Biology and host associations of redbay ambrosia beetle (Coleoptera: Curculionidae: Scolytinae), exotic vector of laurel wilt killing redbay trees in the southeastern United States

The redbay ambrosia beetle, Xyleborus glabratus Eichhoff (Coleoptera: Curculionidae: Scolytinae), and its fungal symbiont, Raffaelea sp., are new introductions to the southeastern United States responsible for the wilt of mature redbay, Persea borbonia (L.) Spreng., trees. In 2006 and 2007, we investigated the seasonal flight activity of X. glabratus, its host associations, and population levels at eight locations in South Carolina and Georgia where infestations ranged from very recent to at least several years old. Adults were active throughout the year with peak activity in early September. Brood development seems to take 50-60 d. Wood infested with beetles and infected with the Raffaelea sp. was similar in attraction to uninfested redbay wood, whereas both were more attractive than a nonhost species. Sassafras, Sassafras albidium (Nutt.) Nees, another species of Lauraceae, was not attractive to X. glabratus and very few beetle entrance holes were found in sassafras wood compared with redbay. Conversely, avocado, Persea americana Mill., was as attractive to X. glabratus as swampbay, P. palustris (Raf.) Sarg., and both were more attractive than the nonhost red maple, Acer rubrum L. However, avocado had relatively few entrance holes in the wood. In 2007, we compared X. glabratus populations in areas where all mature redbay have died to areas where infestations were very active and more recent. Trap catches of X. glabratus and numbers of entrance holes in trap bolts of redbay were correlated with the number of dead trees with leaves attached. Older infestations where mature host trees had been eliminated by the wilt had low numbers of beetles resulting in trap catches ranging from 0.04 to 0.12 beetles per trap per d compared with 4-7 beetles per trap per d in areas with numerous recently dead trees. Our results indicate beetle populations drop dramatically after suitable host material is gone and provide hope that management strategies can be developed to restore redbay trees. The lack of attraction of X. glabratus to sassafras suggests that spread of X. glabratus may slow once it is outside the range of redbay.     

Factors affecting the survival of ash (Fraxinus spp.) trees infested by emerald ash borer (Agrilus planipennis)

Emerald ash borer (Agrilus planipennis) (EAB), an Asian woodboring beetle accidentally introduced in North America, has killed millions of ash (Fraxinus spp.) trees and is spreading rapidly. This study examined the effects of tree- and site-level factors on the mortality of ash trees in stands infested by EAB in OH, USA. Our data show that ash populations in forested sites can progress from healthy to almost complete mortality of mature trees within 6 years. Although the end result of nearly complete mortality does not vary, survival analysis with 5 years of data showed that some factors affected the rate of mortality. We found more rapid mortality in stands with lower densities of ash trees. This finding supports an extension of the resource dilution hypothesis whereby concentration of EAB on few trees in low ash density areas leads to rapid decline of these trees. This contradicts an extension of the resource concentration theory that greater host density increases relative pest abundance and host mortality. Although reductions in ash density via diversification may be desirable for other silvicultural, conservation, and management objectives in preparation for EAB, our study shows that the management strategy of reducing ash density is unlikely to protect the remaining ash trees. Survival analysis also showed that mortality was more rapid for trees shaded by other trees and for trees initially exhibiting dieback. In management scenarios where hazard tree removal must be spread over several years due to budget constraints, focusing initial tree removal on stressed trees is recommended.     

Effect of laurel wilt invasion on redbay populations in a maritime forest community

Invasive insects and fungal pathogens have triggered numerous declines in ecologically important tree species in the forests of eastern North America. Although now functionally extinct in many ecosystems, these tree species have been able to persist through sprouting or the presence of a low density of resistant individuals. In this study, we document widespread mortality of another dominant North American hardwood species, redbay (Persea borbonia, Lauraceae), from an exotic disease, laurel wilt. This disease is caused by a nonnative Asian ambrosia beetle, Xyleborus glabratus, and its pathogenic fungal symbiont, Raffaelea lauricola, which were introduced to Georgia, USA in 2003. We conducted tree surveys on an island near the center of introduction from 2004 to 2009 and assessed the trajectory of tree mortality caused by laurel wilt. Additionally, we examined sprouting as a mechanism for persistence and whether changes in community structure occurred after laurel wilt introduction. We observed 98 % death of main stems and widespread mortality of genets (79 %) independent of main stem size. All remaining individuals were symptomatic of laurel wilt. Sprouting does not appear to give redbay the ability to maintain genets and recruit new stems into the forest canopy. We identified a negative interaction between laurel wilt and deer browse on stems and new sprouts, which may accelerate death rates of infected populations. If our results are applicable across redbay’s geographic range, a once abundant tree species may become ecologically extinct from coastal forest ecosystems in the southeastern United States.     

The Imperial Palm (Roystonea oleracea (Jacq.) O.F. Cook) as an invasive species of a wetland in Brazilian Atlantic forest

The aim of this research was to study the population structure of an exotic palm, Roystonea oleracea (Arecaceae), map its spatial distribution and investigate its invasive status in an Atlantic forest wetland. A total of 130 live and 7 dead standing palms ≥10 cm DBH were sampled. Data showed a trend towards population expansion, with most seedlings and saplings occurring within a radius of ~12 m from the mother plants but some larger trees (DBH >10 cm) up to 440 m from the parents. This exotic species is established and has the potential to become invasive, especially near wetlands. Its control or eradication should be undertaken and we suggest the immediate removal of reproductive individuals, and constant monitoring of young individuals leading to their future removal. Use of this species as an ornamental should be made with care to prevent or reduce possible harmful effects of this exotic and potentially invasive species in Brazilian wetlands.     

New method for rapidly estimating population densities of the concealed wood‐borer Monochamus alternatus (Coleoptera: Cerambycidae) in the field

To rapidly estimate pine sawyer, Monochamus alternatus Hope, population densities in forests, the vertical distributions of M. alternatus oviposition sites and larvae on infested Masson pines (Pinus massoniana Lamb.) were studied. Results showed that the number of oviposition sites on sections of trunks between 0 and 2 m above ground was significantly greater than on sections of trunk above 2 m, and the vertical distribution had a significant logarithmic relationship with trunk height. The larval number of M. alternatus on dead infested trees had a significant difference among heights of trunks. Sections on trunks at 2–4 m usually contained the largest number of M. alternatus larvae, while the number of larvae on trunks above 10 m declined significantly, as well as in the 1 m section of trunk at the base. The vertical distribution of M. alternatus larvae on dead infested pines showed a distinct parabolic relationship with trunk height. The number of oviposition sites of M. alternatus on infested Masson pine trunks revealed a significant exponential relationship with the diameter at breast height (DBH) of trees. A significant positive linear relationship also was observed between M. alternatus larval number and DBH on the host pine trees, as well as between the numbers of larvae and oviposition sites on an individual tree. The total number of larvae in an infested tree could be calculated easily using an established equation, through counting the number of oviposition sites at 3–4 m of trunk aboveground. This study developed a practical method for rapid estimation of M. alternatus populations.     

Fine root dynamics in a Norway spruce forest (Picea abies (L.) Karst) in eastern Sweden

The annual dynamics of live and dead fine roots for trees and the field layer species and live/dead ratios were investigated at a coniferous fern forest (Picea abies L. Karts) in Sweden. Our methods of estimating the average amount of fine roots involved the periodic sampling of fine roots in sequential cores on four sampling occasions. The highest live/dead ratio was found in the upper part of the humus layer for both tree and field-layer species and decreased with depth. Most tree fine roots on the four sampling occasions were found in the mineral soil horizon, where 86, 81, 85 and 89% of <1 mm and 89, 88, 89 and 92% of <2 mm diameter of the total amounts of live fine roots in the soil profile were found. The mean amounts of live fine roots of tree species for the total soil profile on the four sampling occasions was 317, 150, 139 and 248 g m^?2 for <1 mm and 410, 225, 224 and 351 g m^?2 for <2 mm diameter fine roots. The related amount of dead fine roots was 226, 321, 176 and 299 g m^?2 and 294, 424, 282 and 381 g m^?2, respectively. Average amounts of live and dead fine-roots and live/dead ratios from other Picea abies forest ecosystems were within the range of our estimates. The production of fine roots, <1 and <2 mm in diameter, estimated from the annual increments in live fine roots, was 207 and 303 g m^?2. The related accumulation of dead fine roots was 257 and 345 g m^?2, The turnover rate of tree fine roots <1 mm in diameter in the total soil profile amounted to 0.7 yr^?1 for live and 0.8 yr^?1 for dead fine roots. The related turnover rates for tree fine roots <2 mm were 0.4 yr^?1 and 0.7 yr^?1. Our data, although based on minimum estimates of the annual fluxes of live and dead fine roots, suggests a carbon flow to the forest soil from dead fine-roots even more substantial than from the needle litter fall. Fine-root data from several Picea abies forest ecosystems, suggest high turnover rates of both live and dead tree fine-roots.     

Ash (Fraxinus spp.) mortality,regeneration, and seed bank dynamics in mixed hardwood forests following invasion by emerald ash borer (Agrilus planipennis)

Emerald ash borer (EAB; Agrilus planipennis) has killed millions of ash trees and threatens ash throughout North America, and long-term persistence of ash will depend on the potential for regeneration. We quantified ash demography, including mortality and regeneration, of Fraxinus americana (white ash), Fraxinus pennsylvanica (green ash), and Fraxinus nigra (black ash) in mixed hardwood forests near the epicenter of the EAB invasion in southeastern Michigan and throughout Ohio. Plots were established across a gradient of ash densities. Ash was the most important species in hydric sites, and ranked second among all species in mesic and xeric sites. In sites nearest the epicenter in Michigan, ash mortality exceeded 99 % by 2009, and few or no newly germinated ash seedlings were observed, leaving only an “orphaned cohort” of established ash seedlings and saplings. As ash mortality increased, the number of viable ash seeds in soil samples decreased sharply, and no viable seeds were collected in 2007 or 2008. In Ohio sites farther from the epicenter, densities of new ash seedlings were much higher in plots with healthy ash trees compared to plots where trees had died. EAB was still present in low densities in Michigan and Ohio stands in 2012 where average mortality of ash was nearly 100 %. The future of ash at these sites will depend on the outcome of the dynamic interaction between the orphaned cohort of previously established ash seedlings and saplings and low density EAB populations.     

Effects of altitude and competition on growth and mortality of the conifer Abies sachalinensis

Altitudinal gradients are convenient subjects to investigate plant responses to air temperature. Plant growth and mortality are also affected by competition at any altitude. This study investigated the effects of altitude and competition on absolute diameter growth rate (ADGR) and mortality of the conifer Abies sachalinensis by using 13-year data. This study was done at two altitudes (200 and 1,000 m a.s.l.) in northern Japan. Local crowding by conifers and broad-leaved trees reduced ADGR of target trees. ADGR was lower in high altitude than low altitude at any DBH and any degree of local crowding because of the short growing season. Observed size-dependent mortality was a U-shaped pattern against DBH at the two altitudes. Smaller and larger trees tended to die of suppression (standing-dead) and disturbances (stem-broken and uprooting), respectively. Mortality of standing-dead trees was negatively correlated with ADGR, irrespective of altitude, i.e., ADGR was a good predictor of mortality. Thus, mortality of standing-dead trees was estimated to be greater at high altitude than low altitude at any degree of local crowding because ADGR was lower at high altitude than low altitude. By contrast, mortality due to disturbances was slightly greater at low altitude than high altitude. Thus, this study showed that a short growth period decreases growth and increases mortality due to suppression at high altitude. Although global warming may increase growth and survival of individual trees at high altitude by prolonging the growth period, prediction on mortality due to disturbances needs caution because the mortality is largely affected by frequency and intensity of disturbances.     

Changes in the regional abundance of hemlock associated with the invasion of hemlock woolly adelgid (Adelges tsugae Annand)

Since its introduction, the non-native hemlock woolly adelgid (Adelges tsugae) has spread to infest hemlock (Tsuga spp.) in at least 18 states in the eastern USA. Previous studies have documented highly variable rates of hemlock mortality among infested stands making it difficult to estimate regional impacts. Here data from the US Forest Service Forest Inventory and Analysis program collected from 432 eastern U.S. counties reveals several surprising and conflicting regional patterns. First, median live and dead hemlock basal area has generally increased over the last two decades across the eastern U.S. This has generally been the case in both infested and uninfested counties. Second, the median percentage of hemlock which is alive has decreased over the past ~20 years, again in both infested and uninfested counties. Third, the ages of infestations are negatively correlated with the percentage of live hemlock, as might be expected given the known impact adelgids can have on a stand through time; however this relationship depends on the exclusion of uninfested counties, as counties infested >12 years and uninfested counties have similar percentages of live hemlock. Combined, these data suggest increasing tree density associated with the past century of reforestation and succession in the eastern U.S. may currently be overwhelming the negative impacts of the adelgid at the regional scale, however, the long-term stability of this situation is not known, and data from long-infested counties suggest the landscape may be at a “tipping point”.     

Timelapse scanning reveals spatial variation in tomato (Solanum lycopersicum L.) root elongation rates during partial waterlogging

Aims

Effects of soil amendments with crop residues on suppression of damping-off of sugar beet were examined by growing the seedlings in pasteurized, Rhizoctonia solani (AG2-2 IIIB)-infested soil at different temperatures. Dried residues of five dasheen or taro (Colocasia esculenta (L.) Schott) cultivars were compared with those of peanut (Arachys hypogaea L.) and Brassica rapa Olsson for their effects on disease suppression.

Methods and Results

When the seedlings were grown at 17/12 °C (day/night), all residues equally suppressed the disease when amended into the soil just before sowing. At 22/17 or 32/27 °C, damping-off developed in non-treated soil within 10 days, and differential suppressive effects by the residues became apparent by 21 days. When non-pasteurized, non-treated soil was infested with the pathogen, seedling survival was markedly better than in the same but pasteurized, infested soil. Yet, the effect was not different within the entire temperature ranges. Growth of both R. solani and the seedlings peaked near 25 °C and leveled off at higher temperatures.

Conclusions

These results suggest that damping-off was suppressed by antagonistic soil microorganisms, and individual residues elevated their effects differently. Under cool conditions, the antagonists dominated the pathogen to suppress the disease. Under warmer conditions, pathogenesis overcame antagonism depending on the residue, resulting in differential effects of disease suppression.     

Cold tolerance and invasive potential of the redbay ambrosia beetle (<Emphasis Type="Italic">Xyleborus glabratus</Emphasis>) in the eastern United States

Native Lauraceae (e.g. sassafras, redbay) in the southeastern USA are being severely impacted by laurel wilt disease, which is caused by the pathogen Raffaelea lauricola T. C. Harr., Fraedrich and Aghayeva, and its symbiotic vector, the redbay ambrosia beetle (Xyleborus glabratus Eichhoff). Cold temperatures are currently the only viable limitation to the establishment of X. glabratus in northern populations of sassafras. The observed lower lethal temperature of X. glabratus (? 10.0 °C) is warmer than its supercooling point (? 22.0 °C), indicating the beetle is a freeze intolerant and chill susceptible species. Empirically derived X. glabratus lower lethal temperature thresholds were combined with host distribution and microhabitat-corrected climate data to produce species distribution models for X. glabratus in the eastern USA. Macroclimate data (30-year mean annual minimum temperature) were corrected (? 1.2 °C) to account for thermal buffering afforded to X. glabratus while living inside sassafras trees. Only 0.1% of the current US sassafras spatial extent experiences sufficiently harsh winters (locales where mean annual minimum winter temperatures ≤ ? 6.2 °C for ≥ 12 h) to exclude X. glabratus establishment in our species distribution model. Minimum winter temperatures will likely cause some X. glabratus mortality in ~ 52% of the current spatial extent of sassafras, although current data do not allow a quantification of X. glabratus mortality in this zone. Conversely, ~ 48% of the current spatial extent of sassafras is unlikely to experience sufficiently cold winter temperatures to cause any significant impediment to X. glabratus spread or establishment. A modest climate change scenario (RCP4.5) of + 1.4 °C would result in 91% of the current spatial extent of sassafras in the eastern USA occurring where winter minimum temperatures are unlikely to cause any mortality to X. glabratus.     

Hollow occurrence and abundance varies with tree characteristics and among species in temperate woodland Eucalyptus

Tree hollows are a critical but diminishing resource for a wide range of fauna around the world. Conservation of these fauna depends on sustainable management of tree species that produce the hollows on which they depend. This study addressed the need for empirical data about intraspecific and interspecific variation in hollow occurrence and abundance in woodland trees in Australia. We measured and performed hollow surveys on 1817 trees of seven species of woodland Eucalyptus in central‐western New South Wales, Australia. Trees were surveyed at 51 one‐hectare sites and about 30% of trees surveyed had multiple stems. Generalized linear mixed models that accounted for nestedness of stems within trees and trees within sites detected a significant amount of variation in hollow occurrence and abundance. Models for individual tree stems of live trees showed hollow probability and abundance increased with diameter at breast height (DBH) and with increasing senescence (form). Stems of Eucalyptus microcarpa Maiden had a higher probability of having hollows than similar DBH stems of Eucalyptus camaldulensis Dehnh., Eucalyptus melliodora A.Cunn. ex Schauer or Eucalyptus populnea ssp. bimbil L.A.S.Johnson & K.D.Hill. Dead stems in live trees were more likely to have hollows than live stems of similar DBH. Each stem in a multi‐stemmed tree had a lower probability of hollow occurrence and lower abundance of hollows than single‐stemmed trees of similar DBH. For stems of dead trees, hollow occurrence and abundance increased with DBH and differed depending on stage of senescence. A comparison of our data with other studies indicates regional variation of hollow abundances within tree species.     

Production of Seeds and Cones and Consequences for Wood Radial Increment in Norway Spruce (Picea Abies (L.) Karst.)

Abstract

The presence of a trade–off between growth and reproduction was tested in four sites in a subalpine Norway spruce (Picea abies (L.) Karst.) forest by measuring annual stem diameter increments at breast height and seed and cone productions during the periods 1962–1985 and 1983–1990, respectively. Trees growing in forest stands near the timber line (about 1900 m above sea level) had the greatest reduction in annual stem diameter increment during mast years; while trees growing at about 1300–1500 m above sea level did not show any reduction. Trees growing at about 1700 m showed only a limited reduction. At the same elevation, trees growing within closed forest stands suffered a greater reduction in stem growth when compared with trees growing at the edge of a cutting.     

Tradeoffs in basal area growth and reproduction shift over the lifetime of a long-lived tropical species

Understanding of the extent to which reproductive costs drive growth largely derives from reproductively mature temperate trees in masting and non-masting years. We modeled basal area increment (BAI) and explored current growth–reproduction tradeoffs and changes in such allocation over the life span of a long-lived, non-masting tropical tree. We integrated rainfall and soil variables with data from 190 Bertholletia excelsa trees of different diameter at breast height (DBH) sizes, crown characteristics, and liana loads, quantifying BAI and reproductive output over 4 and 6 years, respectively. While rainfall explains BAI in all models, regardless of DBH class or ontogenic stage, light (based on canopy position and crown form) is most critical in the juvenile (5 cm ≤ DBH < 50 cm) phase. Suppressed trees are only present as juveniles and grow ten times slower (1.45 ± 2.73 m² year^?1) than trees in dominant and co-dominant positions (13.25 ± 0.82 and 12.90 ± 1.35 m² year^?1, respectively). Additionally, few juvenile trees are reproductive, and those that are, demonstrate reduced growth, as do reproductive trees in the next 50 to 100 cm DBH class, suggesting growth–reproduction tradeoffs. Upon reaching the canopy, however, and attaining a sizeable girth, this pattern gradually shifts to one where BAI and reproduction are influenced independently by variables such as liana load, crown size and soil properties. At this stage, BAI is largely unaffected by fruit production levels. Thus, while growth–reproduction tradeoffs clearly exist during early life stages, effects of reproductive allocation diminish as B. excelsa increases in size and maturity.     

Verbenone reduces landing of the redbay ambrosia beetle,vector of the laurel wilt pathogen,on live standing redbay trees

1. Laurel wilt is a disease that has caused extensive mortality of redbay Persea borbonia in the southeastern U.S.A. The redbay ambrosia beetle Xyleborus glabratus is the vector of the causal agent of laurel wilt, the fungus Raffaelea lauricola.
2. We tested two potential repellents to the redbay ambrosia beetle, verbenone and methyl salicylate (MeSA) in an 8‐month large‐scale experiment conducted in three locations in Florida. In each location, redbay trees were treated with a single or double application of SPLAT (Specialized Pheromone and Lure Application Technology; ISCA Technologies, Riverside, California) verbenone, as well as SPLAT with a 1:2 mix of MeSA and verbenone.
3. The MeSA + verbenone mixes did not reduce beetle captures compared with the control treatment, whereas SPLAT verbenone alone significantly reduced the number of beetles captured on sticky traps placed on redbay trees in the three locations. The reduction of beetle capture was similar regardless of one or two treatments of SPLAT verbenone. The reduction of tree death with the SPLAT verbenone treatment was not statistically significant.
4. The results of the present study suggest that trunk application of verbenone can reduce landing rates of the redbay ambrosia beetle on live redbay trees and shows promise for use in an integrated pest management strategy against laurel wilt.

     

The effect of bark thickness on host partitioning between Tetrastichus planipennisi (Hymen: Eulophidae) and Atanycolus spp. (Hymen: Braconidae), two parasitoids of emerald ash borer (Coleop: Buprestidae)

Parasitoids have recently been introduced from Asia to aid in biological control in the United States of the invasive, highly damaging, emerald ash borer, Agrilus planipennis. Three introduced parasitoids have established and field biological studies are underway to improve our understanding of niche partitioning among them. Here we report one such investigation, a field experiment conducted to determine how outer bark thickness of ash trees might affect parasitism by one introduced (Tetrastichus planipennisi) and one native parasitoid (Atanycolus spp.). We found that T. planipennisi was unable to parasitize EAB larvae in trees with outer bark thicker than 3.2 mm (>11.2-cm DBH) whereas Atanycolus spp. parasitized EAB larvae in ash trees with outer bark up to 8.8 mm thick (>57.4-cm DBH). These results suggest that establishment of, and control by T. planipennisi at release sites with only large diameter trees is less likely, and that T. planipennisi will be more effective in stands with younger trees (<12-cm DBH). Releasing T. planipennisi near the leading edge of EAB invasion may have little impact on EAB populations if many ash trees are too large. We recommend releasing T. planipennisi in stands dominated by small, early successional or regenerating ash trees. This may maximize the establishment and effectiveness of this species. This limitation of T. planipennisi for biological control of emerald ash borer suggests that other EAB parasitoids from its native range with longer ovipositors, such as Spathius galinae (Hymenoptera: Braconidae), should be sought and evaluated for possible use as EAB biocontrol agents in the US. The results of this study also suggest the importance of parasitoid guild introduction for biological control in general, and hint at possible broader implications relating to resource partitioning among native and introduced parasitoids.     

Realized pollen and seed dispersal within a continuous population of the dioecious coniferous Brazilian pine [Araucaria angustifolia (Bertol.) Kuntze]

Extensive realized pollen and seed flow across populations reduces inbreeding and spatial genetic structure (SGS) and increases the genetic diversity and effective size within populations. Inbreeding, SGS and realized patterns of pollen and seed dispersal of the dioecious, wind pollinated Araucaria angustifolia were investigated based on microsatellite loci. The study was conducted in a 7.2 ha plot established within a continuous Araucaria Forest in Southern Brazil. In the plot, all 290 adult trees were mapped, measured (diameter at breast height, dbh), sexed, sampled and genotyped. We also sampled, measured (total height), mapped and genotyped 223 juveniles. A total of 86 alleles were detected in the sample (n = 513). Adults and juveniles showed a positive and significant fixation index (minimum of 0.096), suggesting inbreeding or Wahlund effect. Juveniles presented a significant aggregated distribution which was associated with a genetic aggregation (significant SGS up to 20 m), indicating that near neighbor trees may be related due the limited seed dispersal. However, the intensity of SGS was not significantly higher among juveniles (Sp = 0.0041) than adults (Sp = 0.0026). Realized pollen and seed immigration into the plot was low (pollen = 6 %; seeds = 5 %) and the patterns of pollen and seed dispersal were similar. Pollen was dispersed over long distances (343 m), but 50 % was dispersed up to 124 m. Seeds also reached long distances (318 m), with 50 % being dispersed up to 133 m. Our results are discussed in terms of auto-ecology and the genetic conservation of A. angustifolia populations.     

Pre-treatment with salicylic acid induces phenolic responses of Norway spruce (<Emphasis Type="Italic">Picea abies</Emphasis>) bark to bark beetle (<Emphasis Type="Italic">Ips typographus</Emphasis>) attack

Keymessage

The temporal gradations of the investigated phenolics in Norway spruce bark after bark beetle (Ips typographus) attack followed the general eco-physiological concept. Treatment with salicylic acid inhibits bark beetle colonisation, alleviates the phenolic responses and activates the synthesis of condensed tannins on later sampling dates.

Abstract

Conifer bark is the target of numerous organisms due to its assimilated transport and nutrient storage functions. In the presented study, 100 mM salicylic acid (SA) was applied onto Norway spruce stems prior to being infested with bark beetles (Ips typographus L.), to study the temporal gradation of changes in condensed tannins (CT) and total phenolics (tPH) and their significance for mediating stress-tolerance. A significant accumulation of CT was monitored in untreated trees in response to progressive bark beetle infestation occurring from May onwards. In SA-treated infested trees, the CT values remained at control levels until May, but after the re-treatment of infested trees in June, the concentrations of CT rose significantly in comparison to the controls. The tPH values dropped 16 days after SA-treatment, independent of infestation, and later on remained at control level until July. In contrast, tPH contents accumulated in untreated infested trees in May, eased in June and increased again in July, when the trees were affected by the second generation of bark beetles. To sum up, in May and July when the highest beetle-flight activity was monitored the metabolic shift of phenolics within untreated infested trees differed significantly from the response of SA-treated trees. In addition, on SA-treated trees less entrance holes were monitored over the whole period of sampling when compared to untreated infested trees. These results provide evidence that SA-treatment alleviates the phenolic responses, activates the synthesis of condensed tannins and inhibits bark beetle colonisation.

     

Reconstructing the invasion history of a spreading,non-native,tropical tree through a snapshot of current distribution,sizes, and growth rates

Elucidating the invasion history of non-native species has been dependent on coarse-grain and expensive methods or long-term monitoring during which the spread may have proceeded beyond feasible control. We used the case of a relatively recent introduction and spread of the neotropical Cecropia pachystachya in Singapore to develop a method for reconstructing spatio-temporal patterns of spread through a low-cost, cross-sectional study. Size and growth rates were measured for C. pachystachya trees as well as the native Macaranga gigantea. A power-expansion exponential-decline function was a better fit than the probability density function of the log-normal distribution in describing the growth-rate to size relationship for both species. C. pachystachya trees generally grew faster (up to 5.4 ± 0.1 cm per year at 12.2 ± 0.2 cm DBH) than M. gigantea trees (up to 3.8 ± 0.2 cm per year at 11.5 ± 0.3 cm DBH). We demonstrated that the integral of the reciprocal of these growth equations provides an estimate of the age of the individuals from their size. Using the size and geographic coordinates of C. pachystachya trees from an island-wide search, we estimate that the invasion front of reproductive trees (>5 cm DBH) showed at least a 20-year lag phase from the time of initial establishment to the year 2005, before advancing exponentially at median rates between 5 and 466 m year^?1 with maximum rates of several km year^?1. The extent of occurrence expanded by nearly tenfold from 2004 to 2012. Consequently, the spatial dynamics of trees can be reproduced using ontogenetic growth functions.     

Relationships between soybean shoot nitrogen components and soybean aphid populations

Defining the relationships between soybean (Glycine max [L.] merr.) shoot nitrogen (N) components and soybean aphid (Aphis glycines Matsumura) populations will increase understanding of the biology of this important insect pest. In this 2-year field study, caged soybean plants were infested with soybean aphids (initial infestation of 0, 10, 50, or 100 aphids plant^?1) at the fifth node developmental stage. Soybean aphid populations, soybean shoot dry weight, and shoot concentrations of nitrate-N, ureide-N, and total N were measured starting at full bloom through full seed soybean development stages. Soybean aphid population as well as shoot concentration of ureide-N increased rapidly starting at full bloom, peaked at beginning seed, and dramatically decreased by full seed soybean reproductive stages. Regression analysis indicated significant relationships (P = 0.01; r = 0.71) between soybean aphid populations and shoot ureide-N concentration. Thus, soybean aphid population levels appear to coincide with shoot ureide-N concentrations in the soybean plant.