly on the ground for 6 weeks on a fresh clear-cutting in southern Sweden. This significantly reduced the amount of feeding on seedlings in treated 20 2 20 m plots. In the second experiment, damage tended to increase after mechanical removal of field vegetation (mainly bilberry), but the effect was not statistically significant. In conclusion, extra food in the form of coniferous bark could relieve seedlings from pine weevil damage; however, any effect of this kind due to the presence of field-layer vegetation remains to be demonstrated. Finally, there may be long-term population effects because of the extra food that the shelter trees provide for the reproductive weevils.     

Persistence of deltamethrin against Hylobius abietis on Norway spruce seedlings

Abstract

The pine weevil Hylobius abietis L. is major threat to forest regeneration in the Nordic countries. The persistence of the deltamethrin insecticide used against pine weevil on Norway spruce seedlings was studied after the seedlings were dipped or sprayed. Insecticide application was timed to occur either before or after frozen storage. Bioassays with the stems of Norway spruce seedlings were used to determine the effect of the insecticide against feeding by the pine weevil. The measures of the control effect were reduction in area of gnawed bark and the state of health of the pine weevils. The concentration of deltamethrin decreased rapidly in seedlings, especially after spraying treatment, which did not efficiently protect seedlings against the pine weevil 6 weeks after planting. There were no signs of degradation of deltamethrin or of an effect on seedling height after frozen storage. In bioassay, the amount of deltamethrin that efficiently prevented feeding by the pine weevil was 5.5 µg g^?1 fresh weight. After one growing season in the field, about 1.76–2.24 µg g^?1 (13–15% of the initial level) of dipped deltamethrin remained in the seedlings. In seedlings treated by spraying, 0.93–0.98 µg g^?1 (7–8% of the initial level) of the deltamethrin remained. According to bioassays, these amounts were no longer sufficient to protect seedlings from feeding by the pine weevil. Therefore, in the first summer, dipping was a significantly more efficient method of application for control of pine weevils.     

Replanting conifer seedlings after pine weevil emigration in spring decreases feeding damage and seedling mortality

Replanting at appropriate times after harvesting a coniferous forest stand can help efforts to suppress seedling mortality caused by the pine weevil Hylobius abietis, but optimal times are uncertain. We hypothesized that planting in June rather than May in the third season after harvest would reduce feeding damage by the pine weevil and increase seedling survival rates in central Sweden, where new-generation weevils mainly fly away from their development sites in May/early June. An experimental test of the hypothesis in eight clear-cuts confirmed that planting in June instead of May reduced proportions of seedlings attacked by pine weevil, bark removal from seedlings’ stems, and proportions of seedlings killed by feeding damage. These differences between seedlings planted in May and June declined to some extent with time but still remained significant after two growing seasons. The total seedling mortality after two seasons did, however, not differ significantly between seedlings planted in May and June. Overall, 29% of all seedlings were killed by pine weevil, 4.0% by Hylastes bark beetles, and 2.3% by drought. The results indicate that replanting in spring during the third season after harvest can advantageously continue until mid-June with respect to damage and mortality.     

Role of monoterpenes in Hylobius abietis damage levels between cuttings and seedlings of Picea sitchensis

Abstract

This study investigated the role of monoterpenes, a group of chemicals known to be involved in plant defence, in the susceptibility of Sitka spruce [Picea sitchensis (Bong.) Carr.] plants derived from both cuttings and seedlings to attack by the large pine weevil Hylobius abietis (L.). Results showed that, given the choice, weevils prefer to feed on the shoots of seedlings than of cuttings and that this preference continued over a period of 6 days, although the overall level of feeding declined. This observation was associated with a higher level of monoterpenes in the shoots from cuttings than in those from seedlings. When the weevils were restricted to the stems and given no choice, levels of damage to the bark were similar in both plant types.     

Influence of Stem Diameter on the Survival and Growth of Containerized Norway Spruce Seedlings Attacked by Pine Weevils (Hylobius spp.)

Pine weevils (Hylobius spp.) feeding on stem bark of young conifer seedlings pose a serious threat to forest regeneration-planting programmes in Nordic countries. This study was designed to determine the threshold diameter for planted, untreated containerized seedlings, above which pine weevils cause little or no damage. The effects of sublethal weevil damage on seedling growth were also assessed. In total, 5320 containerized spruce seedlings were planted on scarified and unscarified plots on three sites in southern Sweden. Seedlings in six size classes, which differed with regard to age (1.5-3.5 yrs) and cultivation density (28-446 seedlings m 2) were grown using the Combicell system. None of the seedlings was treated with insecticides, except for those in the smallest class, where both untreated and treated seedlings were used. Inspections were made periodically during the first 3 yrs and after both 5 and 7 yrs. A statistically significant relationship was found between seedling losses due to pine weevil attack and seedling stem-base diameter at the time of planting out, on both scarified and unscarified plots. For seedlings with a stem-base diameter of around 10 mm, mortality due to pine weevil attack on scarified plots was low enough to be considered negligible. This threshold diameter was several millimetres greater for seedlings planted on unscarified plots. An analysis of the relationship between the extent of weevil damage and seedling growth rate showed that among surviving seedlings, those that grew fast tended to show low levels of damage. On unscarified plots, the mortality rate amongst seedlings treated once with a permethrin insecticide was only one-third that of untreated seedlings. On scarified plots, the corresponding difference was somewhat smaller. Repeated insecticide treatment resulted in a pronounced reduction in seedling mortality on the unscarified plots, whereas the effect was weaker on scarified plots.     

Damage by pine weevil Hylobius abietis to conifer seedlings after shelterwood removal

Abstract

Pine weevil (Hylobius abietis L.) damage to seedlings after overstorey removal was investigated in a survey study in six shelterwoods in the south–central part of Sweden. The shelterwoods predominantly consisted of Scots pine, except at one site where the shelter trees mainly consisted of Norway spruce. Before final cutting, 10 plots were laid out at each site and measurements of shelter trees and marked seedlings were taken. The seedlings were examined during the 2 years after final cutting. The study showed that removal of shelter trees increases the risk of severe damage by pine weevil and the variable that was most strongly correlated with the risk was the seedling root collar diameter. Both Scots pine and Norway spruce seedlings were severely damaged by pine weevil, and most of the feeding occurred during the first year after cutting. The amount of debarked area was significantly larger for Scots pine than for Norway spruce seedlings. Vitality (growth of the leading shoot before final cutting) of the seedlings also affected the probability of damage. Seedlings with high vitality were less damaged by pine weevil than seedlings with low vitality. For Scots pine the shelterwood density before final cutting was correlated to the intensity of pine weevil feeding after cutting. In conclusion, after the final cutting of a pine or spruce shelterwood, pine weevils will probably invade the area. To avoid serious damage, Norway spruce and Scots pine seedlings should have reached a diameter of at least 10–12 mm.     

Host Preference by Monochamus alternatus (Hope) during Maturation Feeding on Pine Species and Masson Pine Provenances

Host preferences pine of the sawyer beetle, Monochamus alternates (Hope), during maturation feeding on 8 conifer trees and 40 masson pine provenances, were investigated using 3 types of laboratory bioassay of consistent feeding preference, feeding area and visitation frequency. M. alternatus adults have the highest frequency of feeding and prefer to feed on the branches of P. massoniana and P. densiflora and had significant host selectivity on 8 conifer trees in the area of Nanjing. The adult feeding visitation frequencies were 1 ~3 adults per branch. Maturation feeding areas were much larger on P. massoniana and P. densiflora than on P. taeda, P. elliottii, Juniperus virginiana and Cunninghamia sinensis. After initial selection tests, 12 provenances of masson pine had smaller maturation feeding areas. The second and third selection results showed that 12 provenances and six provenances also had consistent reductions in feeding by M. alternatus. The three provenances Fujian 2, Guangdong 5 and Guangdong     

Risk of Snow Damage in Unmanaged and Managed Stands of Scots Pine,Norway Spruce and Birch

The aim of this study was to assess the risk of snow damage to trees in unmanaged and managed stands of Scots pine (Pinus sylvestris L.), Norway spruce [Picea abies (L.) Karst.] and birch (Betula spp.) over a rotation. The risk assessment was based on the prediction of critical snow loads in interaction with the windspeed at which trees can be expected to break or be uprooted, and on the frequency of long-term extremes of precipitation and of suitable temperature conditions for the accumulation of snow on the tree crowns. The Scots pine stands were found to be more susceptible to snow damage than the others, and an unmanaged stand of Scots pine to be more susceptible to break and uproot than a managed one. Correspondingly, an unmanaged stand of Norway spruce was more susceptible to stem breakage than a managed one, but less susceptible to uprooting. Neither unmanaged nor managed birch stands were likely to suffer any kind of snow damage. The susceptibility of unmanaged stands is caused by low tapering of the trees. Based on the frequency of long-term extremes in precipitation at the temperatures needed for snow accumulation on tree crowns, critical snow loads of 10-19, 20-29 and 30-39 kg m^-2 occurred 19.3, 3.3 and 1.3 times in a decade in southern Finland. Critical snow loads of 10-19, 20-29, 30-39 and 60-69 kg m^-2 occurred in northern Finland 17.0, 6.3, 1.7 and 0.3 times in a decade.     

Pine Weevil Population Density and Damage to Coniferous Seedlings in a Regeneration Area With and Without Shelterwood

Damage to planted conifer seedlings by the pine weevil, Hylobius abietis (L.), is considered to be less severe in shelterwoods than in clear-cuttings. To evaluate possible reasons for this reduction, this study investigated the relationship between seedling damage and pine weevil population density in the presence and absence of shelter trees. Assessments of seedling damage throughout a full growth season and absolute population density estimates were made at a fresh clear-cutting and an adjacent shelterwood (1 ha each). A grid of 100 pitfall traps was placed over each area, and population estimates were made using the mark–recapture technique. Pine weevil damage to seedlings was about twice as high in the clear-cutting, whereas pine weevil density was estimated to be higher in the shelterwood or about the same in the two treatments (～14?000 weevils ha^?1). Existing differences in microclimate between the shelterwood and clear-cutting did not seem to be the cause of the differences in damage levels. Thus, the hypothesis that seedling damage is reduced in shelterwoods because of increased availability of alternative food remains a candidate for further testing.     

Effect of Reforestation Methods on Pine Weevil (Hylobius abietis) Damage and Seedling Survival

Örlander, G.1 and Nilsson, U. (Swedish University of Agricultural Sciences, The Southern Swedish Forest Research Centre, Asa Forest Research Station, S-360 30 Lammhult, Sweden and Swedish University of Agricultural Sciences, The Southern Swedish Forest Research Centre, Box 49, S-230 53 Alnarp, Sweden). Effect of reforestation methods on pine weevil (Hylobius abietis) damage and seedling survival. Received Feb. 16, 1998. Accepted Sept. 15, 1998. Scand. J. For. Res. 00: 000-000, 199X. Damage to Norway spruce (Picea abies (L.) Karst.) seedlings by the large pine weevil, Hylobius abietis (L.) (Coleoptera: Curculionidae), was monitored in relation to clear - cutting age and silvicultural treatments in southern Sweden. New clear - cuttings were established on four sites during five consecutive years, and seedlings were planted on them from 1989 through 1993. In total, 31 774 seedlings were planted on 20 clear - cuttings. The measures evaluated were seedling insecticide treatment, application of herbicide to ground vegetation, scarification (mound) and planting late in the season. In addition, the effects of slash removal and seedling type were studied. The pine weevil was, by far, the dominant damaging agent. Planting without insecticide or soil treatment on fresh, one- or two - year - old clear - cuttings resulted in a mean level of weevil - caused mortality exceeding 60%. The results indicate that the risk of serious damage by pine weevils remains high until the clear - cuttings reach four or five years of age. Killing the vegetation with herbicide had no effect on pine weevil damage. Slash removal decreased damage on older clear - cuttings, but the effect was small. Scarification (mounding) strongly reduced damage. On fresh clear - cuttings the mean mortality caused by pine weevils in mounded plots was 13%, whereas it was 77% in the controls. The mounding effect varied between sites and clear - cuttings of different ages. Late planting (10 June instead of 1 May) reduced damage on two- and three - year - old clear - cuttings. Three - year - old, bare - rooted seedlings were not damaged as seriously as two - year - old, containerized ones, but the effect was probably due to the larger size of the bare - rooted seedlings. Non - lethal injury resulted in reduced seedling growth. Damage by pine weevils varied between years and within growing seasons. However, on fresh, one- and two - year - old clear - cuttings, damage was severe enough to cause high mortality during all studied years.     

Defoliation by the Needle-shortening Pine Gall Midge,Thecodiplosis brachyntera,on Pines in Central Sweden

An outbreak of the needle-shortening pine gall midge, Thecodiplosis brachyntera , occurred on Scots pine, Pinus sylvestris (L.) and lodgepole pine, P. contorta (Dougl.) in central Sweden during 1995-1998. The larval feeding of T. brachyntera kills current-year needles and heavy infestation causes severe defoliation. A pattern of fluctuating defoliation among years and sites was found on both pine species. Defoliation was evenly distributed in the crown of P. sylvestris during years of high as well as low infestation; apical whorls had as much defoliation as basal whorls. In P. contorta , however, there was a tendency for defoliation to be concentrated on branches in the most apical whorls. Growth ring increments on P. sylvestris with high levels of defoliation (71%) did not differ from trees with moderate levels (26%) of defoliation. Shoot lengths were significantly shorter, however, on heavily infested trees the year after defoliation.     

Pine weevil (Hylobius abietis) damage to cuttings and seedlings of Norway spruce

Damage caused by pine weevil (Hylobius abietus L.) to planted seedlings and cuttings of Norway spruce (Picea abies (L.) Karst.) was studied at five clearcut sites in south-eastern Sweden. The main objective was to compare the two types of stock in terms of attack frequency and mortality due to pine weevil feeding. Cuttings and seedlings with the same initial stem-base diameter (4 mm) were compared. Two sites were harvested and scarified shortly before planting, two were harvested shortly before planting, but were not scarified, and one was harvested 2 years before and scarified the autumn before planting. The total mortality 5 years after planting was highest, greater than 90%, at the new, non-scarified sites, and lowest, 23%, at the old, scarified site. More than 90% of the mortality was caused by pine weevil feeding. Attack frequency and pine weevil induced mortality were significantly higher among seedlings than among cuttings. Mortality due to pine weevil damage was 4–43% higher in seedlings than in cuttings after the fifth year. Of the cuttings and seedlings that were attacked in the first year, a significantly higher frequency of the seedlings were girdled. The higher resistance of cuttings to pine weevil damage may partly explain the more rapid growth of cuttings reported in other studies. However, the causes of their higher resistance need to be further investigated. The thicker bark and needles on the stem base of the cuttings could be important in this respect.     

The soil seed bank of the threatened plant <Emphasis Type="Italic">Magnolia stellata</Emphasis> is subordinate to the emergence of current-year seedlings

We studied seed bank formation of the threatened star magnolia, Magnolia stellata, to examine the early stage of regeneration. Forty-five seedling plots (2 × 2 m), each including a soil-sampling quadrat (40 × 40 cm), were established randomly under or around the crowns of mature M. stellata trees. Seeds of M. stellata were collected from each quadrat to a depth of 5 cm. Only four seeds of M. stellata were found (0.56 seeds/m²) and all were located under mature crowns. Current-year seedlings were abundant in water channels, on moss, or under mature crowns, suggesting that the seeds may require wet soil conditions for germination. Magnolia stellata seeds show considerable germination below the crowns of mature trees in the year following masting, while some seeds remain dormant in the soil. Considering the soil seed bank and the current-year seedling bank of M. stellata, a frequent supply of seed is essential for the regeneration of this species. Thus, it is important to maintain mature trees in addition to promoting seed production.     

油松毛虫产卵、取食偏嗜行为及油松针叶内含物测定

[目的]为明确油松毛虫在油松上的产卵和取食部位以及可能机理,为未来害虫发生预测模拟提供基础信息数据。[方法]通过室内模拟试验,统计油松毛虫在盆栽油松幼苗不同部位上的产卵量和取食不同油松针叶的偏嗜情况及死亡率;测定油松针叶内含物含量并与油松毛虫偏嗜行为进行了相关性分析。[结果]在一年生油松针叶上平均产卵块数最多(3.10±0.28),显著高于二年生针叶和三年生针叶;取食一年生油松针叶的油松毛虫数量最多(13.40±0.91)、死亡率最低(13.60%±4.87%),显著优于取食二年生油松针叶和三年生油松针叶的幼虫。油松毛虫幼虫取食选择、成虫产卵选择和幼虫体长与油松针叶内含水量成显著正相关(P0.01);与寄主总酚含量(P0.01)和碳氮比(P0.05)成显著负相关。[结论]油松毛虫对一年生油松针叶具有明显的产卵和取食偏嗜行为。一年生油松针叶内含水量最高、总酚含量最低、有机碳含量最低可能是造成寄主偏嗜行为的原因。     

Higher resistance of the offspring of Scots pine trees resulting from natural regeneration in old foci of Heterobasidion annosum root rot

Abstract

Heterobasidion annosum (Fr.) Bref. is a fungal pathogen causing annosum root rot – one of the most economically important diseases in coniferous stands. The major aim of this study was to compare the resistance of the offspring of Scots pine trees (Pinus sylvestris L.) from seed orchards and the offspring of trees that were naturally reproduced in old foci of the disease. In experiments conducted in vitro, we used 960 seedlings which were grown from seeds collected from 60 trees in 6 old foci of the disease and 640 seedlings grown from seeds collected in 4 seed orchards. The offspring of trees from seed orchards after inoculation with H. annosum had nearly twofold higher mortality rate than the seedlings developed from the seeds collected in old foci of the disease. This suggests that the offspring of self-sown trees in old foci of the disease has a greater, genetically conditioned resistance to annosum root rot.     

Stand Structure in Pine,Spruce and Deciduous Forests: A Comparison Between Finnish and Russian Karelia

This study investigated the stand structure in pine, spruce and deciduous forests in the border district of Finland and Russia. A total of 46 mature forest stands was selected as pairs, the members of each pair being as similar as possible with respect to their forest site type, age, moisture and topography. The stands were then compared between the two countries by means of basal areas and number of stems. The proportions of dominating tree species were 2-12% lower, and correspondingly the proportions of secondary tree species higher, in Russian forests. The density of the forest stock was also higher in each forest type in Russia. The forests in the two countries differed most radically in terms of the abundance of dead trees. The amount was two to four times higher in Russian deciduous and spruce forests, and in pine forests the difference was 10-fold. The stand structures indicated that Russian coniferous stands, in particular, were more heterogeneous than intensively managed pine and spruce stands in Finland.     

Leaf conductance of primary and mature leaves ofPinus roxburghii: A comparison

We used a null-balance porometer to measure leaf conductance of mature and primary leaves of natural seedlings, saplings, and trees ofPinus roxburghii (chir) during autumn at four sites at 1,320–1,930 m elevation in the central Himalaya of India. Our hypothesis that primary leaves had higher leaf conductance than mature leaves (needles in fascicles), based on measurements in other pines, was rejected. Comparisons on the same saplings and seedlings showed lower leaf conductance for primary leaves than for mature leaves. Primary leaves on seedlings and saplings also did not consistently have higher leaf conductance than mature leaves on near-by trees. Mature leaves on seedlings, however, did often have higher conductance than mature leaves on nearby trees. Mean values for leaf conductance (mmol m⁻² s⁻¹, based on total leaf surface area) ranged from 42–82 for mature leaves on trees, 60–121 for mature leaves on seedlings, and 28–67 for primary leaves on seedlings. Compared to published values for other pine species, conductance of mature leaves ofP. roxburghii is relatively low. Funding for this study was provided by grants from the United States National Science Foundation, INT-9312052 and INT-9404043. We appreciate the review of an early draft by Barbara Bond.     

Harvesting of logging residues affects diameter growth and pine weevil attacks on Norway spruce seedlings

Removal of logging residues causes significant nutrient losses from the harvesting site. Furthermore, collection of residues into piles could lead to small-scale differences in establishment conditions for seedlings. We studied the effects of stem-only (SOH) and aboveground whole-tree harvesting (WTH) on Norway spruce (Picea abies) seedling growth and pine weevil (Hylobius abietis) damage at two sites (SE and W Norway). We also compared two planting environments within the WTH plots (WTH-0: areas with no residues, WTH-1: areas where residue piles had been placed and removed before planting). In practice, one-third of the residues were left on site after WTH. After three growing seasons there were no differences for height or diameter increment between SOH and WTH (WTH-1 and WTH-0 combined) treatments. However, relative diameter increment was largest for WTH-1 seedlings and lowest for WTH-0 seedlings. Few seedlings sustained pine weevil attacks at the W Norway site, with no differences among treatments. At the SE Norway site, the percent of seedlings damaged by pine weevils and average debarked area were significantly higher after WTH (82% and 3.3?cm²) compared to SOH (62% and 1.7?cm²). We conclude that WTH may lead to spatial differences in establishment conditions.     

Effects of silicon-rich soil amendments on growth,mortality and bark feeding damage of Sitka spruce (Picea sitchensis) seedlings under field conditions

Alternative methods of protection are required against feeding by the large pine weevil (Hylobius abietis) on the bark of conifer seedlings. Silicon (Si) has been shown to enhance the resistance of plants to insect herbivores. This study investigated the effects of low doses of Si-rich soil amendments on growth, mortality and bark feeding damage of Sitka spruce (Picea sitchensis) seedlings. Two-year old seedlings were grown, individually, in soil taken from a tree nursery treated with coal ash, peat ash, rice husk ash, slag, sodium metasilicate or a commercially available Si fertiliser (Pro-Tekt) and planted out on two reforestation sites in Ireland. Seedlings grew well (about 20% growth in terms of height, 66% in root collar diameter, after two growing seasons), and Si-rich amendments did not have a significant effect on growth or mortality. Bark feeding damage on Si-treated seedlings did not vary significantly from control seedlings. Bark Si concentrations were not significantly larger in treated seedlings than in control seedlings, but control seedlings already had comparatively high bark Si concentrations (560?mg?kg^?1 dry tissue). In conclusion, Sitka spruce seedlings grown in the presence of Si-rich soil amendments prior to planting did not show greater resistance to weevil feeding under the present conditions.     

云南切梢小蠹与横坑切梢小蠹蛀梢期的竞争研究

2000年5月至2001年5月,研究了云南切梢小蠹与横坑切梢小蠹蛀梢期的种间竞争,比较了2种松小蠹在其寄主云南松树冠的垂直分布规律.结果表明,不同月份2种松小蠹在云南松树冠的垂直分布的存在差异,并随着月份的变动而发生变化.横坑切梢小蠹多危害较细的松梢,而云南切梢小蠹多危害较粗大的松梢.2种松小蠹的其它蛀梢习性(危害梢的年龄、攻击部位、蛀道长度等)文中也进行了比较.结论,云南切梢小蠹对云南松树梢的攻击能力强于横坑切梢小蠹.