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.     

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.     

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.     

The Effect of Larch Casebearer on Larch Growth and Reproductive Organ Formation

Dependencies of larch (Larix sibirica Ledeb.) growth and reproductive organ formation on its infestation by a phyllophagous miner, larch casebearer (Coleophora sibiricella Flkv., Lepidoptera, Coleophoridae) were studied. The work was performed in the sustained outbreak of the larch casebearer in the forest-steppe-larch forest at Kuznetsk Alatau. For the representative tree groups, we determined shoot linear growth, the number of axillary buds, trunk radial growth, the number of micro- and macrostrobili produced, and the contents of water, monoses, starch, and nitrogenous compounds in needles as dependent on the infestation density. We found that infestation exceeding 0.5 larvae per brachyblast significantly suppressed tree growth and reproductive organ formation. At this threshold value of infestation, a significant inhibition of shoot linear growth can serve a marker for suppressed trunk radial growth and reproductive organ formation. The lower degree of infestation did not suppress larch growth and even stimulated it. This observation, along with our data on the changes in the composition of nitrogenous and carbohydrate compounds in damaged needles, demonstrates the active character of interaction between the host tree and the phyllophagous insect, a transit of the source function from damaged needles to healthy ones, and the stimulated reparation of the assimilation apparatus.     

Cold tolerance of the invasive larch casebearer and implications for invasion success

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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.     

A novel insight into the regulation of light-independent chlorophyll biosynthesis in <Emphasis Type="Italic">Larix decidua</Emphasis> and <Emphasis Type="Italic">Picea abies</Emphasis> seedlings

Light-independent chlorophyll (Chl) biosynthesis is a prerequisite for the assembly of photosynthetic pigment–protein complexes in the dark. Dark-grown Larix decidua Mill. seedlings synthesize Chl only in the early developmental stages and their Chl level rapidly declines during the subsequent development. Our analysis of the key regulatory steps in Chl biosynthesis revealed that etiolation of initially green dark-grown larch cotyledons is connected with decreasing content of glutamyl-tRNA reductase and reduced 5-aminolevulinic acid synthesizing capacity. The level of the Chl precursor protochlorophyllide also declined in the developing larch cotyledons. Although the genes chlL, chlN and chlB encoding subunits of the light-independent protochlorophyllide oxidoreductase were constitutively expressed in the larch seedlings, the accumulation of the ChlB subunit was developmentally regulated and ChlB content decreased in the fully developed cotyledons. The efficiency of chlB RNA-editing was also reduced in the mature dark-grown larch seedlings. In contrast to larch, dark-grown seedlings of Picea abies (L.) Karst. accumulate Chl throughout their whole development and show a different control of ChlB expression. Analysis of the plastid ultrastructure, photosynthetic proteins by Western blotting and photosynthetic parameters by gas exchange and Chl fluorescence measurements provide additional experimental proofs for differences between dark and light Chl biosynthesis in spruce and larch seedlings.     

Trophic ecology of two savanna grazers,blue wildebeest <Emphasis Type="Italic">Connochaetes taurinus</Emphasis> and black wildebeest <Emphasis Type="Italic">Connochaetes gnou</Emphasis>

The feeding niches and trophic ecology of two South African grazers, blue wildebeest Connochaetes taurinus and black wildebeest Connochaetes gnou, are compared using stable carbon and nitrogen isotope data from feces and tooth dentine collagen. As sympatric, closely related taxa predicted to occupy similar trophic positions, the blue and black wildebeest provide a good model for studying the mechanisms of coexistence and macroevolution in mammals. Data from feces collected from a single reserve in the Free State Province reveal different trophic behaviors between two herds of blue wildebeest and between both compared with a single herd of black wildebeest. These data suggest that sympatric coexistence of blue and black wildebeest is facilitated by differential niche occupation at family group or herd levels, rather than between species. However, such separation does not occur over longer time scales: results from dentine collagen support the hypothesis that the two species are indistinct in terms of trophic behavior, although blue wildebeest show more feeding flexibility, probably because of their wider habitat tolerance range. Similarities in premaxillary width of males and females of both species also suggest that both species are adapted to similar feeding styles. Thus, it is unlikely that changes in trophic behavior provided the trigger for divergence of the black from the blue wildebeest lineage in the Middle Pleistocene. We argue that the case of these two species represents an example of speciation that was not driven by resource competition, as is often assumed for many turnover events in mammalian evolution. We briefly discuss a previous suggestion that links black wildebeest evolution to their more territorial breeding behavior associated with Middle-to-Late Pleistocene landscape changes in southern Africa.     

The effect of food concentration and population density of mosquito larvae (<Emphasis Type="Italic">Anopheles stephensi</Emphasis>, Diptera,Culicidae) on their feeding behavior

The influence of food concentration and population density on the feeding behavior of Anopheles stephensi (Diptera, Culicidae) larvae has been shown experimentally. Lack of food resulted in larvae switching from sweeping the surface film to scraping the substrate off the bottom. The effect of the larval population density was more complex and depended on the food concentration. As a result, the ratio between the larvae keeping to the surface and to the bottom of the vessel was determined by interactions which led to their redistribution between the two trophic niches: the surface film and the bottom substrate. The traits observed ensure plasticity in the use of trophic resources within a water body.     

Population structure of the pecan nut casebearer Acrobasis nuxvorella throughout its geographical distribution

• 1 The pecan nut casebearer Acrobasis nuxvorella Neunzig (Lepidoptera: Pyralidae) is an important, monophagous pest of pecan Carya illinoinensis (Fagales: Juglandaceae).
• 2 This pest is native from Louisiana west to the eastern edge of New Mexico and north to Illinois in the U.S.A. and as far west as Chihuahua and south to Oaxaca in Mexico.
• 3 Recently, this pest has expanded beyond the native range of pecan into regions where pecan has been introduced for cultivation.
• 4 Amplified fragment length polymorphism markers were used to determine the population genetic structure of this insect pest across its current geographical distribution.
• 5 Population genetic analyses indicate a great degree of genetic structure in the pecan nut casebearer across its geographical distribution, with genetically distinct populations occurring in those areas where the pecan nut casebearer is not native but has been invasive.

     

The effects of foliage damage on casebearing moth larvae, Coleophora serratella, feeding on birch

ABSTRACT.

• 1 Mechanical damage to birch (Betula pendula Roth) leaves leads to an increase in the concentration of phenolic compounds, which spreads throughout the leaf within 8 days.
• 2 Coleophora serratella L. (Lepidoptera: Coleophoridae) apparently responds to this chemical change over a similar time scale. Within 24 h of pin-pricking leaves the casebearer moves from the immediate vicinity of the damage, but is just as likely to move to an undamaged portion of the damaged leaf as to vacate the leaf entirely. After 8 days mines on undamaged portions of damaged leaves were significantly smaller than mines on undamaged leaves.
• 3 Furthermore, Coleophora serratella reared on damaged trees took an average of 3 days longer to develop than those reared on undamaged trees.
• 4 It has been suggested that increased movement in response to damage-induced chemical changes causes hyperdispersed damage on plant foliage. Both within and between-leaf casebearer damage patterns were shown to be aggregated on birch.
• 5 Thus although mechanical damage can induce chemical and behavioural changes in the field, these are not reflected in the observed damaged patterns. We speculate on several possible reasons for this.

     

Development of a sequence characterized amplified region (SCAR) marker associated with high rooting ability in <Emphasis Type="Italic">Larix</Emphasis>

In this study, bulked segregant analysis (BSA) was used on Larix leptolepis × Larix olgensis hybrids to identify a random amplified polymorphic DNA (RAPD) marker associated with high rooting ability in larch. Two DNA bulks: H (high rooting ability) bulk and L (low rooting ability) bulk were constructed according to the rooting percentages of the stock plants. Among the 328 primers, only S356 could amplify a specific band, named S356₄₄₅, which only existed in the H bulk and was further confirmed following selective genotyping of individual hybrids. Grounded on the border sequences, S356₄₄₅ was converted to a sequence characterized amplified region (SCAR) marker, HRL445, which can be useful in marker-assisted selection (MAS) to screen for larch with high rooting ability. All the results strongly indicated that S356₄₄₅ and HRL445 were closely associated with high rooting ability in larch.     

Application of AFLP, RAPD and ISSR markers to genetic mapping of European and Japanese larch

Genetic linkage maps have been increasingly developed for a wide variety of plants, using segregating populations such as F₂s or backcrosses between inbred lines. These pedigrees are rarely available in outbred species like forest trees which have long generation times. Thus genetic mapping studies have to use peculiar pedigrees and markers in appropriate configurations. We constructed single-tree genetic linkage maps of European larch (Larix decidua Mill.) and Japanese larch [Larix kaempferi (Lamb.) Carr.] using segregation data from 112 progeny individuals of an hybrid family. A total of 266 markers (114 AFLP, 149 RAPD and 3 ISSR loci) showing a testcross configuration, i.e.heterozygous in one parent and null in the other parent, were grouped at LOD 4.0, θ=0.3. The maternal parent map (L. decidua)consisted of 117 markers partitioned within 17 linkage groups (1152 cM) and the paternal parent map (L. kaempferi) had 125 markers assembled into 21 linkage groups (1206 cM). The map distance covered by markers was determined by adding a 34.7-cM independence distance at the end of each group and unlinked marker. It reached 2537 cM and 2997 cM respectively for European larch and Japanese larch, and represented respectively a 79.6% and 80.8% coverage of the overall genome. A few 3:1 segregating markers were used to identify homologous linkage groups between the European larch and the Japanese larch genetic maps. The PCR-based molecular markers allowed the construction of genetic maps, thus ensuring a good coverage of the larch genome for further QTL detection and mapping studies. Received: 15 March 1999 / Accepted: 29 March 1999     

Plasticity in gas‐exchange physiology of mature Scots pine and European larch drive short‐ and long‐term adjustments to changes in water availability

Adjustment mechanisms of trees to changes in soil‐water availability over long periods are poorly understood, but crucial to improve estimates of forest development in a changing climate. We compared mature trees of Scots pine (Pinus sylvestris) and European larch (Larix decidua) growing along water‐permeable channels (irrigated) and under natural conditions (control) at three sites in inner‐Alpine dry valleys. At two sites, the irrigation had been stopped in the 1980s. We combined measurements of basal area increment (BAI), tree height and gas‐exchange physiology (Δ¹³C) for the period 1970–2009. At one site, the Δ¹³C of irrigated pine trees was higher than that of the control in all years, while at the other sites, it differed in pine and larch only in years with dry climatic conditions. During the first decade after the sudden change in water availability, the BAI and Δ¹³C of originally irrigated pine and larch trees decreased instantly, but subsequently reached higher levels than those of the control by 2009 (15 years afterwards). We found a high plasticity in the gas‐exchange physiology of pine and larch and site‐specific responses to changes in water availability. Our study highlights the ability of trees to adjust to new conditions, thus showing high resilience.     

Invasive Predator, <Emphasis Type="Italic">Bythotrephes</Emphasis>, has Varied Effects on Ecosystem Function in Freshwater Lakes

Bythotrephes longimanus is an invertebrate predator that has invaded the North American Great Lakes and a number of inland lakes, where it preys on crustacean zooplankton. We examined the effect of Bythotrephes on two measures of ecosystem function during a four-month observational study of freshwater lakes on the boreal shield. Bythotrephes-invaded lakes had significantly lower epilimnetic zooplankton abundance and production compared to reference lakes. On average, Bythotrephes consumed 34% of zooplankton production when it was present in lakes. There was some evidence of changes in the timing of zooplankton production, as well as shifts to cooler, less productive habitats, which may lessen the overall effect of the invader on the transfer of energy to higher trophic levels. We experimentally demonstrated a weak trophic cascade where invader predation reduced zooplankton biomass, and subsequently increased phytoplankton growth. However, the response was small in magnitude and not biologically relevant at the whole lake-scale. The most conspicuous effect of Bythotrephes that we measured was a diversion of energy away from native predators at higher trophic levels. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Colour of larch heartwood and relationships to extractives and brown-rot decay resistance

Larch heartwood is appreciated for its good mechanical properties, its colour and its texture, and it is often used outdoors because of its natural durability (decay resistance). In this study the colour of larch heartwood was studied in relation to extractives and decay resistance, with the aim to estimate durability of larch heartwood from its colour. On a total of 293 trees colour in the CIE L*a*b* space (L* lightness, a* red/green axis, b* yellow/blue axis), extractives content (acetone and hot-water extractives, amount of phenolics) and the brown-rot decay resistance were determined. For calculating the relative decay resistance ( x), mass loss after inoculation for 16 weeks with two fungi [ Coniophora puteana (Schum.ex.Fr.) Karst., Poria placenta (Fr.) Cke, European standard EN 113] of larch heartwood samples was compared to Scots pine ( Pinus sylvestris L) sapwood reference samples (EN 350-1). Different species [Japanese larch ( Larix kaempferi Lamb.), Hybrid larch (Larix deciduax L. kaempferi) and European larch ( L. decidua Mill.)], provenances and age classes (38-year, >150-year) were included. Japanese larch heartwood turned out to be significantly more reddish (higher a*-values) compared to the European larch provenances. Reddishness of the hybrids was intermediate. The red hue (+a*) was strongly correlated with the amount of phenols ( r =0.84) and decay resistance ( r =0.63) and therefore suitable for prediction of both parameters. The results suggest that colour measurements of larch heartwood could be of benefit in tree breeding programs and for an optimised utilization of larch timber.     

Diet selection of the southern vizcacha (<Emphasis Type="Italic">Lagidium viscacia</Emphasis>): a rock specialist in north western Patagonian steppe,Argentina

The southern vizcacha (Lagidium viscacia) is a rock specialist that inhabits small colonies in isolated rocky outcrops of northwestern Patagonia. This study analyzes its diet selection in relation to food availability, establishes the degree of dietary specialization, and discusses the potential competition with exotic herbivores. Diet composition and food availability were determined in summer and winter in eight rocky outcrops by microhistological analysis of fecal pellets, and food availability was estimated by the Braun Blanquet cover abundance scale. Vegetation cover differences were detected by using a random analysis of variance (ANOVA) factorial block design, and dietary preferences were determined by the confidence interval of Bonferroni. The southern vizcacha showed a specialized feeding behavior despite the consumption of a wide variety of items. Their diet was concentrated on a few types of food, mainly grasses, and the trophic niche was narrow and without seasonal variations. In winter, when food was scarce and of lower quality than summer, diet was dominated by Stipa speciosa, suggesting a selection according to the selective quality hypothesis. Our results (narrow trophic niche, restricted activity near rocky outcrops, and a diet with high proportions of low-quality grasses) showed that the vizcacha is an obligatory dietary specialist, and these characteristics made it highly vulnerable to changes in food availability. In this scenario, overgrazing caused by alien species with similar diets, as the European hare and livestock, could negatively affect their colonies.     

Ice‐age persistence and genetic isolation of the disjunct distribution of larch in Alaska

Larix laricina (eastern larch, tamarack) is a transcontinental North American conifer with a prominent disjunction in the Yukon isolating the Alaskan distribution from the rest of its range. We investigate whether in situ persistence during the last glacial maximum (LGM) or long‐distance postglacial migration from south of the ice sheets resulted in the modern‐day Alaskan distribution. We analyzed variation in three chloroplast DNA regions of 840 trees from a total of 69 populations (24 new sampling sites situated on both sides of the Yukon range disjunction pooled with 45 populations from a published source) and conducted ensemble species distribution modeling (SDM) throughout Canada and United States to hindcast the potential range of L. laricina during the LGM. We uncovered the genetic signature of a long‐term isolation of larch populations in Alaska, identifying three endemic chlorotypes and low levels of genetic diversity. Range‐wide analysis across North America revealed the presence of a distinct Alaskan lineage. Postglacial gene flow across the Yukon divide was unidirectional, from Alaska toward previously glaciated Canadian regions, and with no evidence of immigration into Alaska. Hindcast SDM indicates one of the broadest areas of past climate suitability for L. laricina existed in central Alaska, suggesting possible in situ persistence of larch in Alaska during the LGM. Our results provide the first unambiguous evidence for the long‐term isolation of L. laricina in Alaska that extends beyond the last glacial period and into the present interglacial period. The lack of gene flow into Alaska along with the overall probability of larch occurrence in Alaska being currently lower than during the LGM suggests that modern‐day Alaskan larch populations are isolated climate relicts of broader glacial distributions, and so are particularly vulnerable to current warming trends.     

Natural regeneration patterns of the introduced larch, Larix kaempferi (Pinaceae), on the volcano Mount Koma, northern Japan

The 1929 eruption of Mount Koma (1140 m in altitude) completely deforested the vegetation on the summit area of the volcano. An alien species of larch, Larix kaempferi (=L. leptolepis) was planted on the lower slopes of the volcano between 1953 and 1963, but since then has become abundant on the summit. To determine the regeneration patterns of the larch, we measured stem densities on aerial photographs taken in 1963, 1973 and 1994, and in the field during 1996. Larix kaempferi stems with crown diameters > 2 m were mapped on aerial photographs divided into 1083 100 m×100 m grids. Stem densities on the summit increased from 0.8/ha in 1963, to 14.1/ha in 1994. Willows and birches also established there but did not grow as large as the larch. All these species are wind dispersed, and larch densities were higher in areas closer to the plantations, suggesting that wind intensity and direction determined seed migration. Four environmental factors—slope gradient, direction, elevation, and distance from the plantations in each grid—were correlated with larch stem densities. Multiple regression showed that establishment patterns of L. kaempferi in the early stages were mainly related to distance from seed source (the plantations). Later, geographical disturbances and/or physiological stresses became more important. Density effects on tree invasion have been weak until now. We concluded that revegetation primarily depends on the chance of seed immigration, and that the larches may be an earlier successional species than any other native tree species.     

Heartwood extractives and lignin content of different larch species (<Emphasis Type="Italic">Larix </Emphasis>sp.) and relationships to brown-rot decay-resistance

The extractive content of lignin and the brown-rot decay-resistance against Coniophora puteana and Poria placenta were studied in larch heartwood from different species and origin (Larix decidua var. decidua, L. decidua var. sudetica, L. kaempferi , L. × eurolepis). The study material consisted of 106 trees from a 39-year old provenance trial in France. The hot-water-soluble extractives were very variable (from5.66% to 20.50% of dry weight), but there was no significant variation between the investigated species and origins. In contrast, acetone extractives, the total amount of phenolics and lignin showed significant differences. The concentration of phenolics and lignin was significantly higher in L. kaempferi and in L. × eurolepis than in L. decidua. The total phenolics content was strongly correlated with decay-resistance in all investigated larch origins. A higher concentration of phenolics goes hand in hand with higher decay resistance and phenolics might therefore be a promising parameter to rapidly evaluate the level of decay-resistance in larch.