The behavior of the larch casebearer (<Emphasis Type="Italic">Protocryptis sibiricella</Emphasis>, Lepidoptera,Coleophoridae) in sustained outbreak sites: Communication 2

During a study of the larch casebearer Protocryptis sibiricella (Falkovitsh, 1964) in a forest-steppe larch forest of the Kuznetsk Alatau foothills, the existence of its sustained outbreaks was for the first time shown to depend on the behavior of adults during oviposition. The dispersal distance of the adults was experimentally assessed. The females preferred to lay eggs on the larch needles already damaged by the same species. The attractivity of needles damaged naturally by the pest and artificially was compared.     

The behavior of the larch casebearer (<Emphasis Type="Italic">Protocryptis sibiricella</Emphasis>, Lepidoptera,Coleophoridae) in sustained outbreak sites: Communication 1

The effects of the trophic behavior of the larch casebearer Protocryptis sibiricella (Falkovitsh, 1964) on the existence of sustained outbreak sites were monitored in 1995–1998 in a forest-steppe larch forest of the Kuznetsk Alatau foothills. The trophic behavior of the larch casebearer (partial and multiple damage to needles, coincidence of intense feeding of adult larvae with active regeneration in the larch crown) facilitates stable resistance of trees to secondary pests even at maximum densities of the miner.     

Anomalous outbreaks of an invasive defoliator and native bark beetle facilitated by warm temperatures,changes in precipitation and interspecific interactions

Biotic disturbance agents such as insects can be highly responsive to climatic change and have widespread ecological and economic impacts on forests. Quantifying the responses of introduced and native insects to climate, including how dynamics of one agent may mediate those of another, is important for forecasting disturbance and associated impacts on forest structure and function. We investigated drivers of outbreaks by larch casebearer Coleophora laricella, an invasive defoliator, and eastern larch beetle Dendroctonus simplex, a native, tree‐killing bark beetle, on tamarack Larix laricina from 2000 to in Minnesota, USA. We evaluated the utility of temporal, spatial and climatic variables in predicting the presence/absence of outbreaks of each insect in cells of rasterized aerial survey data. The role of defoliation by larch casebearer in outbreaks of eastern larch beetle was also investigated. For both species, the most important predictors of outbreak occurrence were proximity of conspecific outbreaks in space and time. For larch casebearer, outbreak occurrence was positively associated with spring precipitation and warmer growing seasons. Outbreak occurrence of eastern larch beetle was positively associated with warmer and dryer years and was more likely in cells with prior defoliation by larch casebearer. Our results demonstrate that climate can drive large scale outbreaks of introduced and non‐native disturbance agents on a single host species, and that interactions at the tree level between such agents may scale up to manifest across large temporal and spatial scales.     

Niche‐based relationship between sympatric bark living insect pests and tree vigor decline of Pinus yunnanensis

Forest stands of Pinus yunnanensis Franch in southwestern China are seriously damaged by several bark living insect pests. These pests commonly exist in the same host tree and exploit limited phloem resources. In this study, we hypothesized that sympatric pests would occupy different ecological niches to reduce interspecific competition, and their coordinated attack would aggravate the tree vigor decline of P. yunnanensis. To quantify the ecological niches, we used a sampling method involving three dimensional divisions of tree resource states: (a) sample plot dimension (to evaluate the extent of pest colonization at plot scale), (b) trunk height dimension, and (c) tree vigor dimension. Those attacked pine canopies and colonized trunks were analysed in the field study. The results showed that Tomicus minor and Tomicus yunnanensis both widely and uniformly distributed in lightly, moderately and heavily damaged canopies while they aggregated on particular trunks of dying and withered trees. Lower and middle trunk sections (1–4 m) were mainly occupied by Monochamus alternatus and T. minor, yet T. yunnanensis dominated the upper parts (5–6 m). There was an overlap of the pine shoot beetles in the middle sections (2–4 m), whereas all three species were ecologically segregated in other trunk sections. During the shoot feeding phase, tree vigor declined with pine shoot beetles' increasing shoot feeding density. They coexisted in the same host tree, while M. alternatus only attacked dying and withered tree trunks, causing a greater infestation. Colonization of pine shoot beetle then followed by M. alternatus could be the major causes of tree mortality. This study highlights the resource utilization pattern of sympatric bark living insect pests corresponding with tree vitality. Those findings would help to understand the mechanisms of pest outbreak in P. yunnanensis ecosystem and provide potential guidance for developing an early monitoring pest warning system.     

Growth of regenerated tree seedlings associated with microclimatic change in a mature larch plantation after harvesting

In order to further develop methods of sustainable forest management, we evaluated the effects of logging practices during the winter on microclimatic factors and growth of four seral deciduous broad-leaved tree seedlings regenerated in a larch plantation in northern Japan. We found that winter logging practices drastically changed microclimatic factors, especially in terms of light intensity and the vertical distribution pattern of CO₂ concentration. Harvesting overstory larch trees increased photosynthetic photon flux (PPF), which may enhance the photosynthesis of understory plants. We examined the undergrowth for tree seedlings of the following species: two late successional species, Prunus ssiori and Carpinus cordata; one gap phase species, Magnolia hyporeuca; and one mid-late successional species, Quercus mongolica var. crispula. All of the four studied tree species responded well to the practices of winter logging after the second year of harvesting overstoried larch trees. The current shoot diameter and current shoot length increased significantly. Therefore, we conclude that winter logging practices should improve shoot growth of deciduous broad-leaved tree seedlings regenerated in a larch plantation through the change in environmental factors that accompanies larch harvest.     

Ecological consequences of invasion of <Emphasis Type="Italic">Phyllonorycter issikii</Emphasis> (Lepidoptera,Gracillariidae) in lime forests in Udmurtia

The influence of the lime miner, Phyllonorycter issikii, on the productivity and reproductive parameters of the small-leaved lime Tilia cordata was studied. An increasing infestation of the host plant had a significant negative effect on the linear growth of the shoots and the radial increment of the trunk, the formation of annual rings, the number of inflorescences, and sugar content in the nectar. The latter factor may create a direct threat to the efficiency of local beekeeping. It is recommended that the lime miner be included into the list of domestic quarantine objects of the Russian Federation, and that the population state of this pest be monitored.     

Infestation of the coccid,Icerya seychellarum (Westw.), on the mangrove Avicennia marina (forsk.) vierh. on Aldabra Atoll,with special reference to tree age

Summary The level of infestation by the coccid Icerya seychellarum on the mangrove tree Avicennia marina was measured on a stand of ca. 670 trees on Aldabra Atoll in 1978. Trees varied in basal trunk diameter (btd) between 3 and 30 cm. Leaf infestation increased significantly with increasing btd-class and young trees (btd 3.0–4.5 cm) had a mean infestation of 0.3 mg coccids g^-1 leaf whilst the heaviest infested trees (btd 13.0–14.5 cm) supported 7.6 mg g^-1. Leaf and shoot growth were not correlated with coccid infestation but shoot vigour (leaf to green shoot ratio) declined significantly with increasing btd-class (or age). Leaves of older, heavily infested trees did not differ from those of young uninfested trees in the concentration of soluble or total nitrogen of in four other leaf elements, indicating that nutrient status was not an important factor in infestation. Field observations showed that many of the older trees were subjected to poor drainage which may have increased their susceptibility to attack and also that on the leaves of young trees salt secretion presented an effective barrier to the establishment of coccids. re19800212     

Gypsy moth-induced growth decline of Larix sibirica in a forest-steppe ecotone

Effects of a gypsy moth attack on the productivity of Larix sibirica on tree-ring width were analyzed in a case study of a mountain site in the western Khentey in the northern Mongolian forest-steppe ecotone. A major aim of the study was to assess whether reduced productivity by gypsy moth herbivory could contribute to fluctuations of the forest edge to the steppe in larch-dominated woodlands. In the year of the infestation, larch trees at the forest edge lost 90% of their needles and latewood formation was strongly reduced. However, earlywood formation was widely completed before the gypsy moth attack and, therefore, total tree-ring width was not below the average of the five years prior to infestation. In the two years following the gypsy moth invasion, annual stem increment was strongly reduced. Trees growing 30–100 m inside the forest showed a much weaker response of tree-ring widths to the gypsy moth infestation consistent with significantly higher defoliation at forest edge than in the forest interior. Old trees exhibited a stronger growth decline than middle-aged trees, indicating higher infestation of dominant, exposed trees, which are thought to be better accessible to the wind-dispersed gypsy moth larvae hatching in the early growing season on the steppe. Under the current climate, occasional growth reductions are thought to be of little effect on the performance of L. sibirica, as fast-growing competitors of other tree species, which are not or hardly affected by gypsy moth, are absent.     

Micropropagation ofLarix decidua Mill. andpinus sylvestris L.

Shoot multiplication of Larixdecidua was achieved using axillary and adventitious buds. The formation of axillary buds was stimulated on shoot tips soaked in a cytokinin solution (BAP 10-50 mg 1⁻¹ for 2–4 h. Adventitious buds were induced on cotyledons, needles and vegetative buds cultured on WPM or QL medium supplemented with cytokinin (BAP 1–3 mg 1⁻¹). The shoot formation from induced axillary and adventitious buds was promoted on WPM or QL medium containing a low concentration of auxin (IBA 0.1 mg 1⁻¹). Shoot multiplication of Pinussylvestris was stimulated on WPM, MS, and QL media supplemented with a low concentration of cytokinin (BAP 0.2 mg 1⁻¹) and auxin (IBA 0.1 mg 1⁻¹). Shoot segments produced 2–5 new axillary shoots within 4–5 weeks. Root initiation was stimulated on larch and pine shoots cultured first on WPM supplemented with auxins (NAA and IBA) and later transferred to auxin-free medium.     

Distribution of extractive substances in wood of the Siberian larch (Larix sibirica Ledeb.)

A distribution of extractive substances by height on the trunk and radius of the wood of the Siberian larch (Larix sibirica Ledeb.) was investigated. The maximum flavonoid content in terms of dihydroquercetin (the main flavonoid of the larch wood) was shown to be in the butt part of the tree. In the radial direction, this parameter increased from the center to periphery of the heartwood and reached the maximum value at the sapwood boundary. The maximum content of arabinogalactan (AG) was observed in the bottom and in the top of the trunk. The distribution of the extractive substances was studied in roots of the Siberian larch for the first time.     

THE INFLUENCE OF PHOTOPERIOD AND EXOGENOUS NITROGEN-CONTAINING COMPOUNDS ON THE REPRODUCTIVE CYCLES OF THE LIVERWORT CEPHALOZIA MEDIA

The effects of photoperiod and a number of metabolites (inorganic nitrogenous compounds, amino acids, and growth substances) on reproductive differentiation in the leafy liverwort Cephalozia media Lindb. were studied under axenic conditions. The increase or decrease in the number of branches bearing localized reproductive structures was used to determine the influence of the experimental variables on the regulation of both asexual and sexual phases of reproductivity (production of gemmae and gametangia). Within the context of photoperiodic control, the magnitude of the normal reproductive response was significantly stimulated or inhibited by low concentrations of certain amino acids or kinetin. Certain metabolites (10^-6M concentrations of arginine, cysteine, tryptophan plus kinetin) were able to overcome photoperiodic control of the reproductive response. Generally, organic compounds which stimulated asexual reproductivity under short photoperiod inhibited sexual reproductivity under long photoperiod. Exogenous inorganic nitrogen did not significantly affect the asexual or sexual reproductive response.     

Effect of hydrothermal conditions of permafrost soil on radial growth of larch and pine in Central Yakutia

Results of an investigation of radial growth of Larix cajanderi Mayr and Pinus sylvestris L. in Central Yakutia are presented. The time span of the constructed tree-ring chronologies is more than 200 years. Dendroclimatological analysis revealed a close relationship of tree growth on permafrost soils with climatic factors and soil hydrothermal conditions. A significant correlation of radial growth of larch and pine trees in Central Yakutia with soil temperature and moisture at various depths was found for the first time by statistical analysis.     

NATURAL REGENERATION OF GINKGO BILOBA FROM DOWNWARD GROWING COTYLEDONARY BUDS (BASAL CHICHI)

This study describes the origin and early development of a distinct organ of clonal regeneration in Ginkgo biloba, the basal chichi. These aggregates of suppressed shoot buds originate from superficial meristems located in the cotyledonary axils of all Ginkgo seedlings as part of their normal ontogeny. Within 6 wk of germination these buds become embedded in the cortex of the stem, and their subsequent growth and development occurs below the surface of the bark. When stimulated by some traumatic event that damages the seedling axis, one of these embedded cotyledonary buds usually grows down from the trunk to form a woody, rhizomelike basal chichi which, under appropriate conditions, is capable of generating both aerial shoots and adventitious roots. Vegetative regeneration by means of basal chichi has not only contributed to the long-term persistence of G. biloba in the forests of China, but may also have played a role in the remarkable survival of the genus since the Cretaceous.     

Allopatric populations of the invasive larch casebearer differ in cold tolerance and phenology

1. Traits of non-native insect herbivores may vary spatially due to local genetic differences, rapid post-introduction evolution, and/or novel host plant associations. 2. Populations of larch casebearer, Coleophora laricella Hübner, originally from Europe have likely been isolated for > 60 years in North America on eastern larch, Larix laricina (Du Roi) K. Koch, and western larch, Larix occidentalis Nutt. 3. This study investigated cold tolerance and phenology of larvae collected from eastern larch in Minnesota, and western larch in Oregon, Idaho, and Montana, U.S.A. 4. Mean supercooling points of larvae from Minnesota were up to 10 °C lower than supercooling points of larvae from Oregon, Idaho, and Montana. 5. At ambient environmental conditions in spring, overwintering larvae from Minnesota required a mean (± SE) of 172 ± 19 degree-days above 5 °C to break winter quiescence and actively wander, significantly more than required by larvae from Oregon (66 ± 4), Idaho (64 ± 1), and Montana (60 ± 2). 6. Across all assays and despite substantial latitudinal and elevational variation among western larch sites, no significant differences in any traits were detected among larvae collected from western larch. 7. Spatial variation in cold tolerance and phenological traits of larch casebearer may be attributable to insect genetic differences and/or host plant effects, but exact mechanisms remain unknown. Differences in thermal biology between regions may result in disparate effects of climate change on insect populations and should be accounted for when forecasting insect dynamics across large spatial scales.     

Carbon allocation in shoots of alpine treeline conifers in a CO<Subscript>2</Subscript> enriched environment

With a new approach we assessed the relative contribution of stored and current carbon compounds to new shoot growth in alpine treeline conifers. Within a free air CO₂ enrichment experiment at the alpine treeline in Switzerland, ¹³C-depleted fossil CO₂ was used to trace new carbon in the two tree species Larix decidua L. and Pinus uncinata Ramond over two subsequent years. The deciduous L. decidua was found to supply new shoot growth (structural woody part) by 46% from storage. Surprisingly, the evergreen P. uncinata, assumed to use current-year photosynthates, also utilized a considerable fraction of storage (42%) for new wood growth. In contrast, the needles of P. uncinata were built up almost completely from current-year photosynthates. The isotopic composition of different wood carbon fractions revealed a similar relative allocation of current and stored assimilates to various carbon fractions. Elevated CO₂ influenced the composition of woody tissue in a species-specific way, e.g. the water soluble fraction decreased in pine in 2001 but increased in larch in 2002 compared to ambient CO₂. Heavy defoliation applied as an additional treatment factor in the second year of the experiment decreased the lipophilic fraction in current-year wood in both species compared to undefoliated trees. We conclude that storage may play an important role for new shoot growth in these treeline conifers and that altered carbon availability (elevated CO₂, defoliation) results in significant changes in the relative amount of mobile carbon fractions in woody tissue. In particular, stored carbon seems to be of greater importance in the evergreen P. uncinata than has been previously thought.     

Induction of conifer immune responses by phytopathogenic fungus metabolites

The elicitor activity of compounds extracted from the mycelia of six species of phytopathogenic fungi was assessed from the sizes of necrotic lesions on the external surface of the living trunk phloem of five coniferous species inhabiting Siberia: Siberian larch (Larix sibirica L.), Scotch pine (Pinus sylvestris L.), Siberian spruce (Picea obovata Ledeb.), Siberian fir (Abies sibirica L.), and cedar pine (Pinus sibirica (Rupr.) Mayr.). The compounds for inoculation were extracted from the mycelium of ascomycetes imperfect, and basidium fungi; the living mycelia of these fungi were also used. The fungal extract or mycelium was placed into the hollows 7 mm in diameter in the trunk bark. Infection triggered the formation of hypersensitivity necrotic lesions in the inner bark exceeding in size those appeared after control wounding of four tree species (larch, pine, spruce, and cedar); fir was an exclusion. In experiments with tree trunks and conifer calluses, a dependence of immune response parameters (the sizes of necrotic lesions and the content of lignin and bound proanthocyanidins) on the quantity of the fungal preparation was elucidated. The largest necrotic lesions appeared after injection of 500μg of the fungal preparation into the hollow in the trunk, and its higher quantities did not increase the indices measured. The size of the necrotic lesion on the trunk bark is supposed to be used as a promising index characterizing the level of tree immunity and tolerance under various ecological conditions.     

Influence of mechanical impedance on root exudation of maize seedlings at two development stages

Studies were undertaken to evaluate the effects of mechanical impedance on root exudation by maize (Zea mays L., var Dea) and to examine the importance of these effects in relation to the stage of plant development. Plants were grown under sterile and hydroponic conditions. Mechanical impedance was simulated using glass beads of 1 mm diameter. This treatment was compared with a control without beads. Results demonstrated that plant growth was influenced by mechanical impedance. Mechanical impedance markedly affected the growth of the shoot, whether this was measured as leaf area or total dry matter. Besides increasing root/shoot biomass ratios, mechanical impedances also stimulated root exudation of organic and inorganic compounds. Stressed plants lost more nitrogenous compounds than control plants. Otherwise, the percentage of released carbon decreased. Depending on the developmental stage of the plant, there was a large variation in the magnitude and time course on mechanical impedance effects. The effects of mechanical impedance persist and accentuate with time.     

Aphids at crossroads: when branch architecture alters aphid infestation patterns in the apple tree

Plant architecture highly constrains pest infestation but is rarely considered in studies on plant–insect interactions. We analysed the relationships between apple tree architectural traits manipulated by tree training and within-branch development of Dysaphis plantaginea (rosy apple aphid, RAA), a major apple pest, during its multiplication wingless phase in spring. We hypothesised that the degree of branching had an effect on RAA within-branch infestation. In an experimental apple orchard, the infestation by aphid wingless forms was surveyed in two consecutive spring seasons within branches manipulated to design contrasted architectures differing in shoot numbers, shoot density and branching orders. Whatever the branch management system, aphid infestation was higher on long versus short, fruiting versus vegetative, and growing versus non-growing shoots. Either less infested shoots or less severe infestation were observed in the most branched system. A pattern of within-branch short-distance infestation was confirmed. Moreover, the number of branching points between two shoots exerted a high constraint on this infestation pattern. Beside possible trophic effects due to plant growth patterns already documented in the literature, a high degree of branching is likely to be a key-architectural trait to constrain within-branch aphid infestation. This opens new perspectives on the manipulation of branch architecture as a mean giving partial control of pests towards sustainable fruit production.     

Comparison of insect,fungal, and mechanically induced defoliation of larch: effects on plant productivity and subsequent host susceptibility

Summary Larch sawfly, Pristiphora erichsonii Hartig, and larch needlecast fungus, Mycosphaerella laricinia (R. Hartig) Neg., are early season defoliators restricted only to Larix host trees. Larch defoliation (100%) by either the fungus or insect, but not mechanical removal, induced systemic responses that reduced sawfly consumption and digestion rates one year later. In a feeding behavior assay, larvae quickly abandoned seedlings previously defoliated by M. laricinia. Adult female oviposition choice and egg deposition were unaffected. Seedling growth was not affected during the year of defoliation by M. laricinia, but was significantly reduced one year later. Defoliation by M. laricinia reduced stem volume, radial growth, root biomass and new shoot production. The latter tissue is the only oviposition resource for larch sawfly, and, in contrast, is not influenced by sawfly feeding. We hypothesize that M. laricinia infection may limit larch sawfly populations where both species coexist. However, this reduction is at a substantial net cost to larch productivity.     

Optimization of Factors Influencing Adventitious Rooting in Hybrid Larch

Optimization of in vitro adventitious root induction contributes to the development of a large-scale production system of hybrid clone seedlings of larch (Larix spp.). We used orthogonal testing to investigate the factors that affect the rooting of hybrid larch shoots–activated carbon, vitamin B1, sucrose, glycine, glutamic acid (Glu), cysteine, pH, and induction time in the dark and indole-3-butyric acid (IBA). Variance analysis showed that the effects of sucrose concentration on rooting rate, survival rate, and average root number, pH on the average number of roots; and Glu on survival rate were all significant (p < 0.05) when compared to the mock treatments. Among all of the 45 treatments, the highest rooting rate was 90%, the highest survival rate was 100%, and the highest average root number was 11.8. The theoretically optimal procedure of in vitro root induction of hybrid larch shoots is shoot induction on L9 modified medium (pH 6.7) containing 2 mg.L^–1 naphthalene acetic acid, 0.25 mg.L^–1 IBA, 1/3 macroelements, 7.5 g.L^–1 sucrose, and 5 mg.L^–1 Glu for 8 days, and then root induction on L9 modified medium without auxin.