Influence of host log age and refuge from natural enemies on colonization and survival of Phoracantha semipunctata

The pine cone weevil, Pissodes validirostris Gyll. (Coleoptera: Curculionidae), attacks seed cones of most Eurasian pine species, except these of Swiss stone pine (Pinus cembra L.). Behavioural responses of adult weevils to cone volatile emissions of Swiss stone pine and to those of a common host, mountain pine (Pinus uncinata Ram.), were compared in an olfactometer. Weevils were significantly attracted by the volatile blend emitted by mountain pine, but Swiss stone pine volatiles elicited an inverse response, with most weevils moving in the opposite direction to the odour source. However, the majority of second instar weevil larvae that were extracted from mountain pine cones and transferred into Swiss stone pine cones were capable of developing to the adult stage. This suggests that Swiss stone pine cones do not contain strong feeding deterrents that could prevent larval development. The possible factors involved in the absence of colonization of Swiss stone pine cones by cone weevils are discussed.     

Allozyme polymorphism of Swiss stone pine Pinus cembra L. in mountainous populations of the Alps and the Eastern Carpathians

Swiss stone pine Pinus cembra L. is a species with fragmented range, occurring in the Alpine-East Carpathian mountain system. Seeds of P. cembra are dispersed by nutcrackers, which offers potential possibilities for gene exchange among populations. Using isozyme analysis, we have examined five samples from two parts of the Swiss stone pine range: the Alps (Switzerland and Austria) and the Carpathians (two samples from the northern macroslope of the Gorgany Ridge, Eastern Carpathians, Ivano-Frankovsk oblast and one sample from Trans-Carpathian oblast of Ukraine). The allele frequencies of 30 isozyme loci, coding for enzymes ADH, FDH, FEST, GDH, GOT, IDH, LAP, MNR, MDH, PEPCA, 6PGD, PGI, PGM, SDH, SKDH, SOD, were analyzed using cluster analysis and methods of principal components. Two clusters, corresponding to the isolated Alpine and Carpathian parts of the range, were found. The main contribution to these differences were made by loci Adh-1, Adh-2, Fest-2, Lap-3, Mdh-4, and Sod-4. The interpopulation differentiation proved to be somewhat higher than that typical for pines (F(ST) = 7.4%), but within the limits characteristic for taxonomically close species. Thus, isolation of the populations did not lead to their marked differentiation, which may be explained by gene flow and balancing selection, which equalizes gene frequencies across the fragmented species area. Interlocus F(ST) heterogeneity (from 0.003 to 0.173) suggests adaptive significance of some of the allozyme polymorphisms or linkage of some loci with adaptive genes. The Carpathian populations were shown to have higher gene diversity than the Alpine ones (expected heterozygosities 0.095-0.114 and 0.060-0.080, respectively). A deficit of heterozygotes (as compared to the Hardy-Weinberg proportions), observed in the embryo sample, was probably explained by inbreeding. The reduction in the area of Carpathian pine forests in Holocene, caused by the global climatic changes and the anthropogenic impact, is hazardous for the gene pool of the species. The maintenance of genetic uniqueness of both Carpathian populations of P. cembra in general, and individual stands in particular, requires special measures for protection of Swiss stone pine in the Eastern Carpathians.     

Potential invasion of China by exotic insect pests associated with tree seeds

A total of 39 insect species, mostly seed chalcids in the genus Megastigmus (Hymenoptera), but also midges (Diptera), are listed as potential seed-borne invaders of Chinese conifers. Although the number of native seed insects per conifer genus does not differ between China and other biogeographical regions, there are significantly fewer seed insects associated with each conifer genus in China than potential invaders. The eventual success of the invaders is likely to depend on the presence of native Chinese conifers that are congeneric with the original host, or on the presence of the original host as an exotic. When a substantial entomofauna is already associated with cones, competition for seed resources may limit the potential impact of invaders because seed insects are usually the last organisms to colonize the cone. A survey of 26 fir species, both native and introduced to Europe, showed that overall seed infestation by five species of exotic chalcids is negatively correlated to levels of damage by native insects, except on the original hosts of the chalcids. Similar patterns are hypothesized for native firs, spruces, Douglas firs, and larches in China. Uncontrolled importation of seeds and nuts of broad-leaved trees could also facilitate the introduction of seed chalcids, seed bruchids, tortricid moths and nut weevils into China. Only six species of seed chalcids are present in China, out of the 72 known to attack broad-leaved seeds over the world.     

Larch- and pine-feeding host races of the larch bud moth (Zeiraphera diniana) have cyclic and synchronous population fluctuations

Population cycles of many forest-defoliating insects often show synchronous fluctuations at both intra-specific (spatial synchrony) and inter-specific levels. However, population dynamics of different host-associated biotypes of the same species, such as those of the larch budmoth (LBM), Zeiraphera diniana (Lepidoptera: Tortricidae), have never been compared. This species causes extensive defoliation of larch forests every 8 to 9 years in the Alps, but it consists of two genetically-differentiated host races, the first one developing on European larch, Larix decidua , and the other one developing on Swiss stone pine, Pinus cembra . The dynamics of Zeiraphera populations have been extensively studied on larch, whereas little is known about larval density and possible population fluctuations on sympatric pines. A larval census on Swiss stone pine was conducted in the Swiss Alps intermittently between 1958 to 2004 and in the French Alps from 1992 to 2004. Population density of Zeiraphera on pine varied up to 5000-fold and showed periodic oscillations, with five peaks in Switzerland and one in France. Because the feeding activity of the pine race is restricted to the elongating shoot of the current year, no conspicuous defoliation of pine trees was noted during years of high larval densities. Zeiraphera populations on pine oscillated in significant synchrony with larch-associated populations, and peak densities were observed either the same year or shifted by±one year. Our results did not allow any explanation for cyclic fluctuations of LBM on pine, but the synchrony with the larch race's cycle suggests that studies on genetics as well as on parasitism should be intensified.     

Performance of the fir coneworm Dioryctria abietivorella (Grote) as affected by host species and presence or absence of seed cones

1 Larval performance of Dioryctria abietivorella (Grote) (Lepidoptera: Pyralidae) was compared when insects were reared in white spruce, black spruce and Jack pine seed orchards. For each species, half of the insects developed in the presence of cones, while the other half was maintained on branches without cones. 2 Significantly faster development rates were observed on spruce species when compared to Jack pine. Significant differences in survival were also recorded between the different feeding treatments. 3 The presence of seed cones on spruce species significantly increased insect mean weight compared with branches without cones, but no significant differences were noticed between the different tree species with cones. 4 White spruce is the most suitable host tree for fir coneworm feeding and the availability of seed cones plays an important role in determining D. abietivorella larval performance.     

油松球果小卷蛾成虫的产卵选择

油松球果小卷蛾Gravitarmata margarotana(Heinemann)是广泛分布的一种松属球果和枝梢害虫,在我国北方油松良种基地主要危害油松球果。用油松和华山松球果做产卵选择试验,以及2树种球果浸提液对产卵影响的结果表明,油松球果对产卵雌虫具有更强的引诱作用;不同油松球果类型的着卵量结果表明,红色球果类型的着卵量显著高于绿色球果类型,并且同一颜色球果,有刺类型的着卵量多于无刺类型。球果挥发成分结果表明,油松球果挥发成分有6个组分,而华山松球果挥发成分只有5个组分,与油松球果相比,无β-非兰烯组分;油松不同株系类型球果挥发成分只表现出含量上的差异。     

Host-plant influence on the population ecology of the jack pine budworm, Choristoneura pinus (Lepidoptera: Tortricidae)

Abstract.

• 1 Newly-emerged, second-instar jack pine budworm (Choristoneura pinus Freeman) establish spring feeding sites preferentially in the pollen cones of their host tree, Pinus banksiana Lamb.
• 2 Laboratory studies showed that the rate of establishment and survival of jack pine budworm on pollen cones was high throughout the entire spring emergence period of the insect.
• 3 In contrast, the rate of establishment and survival of jack pine budworm on vegetative buds was very poor early in the spring. Vegetative buds were only acceptable as feeding sites to the jack pine budworm for a relatively brief period in late spring.
• 4 Field studies showed that the change in population density of jack pine budworm during the spring emergence stage, as expressed by k-values, was a function of the abundance of pollen cones in the stand. Population reduction was greatest in those stands with the fewest pollen cones.
• 5 Direct measurement of spring dispersal by jack pine budworm showed that dispersal and consequent losses to the budworm population were greatest in stands with the fewest pollen cones.
• 6 We conclude that changes in the density of jack pine budworm are strongly influenced by production of pollen cones in the host stand. Because pollen cone production is related to previous years of defoliation by the jack pine budworm, we propose that pollen cones act as a density-dependent factor governing the density of early-stage jack pine budworm.
• 7 The resulting dynamics are compared to those of other budworm species and used to explain observed regional and temporal patterns of jack pine budworm outbreaks.

     

Cones structure and seed traits of four species of large‐seeded pines: Adaptation to animal‐mediated dispersal

Seed dispersal selection pressures may cause morphological differences in cone structure and seed traits of large‐seeded pine trees. We investigated the cone, seed, and scale traits of four species of animal‐dispersed pine trees to explore the adaptations of morphological structures to different dispersers. The four focal pines analyzed in this study were Chinese white pine (Pinus armandi), Korean pine (P. koraiensis), Siberian dwarf pine (P. pumila), and Dabieshan white pine (P. dabeshanensis). There are significant differences in the traits of the cones and seeds of these four animal‐dispersed pines. The scales of Korean pine and Siberian dwarf pine are somewhat opened after cone maturity, the seeds are closely combined with scales, and the seed coat and scales are thick. The cones of Chinese white pine and Dabieshan white pine are open after ripening, the seeds fall easily from the cones, and the seed coat and seed scales are relatively thin. The results showed that the cone structure of Chinese white pine is similar to that of Dabieshan white pine, whereas Korean pine and Siberian dwarf pine are significantly different from the other two pines and vary significantly from each other. This suggests that species with similar seed dispersal strategies exhibit similar morphological adaptions. Accordingly, we predicted three possible seed dispersal paradigms for animal‐dispersed pines: the first, as represented by Chinese white pine and Dabieshan white pine, relies upon small forest rodents for seed dispersal; the second, represented by Korean pine, relies primarily on birds and squirrels to disperse the seeds; and the third, represented by Siberian dwarf pine, relies primarily on birds for seed dispersal. Our study highlights the significance of animal seed dispersal in shaping cone morphology, and our predictions provide a theoretical framework for research investigating the coevolution of large‐seeded pines and their seed dispersers.     

The role of insects in the dynamics of cone production of red pine

Summary The mortality of red pine cones was studied for several consecutive years using life tables in eight different stands in the northern Great Lakes States. Usually less than 20% of a cohort of female flowers survived to maturity. Insects were the main source of mortality and were primarily responsible for annual fluctuations in the abundance of mature cones. Insects were probably also responsible, along with late summer weather (especially precipitation), for influencing the rate of initiation and differentiation of flower bud primordia, as shown in a model of the flowering-cone production processes. These studies suggest that the devastation of developing cone crops by insects may actually enhance flower primordia production and thus the future abundance of feeding and breeding sites for cone insects.     

Chloroplast microsatellites and mitochondrial nad1 intron 2 sequences indicate congruent phylogenetic relationships among Swiss stone pine (Pinus cembra), Siberian stone pine (Pinus sibirica), and Siberian dwarf pine (Pinus pumila)

We studied the phylogenetic relationships among the three stone pine species, Pinus cembra, P. sibirica, and P. pumila, using chloroplast microsatellites and mitochondrial nad1 intron 2 sequences. The three chloroplast microsatellite loci combined into a total of 18 haplotypes. Fourteen haplotypes were detected in 15 populations of P. cembra and one population of P. sibirica, five of which were shared between the two species, and the two populations of P. pumila comprised four species-specific haplotypes. Mitochondrial intron sequences confirmed this grouping of species. Sequences of P. cembra and P. sibirica were identical, but P. pumila differed by several nucleotide substitutions and insertions/deletions. A repeat region found in the former two species showed no intraspecific variation. These results indicate a relatively recent evolutionary separation of P. cembra and P. sibirica, despite their currently disjunct distributions. The species-specific chloroplast and mitochondrial markers of P. sibirica and P. pumila should help to trace the hybridization in their overlapping distribution area and to identify fossil remains with respect to the still unresolved postglacial re-colonization history of these two species.     

Competition Among Insects, Birds and Mammals for Conifer Steeds

Species of at least 5 orders of insects, 6 families of birds,and 2 orders of mammals, in various combinations, can exploitthe cones and seeds of most species of conifers. Lodgepole pineis the exception to this pattern of broad taxonomic diversityof seed predators in that only pine squirrels and coreid bugsattack its serotinous cones. The contrast between lodgepolepine and other conifers demonstrates that large intrinsic variationin the abundance of a resource fosters the evolution of a broadrange of taxonomic groups to exploit the resource. The diversegroups'are limited by different predators and alternate resourceswhen conifer seeds independently decrease in abundance.     

Repeated freeze–thaw cycles induce embolism in drought stressed conifers (Norway spruce,stone pine)

Freezing and thawing lead to xylem embolism when gas bubbles caused by ice formation expand during the thaw process. However, previous experimental studies indicated that conifers are resistant to freezing-induced embolism, unless xylem pressure becomes very negative during the freezing. In this study, we show that conifers experienced freezing-induced embolism when exposed to repeated freeze-thaw cycles and simultaneously to drought. Simulating conditions at the alpine timberline (128 days with freeze-thaw events and thawing rates of up to 9.5 K h(-1) in the xylem of exposed twigs during winter), young trees of Norway spruce [Picea abies (L.) Karst.] and stone pine (Pinus cembra L.) were exposed to 50 and 100 freeze-thaw cycles. This treatment caused a significant increase in embolism rates in drought-stressed samples. Upon 100 freeze-thaw cycles, vulnerability thresholds (50% loss of conductivity) were shifted 1.8 MPa (Norway spruce) and 0.8 MPa (stone pine) towards less negative water potentials. The results demonstrate that freeze-thaw cycles are a possible reason for winter-embolism in conifers observed in several field studies. Freezing-induced embolism may contribute to the altitudinal limits of conifers.     

Reproductive and genetic characteristics of rare,disjunct pitch pine populations at the northern limits of its range in Canada

Pitch pine, Pinus rigida Mill., is a rare species in Canada, existing as a disjunct population in the St. Lawrence River Valley in eastern Ontario and two northern outlier stands in southern Quebec along Canada's southern border with the United States. Reproductive and genetic characteristics of these small, scattered stands were investigated to develop a foundation for management and restoration in the event of range expansion northwards under anticipated climate warming. Seed yields and seed quality appear to be comparable to other eastern conifers, and to pitch pine at the center of its geographic range. For seed and seedling growth traits, most of the variation was attributable to differences among trees within stands and, to a lesser extent, among stands within a population; whereas the population effect was non-significant. For reproductive traits, such as numbers of filled and empty seeds per cone, reproductive efficiency, and inbreeding estimates, high levels of variation (ranging from 26% to 33%) were found among stands, suggesting that stand structural features, such as stand size and tree density within stands, play an important role in pollination environment and overall reproductive success. Estimates of genetic diversity at 32 allozyme gene loci indicate that these small, isolated stands have maintained relatively high levels of genetic diversity compared with populations at the center of its geographic range, and also relative to other widely dispersed eastern conifers. The relatively high levels of viable seed production and genetic diversity in native pitch pine populations indicate that native Canadian populations may be suitable seed sources for species restoration and range expansion in Canada.     

Great spotted woodpeckers Dendrocopos major exert multiple forms of phenotypic selection on Scots pine Pinus sylvestris

Relatively few animal species extract seeds from closed conifer cones because of the forces required to spread apart or penetrate the woody scales. Those species that forage on seeds in closed cones tend to forage selectively, and therefore act as selective agents on cone structure. However, little is known about the foraging preferences and thus phenotypic selection that is exerted on conifers by many species that forage extensively on seeds in closed cones, including especially woodpeckers (Picidae). Great spotted woodpeckers Dendrocopos major are one of the main predators of seeds in closed cones of Scots pine Pinus sylvestris in central and eastern Europe. To estimate the cone preferences of these woodpeckers foraging on Scots pine, we contrasted traits of cones that were and were not foraged on by woodpeckers. Woodpeckers preferred to forage on shorter cones when scales were thin (smaller apophyses) but preferred cones of intermediate length when scales were thicker, providing evidence for correlational selection. The preference for intermediate‐sized cones indicates that woodpeckers exert disruptive selection on cone length when cones have thicker scales, but the overall selection on cone length across all scale types indicates directional favoring the evolution of longer cones. Woodpeckers avoided cones with thicker scales, which would lead to directional selection favoring the evolution of thicker scales. Preferences for intermediate‐sized cones have been found in tree squirrels and directional selection favoring the evolution of cones with thicker scales may be a common outcome of the foraging behavior of birds.     

Can the emergence of pine Diplodia shoot blight in France be explained by changes in pathogen pressure linked to climate change?

Sphaeropsis shoot blight, caused by Diplodia pinea and Diplodia scrobiculata, damage conifers throughout the world. In France, the first disease outbreaks were reported during the 1990s. The factors associated with the pathogen presence in stands and the relationship between pathogen and disease distributions were analysed in order to understand the Sphaeropsis emergence. Eighty‐two stands of Pinus nigra, Pinus sylvestris, Pinus pinaster and Pinus radiata were visited. Cones were collected on the ground to assess the pathogen frequency. Diplodia spp were isolated and determined by a species‐specific PCR test. The role of potential explaining factors of D. pinea prevalence on cones was analysed by logistic regression. D. pinea was the dominant species in visited stands. The main factors influencing the pathogen presence selected in the models were host species (the pathogen being less frequent on P. pinaster than on P. nigra and P. sylvestris cones), winter temperature and summer rain, which were both positively correlated with cone colonization. The climate became more favourable to D. pinea presence within the last 15 years compared with the previous 30‐year period. By contrast, future climatic changes over the next 40 years should have far less impact on the pathogen presence.     

Allozyme Polymorphism of Swiss Stone Pine <Emphasis Type="Italic">Pinus cembra</Emphasis> L. in Mountain Populations of the Alps and the Eastern Carpathians

Swiss stone pine Pinus cembra L. is a species with fragmented range, occurring in the Alpine-East Carpathian mountain system. Seeds of P. cembra are dispersed by nutcrackers, which offers potential possibilities for gene exchange among populations. Using isozyme analysis, we have examined five samples from two parts of the Swiss stone pine range: the Alps (Switzerland and Austria) and the Carpathians (two samples from the northern macroslope of the Gorgany Ridge, Eastern Carpathians, Ivano-Frankivs'ka oblast and one sample from Zakarpats'ka oblast of Ukraine). The allele frequencies of 30 isozyme loci, coding for enzymes ADH, FDH, FEST, GDH, GOT, IDH, LAP, MNR, MDH, PEPCA, 6-PGD, PGI, PGM, SDH, SKDH, SOD, were analyzed using cluster analysis and Principal Component Analysis. Two clusters, corresponding to the isolated Alpine and Carpathian parts of the range, were found. The main contribution to these differences were made by loci Adh-1, Adh-2, Fest-2, Lap-3, Mdh-4, and Sod-4. The interpopulation differentiation proved to be somewhat higher than that typical for pines (F_ST = 7.4%), but within the limits characteristic for taxonomically close species. Thus, isolation of the populations did not lead to their marked differentiation, which may be explained by gene flow and balancing selection, which equalizes gene frequencies across the fragmented species area. Interlocus (F_ST heterogeneity (from 0.003 to 0.173) suggests adaptive significance of some of the allozyme polymorphisms or linkage of some loci with adaptive genes. The Carpathian populations were shown to have higher gene diversity than the Alpine ones (expected heterozygosities 0.095–0.114 and 0.060–0.080, respectively). A deficiency of heterozygotes (as compared to the Hardy-Weinberg proportions), observed in the embryo sample, was probably explained by inbreeding. The reduction in the area of Carpathian pine forests in Holocene, caused by the global climatic changes and the anthropogenic impact, is hazardous for the gene pool of the species. The maintenance of genetic uniqueness of both Carpathian populations of P. cembra in general, and individual stands in particular, requires special measures for protection of Swiss stone pine in the Eastern Carpathians.     

Linking patterns and processes of species diversification in the cone flies Strobilomyia (Diptera: Anthomyiidae)

Phytophagous insects provide useful models for the study of ecological speciation. Much attention has been paid to host shifts, whereas situations where closely related lineages of insects use the same plant during different time periods have been relatively neglected in previous studies of insect diversification. Flies of the genus Strobilomyia are major pests of conifers in Eurasia and North America. They are specialized feeders in cones and seeds of Abies (fir), Larix (larch) ,and Picea (spruce). This close association is accompanied by a large number of sympatric Strobilomyia species coexisting within each tree genus. We constructed a molecular phylogeny with a 1320 base-pair fragment of mitochondrial DNA that demonstrated contrasting patterns of speciation in larch cone flies, as opposed to spruce and fir cone flies; this despite their comparable geographic distributions and similar resource quality of the host. Species diversity is the highest on larch, and speciation is primarily driven by within-host phenological shifts, followed by allopatric speciation during geographical expansion. By contrast, fewer species exploit spruce and fir, and within-host phenological shifts did not occur. This study illustrates within-host adaptive radiation through phenological shifts, a neglected mode of sympatric speciation.     

Effects of different insect species on seed quantity and quality in Norway spruce

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Insect community response to switchgrass intercropping and stand age of loblolly pine (Pinus taeda) plantations

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Geographical matching of volatile signals and pollinator olfactory responses in a cycad brood-site mutualism

Brood-site mutualisms represent extreme levels of reciprocal specialization between plants and insect pollinators, raising questions about whether these mutualisms are mediated by volatile signals and whether these signals and insect responses to them covary geographically in a manner expected from coevolution. Cycads are an ancient plant lineage in which almost all extant species are pollinated through brood-site mutualisms with insects. We investigated whether volatile emissions and insect olfactory responses are matched across the distribution range of the African cycad Encephalartos villosus. This cycad species is pollinated by the same beetle species across its distribution, but cone volatile emissions are dominated by alkenes in northern populations, and by monoterpenes and a pyrazine compound in southern populations. In reciprocal choice experiments, insects chose the scent of cones from the local region over that of cones from the other region. Antennae of beetles from northern populations responded mainly to alkenes, while those of beetles from southern populations responded mainly to pyrazine. In bioassay experiments, beetles were most strongly attracted to alkenes in northern populations and to the pyrazine compound in southern populations. Geographical matching of cone volatiles and pollinator olfactory preference is consistent with coevolution in this specialized mutualism.