Beech Scale Insect Research Articles

Enemy release from beech bark disease coincides with upslope shift of American beech

Upslope shifts in plant distributions are often attributed to warming climate and lengthening of the growing season; however, biotic interactions may also contribute. The impacts of pests and pathogens are often sensitive to climate change and can vary along the climatic gradient associated with elevation. American beech ( Fagus grandifolia) has moved upslope throughout the northeastern United States. Meanwhile, beech growth and longevity have decreased as a result of beech bark disease (BBD), a decline disease caused by the introduced European felted beech scale insect ( Cryptococcus fagisuga) and native fungi from the genus Neonectria. Within a forested landscape spanning 250–1150 m elevation, we examined the relationships between elevation, beech demography and BBD to explore whether release from BBD at higher elevation may contribute to the upslope expansion of beech. Beech has shifted upslope at a rate of 1 m⋅year−1 coincident with lower mortality, higher recruitment, faster growth, lower BBD severity, and higher sapling densities at higher elevations. We suggest that climatic constraints on the beech scale insect at high elevations has led to a lower impact of BBD, which contributed to higher rates of beech growth, survival, and recruitment and in turn facilitated the regional upslope shift of beech.

Long-term impact of a major ice storm on tree mortality in an old-growth forest

In January 1998, eastern North America experienced the worst ice storm ever recorded, which resulted in major damage to forests throughout the region. However, we know little about the long-term effects of such a severe weather event, or how its potential interaction with other biotic factors impacted tree mortality. In this study, we investigated the long-term influence of the 1998 ice storm on tree mortality in Boisé-des-Muir ecological reserve, an old-growth forest in southern Québec (Canada). Mortality rates for four out of the five tree species studied showed a striking increase a few years after the ice storm, between 2000 and 2004. After this peak, tree mortality rates remained higher than before 1998. These results indicate a lagged and persistent effect of the ice storm on tree mortality and suggest that the tree community of Boisé-des-Muir was more severely impacted than previously reported. Tree species were differentially damaged by the ice storm, and more than 25% of all tree species lost more than half their crown. Using a Cox proportional hazard model, we evaluated the impact of different levels of initial canopy damage from the ice storm on long-term tree mortality while taking into account other important biotic factors, such as tree size, tree density, indices of species-specific competition, and the presence of the beech scale insect. Species differed in their response to the storm, suggesting fundamental differences in sensitivity to extreme weather events. In particular, eastern hop-hornbeam (Ostrya virginiana) and American beech (Fagus grandifolia) were the species most vulnerable to the ice storm, and severe canopy loss led to a large increase in mortality risk. These findings suggest that the difference in tree survival following a natural disturbance likely depends not only on the severity of the damage itself, but also on species-specific ability to repair injuries and maintain physiological processes. We also found that tree size and species-specific competition influenced tree mortality significantly but did not interact with level of canopy loss. Consequently, multiple biotic factors remain important to explain mortality even after a major disturbance and should be considered when evaluating tree mortality. Our results show that the impact of the ice storm on tree mortality was species-specific, lagged and persisted for several years after the disturbance, potentially resulting in long-term compositional changes in the forest. This underscores the necessity of conducting long-term monitoring studies to understand the complete impacts of ice storms and other extreme climatic events on forests.

Genome-wide association study identifies a major gene for beech bark disease resistance in American beech (Fagus grandifolia Ehrh.)

BackgroundThe American Beech tree (Fagus grandifolia Ehrh.), native to eastern North America, is ecologically important and provides high quality wood products. This species is susceptible to beech bark disease (BBD) and is facing high rates of mortality in North America. The disease occurs from an interaction between the woolly beech scale insect (Cryptococcus fagisuga), one of two species of the fungus Neonectria (N. faginata or N. ditissima), and American Beech trees.MethodsIn this case-control genome-wide association study (GWAS), we tested 16 K high quality SNPs using the Affymetrix Axiom 1.5 K – 50 K assay to genotype an association population of 514 individuals. We also conducted linkage analysis in a full-sib family of 115 individuals. Fisher’s exact test and logistic regression tests were performed to test associations between SNPs and phenotypes.ResultsAssociation tests revealed four highly significant SNPs on chromosome (Chr) 5 for a single gene (Mt), which encodes a mRNA for metallothionein-like protein (metal ion binding) in Fagus sylvatica. Metallothioneins represent Cys-rich metal chelators able to coordinate metal atoms and may play an important role in the resistance mechanisms against beech scale insect.ConclusionThe GWAS study has identified a single locus of major effect contributing to beech bark disease resistance. Knowledge of this genetic locus contributing to resistance might be used in applied breeding, conservation and restoration programs.

A technique to screen American beech for resistance to the beech scale insect (Cryptococcus fagisuga Lind.).

Beech bark disease (BBD) results in high levels of initial mortality, leaving behind survivor trees that are greatly weakened and deformed. The disease is initiated by feeding activities of the invasive beech scale insect, Cryptococcus fagisuga, which creates entry points for infection by one of the Neonectria species of fungus. Without scale infestation, there is little opportunity for fungal infection. Using scale eggs to artificially infest healthy trees in heavily BBD impacted stands demonstrated that these trees were resistant to the scale insect portion of the disease complex(1). Here we present a protocol that we have developed, based on the artificial infestation technique by Houston(2), which can be used to screen for scale-resistant trees in the field and in smaller potted seedlings and grafts. The identification of scale-resistant trees is an important component of management of BBD through tree improvement programs and silvicultural manipulation.

May 2014: This Month in JoVE - Bioengineering Limb Prostheses, Protecting Trees from Fungal Pathogens, and Investigating the Kinematics of Swallowing

Here's a look at what's coming up in the May 2014 issue of JoVE: The Journal of Visualized Experiments. In JoVE Environment we examine beech bark disease, which affects susceptible trees after they are attacked by the beech scale insect. When it feeds on tree bark, the insect creates small fissures that allow the causative fungal species to establish infection. In the late 1890s, the beech scale insect was accidentally brought from Europe to Nova Scotia. By the 1930s, the insects and the associated fungal disease had reached the United States, subsequently spreading across the entire northeast towards the south and Midwest. Beech bark disease can kill up to 50% of infected trees, thus threatening biodiversity in hardwood forests. To address this concern, Koch and Carey adapt a technique of artificially inoculating seedlings with beech scale eggs, and present a method for screening disease resistance and susceptibility in American beech trees. This method can help to identify resistance and susceptibility genes or to screen mature trees in the field and help minimize the environmental impact of birch bark disease. Moving on to JoVE Bioengineering, much research is devoted to improving the design and function of prosthetics. This month, Smith et al. present techniques for directly estimating the inertial properties of below-knee prosthetics. The procedure is performed with the prosthesis fully intact, which reduces the measurement time and eliminates any additional time needed to realign the prosthesis after measurements. This technique allows rapid and direct measurements of the inertial properties of below-knee prosthetics, which could potentially benefit many patients who undergo lower-limb amputations. In JoVE Clinical & Translational Medicine, Thompson et al. use coordinate mapping to analyze the pharyngeal phase of swallowing, which is a complex process that involves over 20 muscles coordinated by the autonomic nervous system. To demonstrate this technique, they examine healthy subjects, without known swallowing impairments, who undergo a modified barium swallow. In this test, an X-ray of the throat is taken while the subject ingests food or liquid containing barium. Using image analysis software, the authors record anatomical landmark coordinates during the modified barium swallow. These coordinates are then translated into kinematic variables of interest, which can be useful for studying dysphagia, or difficulty swallowing. In developing vertebrates, cranial neural crest cells (CNCCs) migrate from the dorsal neural tube to form craniofacial structures. This month in JoVE Biology, Fish and Schneider examine how these neural crest cells give rise to the wide range of beak patterns in birds. The authors head to Chinatown to obtain white Pekin duck eggs, which they grow to Hamburger-Hamilton stage 9.5. Then, they graft a quail neural fold into the mid- and anterior hindbrain of the duck embryo to generate a quail-duck chimera, or a quck. Because the quail and the duck have very different beak morphology, this quck can help uncover the mechanisms of species-specific craniofacial patterning. You've just had a sneak peek of the May 2014 issue of JoVE. Visit the website to see the full-length articles, plus many more, in JoVE: The Journal of Visualized Experiments.

Comparisons of protein profiles of beech bark disease resistant and susceptible American beech (Fagus grandifolia)

BackgroundBeech bark disease is an insect-fungus complex that damages and often kills American beech trees and has major ecological and economic impacts on forests of the northeastern United States and southeastern Canadian forests. The disease begins when exotic beech scale insects feed on the bark of trees, and is followed by infection of damaged bark tissues by one of the Neonectria species of fungi. Proteomic analysis was conducted of beech bark proteins from diseased trees and healthy trees in areas heavily infested with beech bark disease. All of the diseased trees had signs of Neonectria infection such as cankers or fruiting bodies. In previous tests reported elsewhere, all of the diseased trees were demonstrated to be susceptible to the scale insect and all of the healthy trees were demonstrated to be resistant to the scale insect. Sixteen trees were sampled from eight geographically isolated stands, the sample consisting of 10 healthy (scale-resistant) and 6 diseased/infested (scale-susceptible) trees.ResultsProteins were extracted from each tree and analysed in triplicate by isoelectric focusing followed by denaturing gel electrophoresis. Gels were stained and protein spots identified and intensity quantified, then a statistical model was fit to identify significant differences between trees. A subset of BBD differential proteins were analysed by mass spectrometry and matched to known protein sequences for identification. Identified proteins had homology to stress, insect, and pathogen related proteins in other plant systems. Protein spots significantly different in diseased and healthy trees having no stand or disease-by-stand interaction effects were identified.ConclusionsFurther study of these proteins should help to understand processes critical to resistance to beech bark disease and to develop biomarkers for use in tree breeding programs and for the selection of resistant trees prior to or in early stages of BBD development in stands. Early identification of resistant trees (prior to the full disease development in an area) will allow forest management through the removal of susceptible trees and their root-sprouts prior to the onset of disease, allowing management and mitigation of costs, economic impact, and impacts on ecological systems and services.

Relationships among beech bark disease, climate, radial growth response and mortality of American beech in northern Maine, USA

SummaryA majority of beech forests across Maine first experienced beech bark disease (BBD) from 1935 to 1960 when sap feeding by an introduced beech scale insect, Cryptococcus fagisuga, allowed lethal fungal infections primarily by Neonectria ditissima and/or Neonectria faginata. Beech stands along the Maine–Quebec border in northern Maine were excluded from this initial killing phase presumably due to cold winter temperatures that inhibited scale survival. However, a sharp increase in beech mortality after 2002 occurred in previously uninfected border stands and stands long affected by BBD. Beech mortality averaged 50% across northern Maine during 2003–2006. To identify plausible stresses that could explain the mortality, a dendropathological study was conducted from 2005 to 2006 in northern Maine that quantified temporal and spatial relationships between possible stressors with beech mortality and growth decline. Nineteen sets of high‐ and low‐mortality plots were located randomly across four bioregions. Increment cores were taken from both beech trees (n = 565) and associated tree species (n = 450). A growth change index of increments was used to evaluate beech responses to biotic and climatic stresses. A prolonged period of relatively mild winters without temperatures lethal to scale insect (<−34°C) from 2000 to 2004 coupled with low August–October precipitation from 2000 to 2003 may have provided ideal conditions initiating a widespread scale epidemic. A major drought period from 1999 to 2002 coincided with growth decline and a significant increase in beech mortality across all regions included in this study. Neonectria was found infecting weakened trees across the region. Drought, beech scale and Neonectria are plausible explanations for the episode of high beech mortality in northern Maine. This is the first report of a major killing phase of beech within the BBD ‘aftermath’ forests.

An episodic model of honeydew production in scale insects

AbstractHoneydew produced by sooty beech scale insects (Ultracoelostoma spp., Homoptera: Coelostomidiidae) is a keystone ecological process in New Zealand beech (Nothofagus spp., Nothofagaceae) forest. This work puts forward a model of honeydew production based on individual insects that presumes feeding and excretion are episodic processes driven by the insect rather than the passive processes that were previously assumed. The model is parameterized using existing data and then compared to an independent pre‐existing dataset. The model suggests that over a 12‐h period, on average the insects suck sap for 2 h, and excrete waste sap for 12 min. Resource uptake by the insects appears to be limited by the time required to process the sap, consistent with the observed relationship between honeydew production rates and ambient temperature. This implies that insect feeding rates may be ultimately limited by the low nitrogen content of phloem sap.

Annual Meeting, Winnipeg, Manitoba, 2009

Annual Meeting, Winnipeg, Manitoba, 2009

Evaluation of Resistance to the Beech Scale Insect (Cryptococcus fagisuga) and Propagation of American Beech (Fagus grandifolia) by Grafting

Abstract Scions collected from diseased trees and from those without symptoms of beech bark disease (BBD) were cleft-grafted in 2003 and 2004 onto rootstock of unknown resistance to BBD. Grafting success varied among genotypes and year (30% in 2003 and 12% in 2004), and improved with increasing rootstock diameter. Successful grafts were used to test resistance to the beech scale insect, Cryptococcus fagisuga (the initiating agent of BBD) by introducing eggs onto the bark of scions and allowing time for the emergence of all developmental stages of the insects. Significantly fewer insects colonized scions collected from putatively resistant trees than those collected from diseased trees. In some cases, where egg placement overlapped a portion of the rootstock, insect colonies developed on the rootstock but not on the scion collected from resistant trees. Occasionally, scions from putatively resistant trees were colonized, whereas some of those from diseased trees were not. When scions from putatively resistant trees were heavily colonized, only adult insects were present and no eggs or other life stages of the insect were found. The findings indicate that the extent of resistance to the scale insect (hence to BBD) ranges from partial to total resistance.

A dynamical model of honeydew droplet production by sooty-beech scale insects ( Ultracoelostoma spp.) in New Zealand Nothofagus forest

Sugar-rich honeydew production by phloem-feeding sooty beech scale insects ( Ultracoelostoma spp.) is a keystone ecological process in New Zealand beech ( Nothofagus) forest. A dynamical model to describe the formation of individual honeydew droplets is derived using simple fluid dynamics. The model assumes that the insects play little part in regulating flow, and that flow is driven by phloem hydrostatic pressure and regulated by environmental conditions affecting water evaporation from droplets. The model predicts different types of behaviour depending on local environmental conditions. In dry conditions, evaporation rates are high and honeydew droplets can become so concentrated that further excretion is prevented and droplet formation ceases. In humid conditions, the high concentrations required to prevent droplet formation do not occur and droplets continue to grow indefinitely. The model is fitted to new data and the data are used to estimate values for the rate of flow of phloem sap through the insect and for the concentration required to prevent further excretion. Model predictions provide a close qualitative match to field data. However, rates of fluid flow from the trees through the insects would need to be much greater than the model assumes to produce values for droplet production that match field data. This suggests that the insects are playing an active role in regulating the flow rate.

Spread of beech bark disease in the eastern United States and its relationship to regional forest composition

Beech bark disease (BBD) is an insect–fungus complex involving the beech scale insect ( Cryptococcus fagisuga Lind.) and one of two canker fungi. Beech scale was introduced to Halifax, Nova Scotia around 1890, presumably with the fungus Neonectria coccinea var. faginata Lohm. The disease has subsequently spread through a large portion of the range of beech. We used historical maps of the extent of the advancing BBD front (defined by presence of scale insects) in North America to estimate its rate of spread as 14.7 ± 0.9 km/year. This estimate did not account for stochastic “jumps” by the scale insects to several disjunct locations; therefore, this rate is a conservative estimate. Comparison of the year of scale colonization with beech density did not suggest a relationship between the scale spread rate and beech density. Our analyses also indicated that BBD has invaded less than 30% of regions where beech is present, but it has invaded most of the regions where beech is a dominant component of stands. Despite regional increases in beech mortality following invasion, considerable amounts of live beech remain in invaded areas. Moreover, the volume of beech has increased in most areas, though generally at lower rates than that observed for associated tree species.

Establishment success of sooty beech scale insects, Ultracoelostoma sp., on different host tree species in New Zealand

The sooty beech scale insect (Ultracoelostoma sp.) (Hemiptera: Margarodidae) exhibits a highly patchy distribution at local and regional scales. A major factor driving this common distributional phenomenon in other phloem-feeding insects is aggregation and local adaptation. The aim of this study was to determine if Ultracoelostoma was locally adapted to its natal host trees, by contrasting the establishment rates of first instar “crawlers” in reciprocal transfers to natal versus novel hosts. Although there are two closely-related species of sooty beech scale insect, the morphological characters of crawlers in this study were intermediate between those of U. assimile and U. brittini. However, all of the voucher specimens examined had consistent morphology, indicating that they belong to one species which we refer to as Ultracoelostoma sp. Reciprocal transfers of crawlers were carried out between individual red beech (Nothofagus fusca), as well as between mountain beech (N. solandri) and red beech trees, to ascertain if insects had become locally adapted to their individual host tree or to host species. In total, 480 crawlers were placed in enclosures on their natal and novel host trees, of which only 32 (6.7 %) became established. No evidence for local adaptation, either to individual host trees or to host tree species, was found. There was also no difference in crawler establishment between natal and novel hosts. However, crawlers originating from mountain beech trees had significantly higher establishment rates on both natal mountain beech and novel red beech hosts, than did crawlers originating from red beech trees. The superior ability of mountain beech crawlers to become established, even on novel red beech trees, suggests that scale insects on mountain beech trees have higher individual fitness (possibly due to maternal effects mediated by differences in host nutritional quality, defensive compounds or growth rate). This increased fitness may result in crawlers being better provisioned to search for appropriate establishment sites. The results of this study indicate that beech scale insects perform better on mountain beech at this site, although crawlers did not preferentially establish on mountain beech.

Tree Cavity Resources for Dependent Cavity-Using Wildlife in West Virginia Forests

Abstract We assessed and compared tree cavity resources for dependent wildlife among various forest cover types of West Virginia. The study was conducted in the Greenbrier and Potomac Ranger Districts of the Monongahela National Forest (MNF). From the fall of 1999 through the spring of 2001, 25 50-m radius study plots were established in each of a Society of American Foresters (SAF) central hardwood, northern hardwood, and subalpine forest cover type. Cavity tree abundance significantly differed among the three forest cover types (P < 0.0001), with the highest cavity tree abundance in the central hardwood type (x¯ = 16.4; SE = 5.3), followed by the northern hardwood type (x¯ = 12.7; SE = 6.8), and lastly the subalpine type (x¯ = 7.2; SE = 3.6). Relative cavity likelihood was highest for black locust (Robinia pseudoacacia), followed by American beech (Fagus grandifolia), sugar maple (Acer saccharum), and chestnut oak (Quercus prinus). American beech cavity numbers currently may be influenced by increased mortality from recent outbreaks of beech bark disease, initiated by the beech scale insect (Cryptococcus fagisuga). Management of red spruce (Picea rubens) forests should consider numbers of nearby large hardwoods to provide cavity resources for dependent wildlife.

Vertical stratification in the spatial distribution of the beech scale insect (Ultracoelostoma assimile) inNothofagustree canopies in New Zealand

Abstract. 1. The degree of infestation by New Zealand sooty beech scale insects (Ultracoelostoma assimile, Homoptera: Margarodidae) varies dramatically among adjacent southern beech trees (Nothofagusspp., Fagaceae), but has previously been assumed to be uniformly or randomly distributed within individual host trees. In this study, a full‐census survey was conducted from ground level to canopy level on 14 naturally occurring, canopy‐dominant red beech (Nothofagus fusca) trees (size range 38.7–107.6 cm diameter at breast height) to determine the degree of within‐tree heterogeneity in herbivore density.2. The within‐tree distribution of the sooty beech scale was vertically stratified and highly heterogeneous, with the greatest densities occurring on bark surfaces in the canopy rather than on the trunk, and on the lower rather than upper sides of the branches. The spatial distribution was strongly negatively correlated with trunk and branch diameter, and increasing bark thickness (as a function of diameter) provides a plausible explanation for differences in the establishment and population density of sooty beech scale insects with trunk and branch size. Furthermore, there was a significant change in the spatial distribution of scale insect populations on trunks and branches of trees of increasing diameter at breast height. This indicates a strong temporal component to the spatial dynamics of the sooty beech scale insect driven by changing host phenology. Future studies on phytophagous insects infesting large host trees need to consider more explicitly changes in population dynamics through space and time.3. Because of the high degree of within‐tree heterogeneity in population density, the total population size of scale insects on an individual tree could not be predicted from any measure of population density low on the trunk. However, the dry weight biomass of sooty mould fungi growing on the ground beneath infested trees was a remarkably accurate predictor of the total population size of scale insects. The use of sooty mould fungi as a relative measure of population size could be incorporated into studies of other honeydew‐producing hemipterans, since the growth of sooty mould is a distinctive feature synonymous with high concentrations of honeydew production worldwide.

Density‐dependent effects on the reproductive fitness of the New Zealand beech scale insect (Ultracoelostoma assimile) across multiple spatial scales

Abstract. 1. Intraspecific competition can be an important factor influencing the individual fitness of organisms. This study reports density‐dependent effects on the fecundity of the beech scale insect (Ultracoelostoma assimile, Hemiptera: Margarodidae) on naturally occurring, canopy‐dominant red beech (Nothofagus fusca, Fagaceae) trees in New Zealand. For the first time an increasing intensity of intraspecific competition at increasing spatial scales within individual host trees is demonstrated.2. Beech scale insect ‘tests’ containing adult female scale insects and eggs were collected from the trunks of 10 red beech trees [17.7–48.5 cm in diameter at breast height (1.4 m), d.b.h.] with varying densities of scale insect infestation. The relationship between individual female fecundity and scale insect density at three spatial scales: local (within 5 cm), lower trunk (below 2 m above ground level), and whole tree, was tested.3. Beech scale insect fecundity was density dependent, with total female egg load decreasing with increasing scale insect density. The strength of the density‐dependent effect increased with increasing spatial scale, suggesting that scale insects are creating a tree‐wide drain on the quality of phloem sap, rather than depleting nutrients from localised, high‐density areas within trees. These results indicate that at high densities, the New Zealand beech scale insect can have a negative effect on the nutritional quality of the phloem of red beech, thus negatively affecting conspecifics elsewhere on individual host trees. The increasing intensity of the effect with increasing spatial scale within individual trees emphasises the importance of measuring density‐dependent effects at the appropriate spatial scale.

The effect of introduced wasp (Vespula vulgaris, Hymenoptera: Vespidae) predation on the dispersive life history stages of beech scale insects (Ultracoelostoma spp., Homoptera: Margarodidae)

Introduced wasps reach huge densities in honeydew beech forests and have been found to substantially reduce the abundance of many species of invertebrates. However, the effects of wasps on the beech scale insect, which has been identified as a key species due to the large amounts of carbohydrate-rich honeydew it produces, have not been investigated. The aim of this study was to determine the effect of direct wasp predation on winged, adult male scale insects, whose flight period coincides with the peak wasp season. We found that wasps have no discernible effect on the persistence of male scale insects. Samples from malaise flight intercept traps inside and outside a wasp controlled area also showed that high densities of wasps had no effect on the activity-density of male scale insects or first instar crawlers. The peak in the male scale insect flight period was in mid February, two months later than the peak observed in a previous study of male beech scale insects, although the biotic or abiotic factors driving this variation are still unknown. The significance of these results is hard to quantify without some knowledge of the role that male scale insects play in the population dynamics of the beech scale insect, but it appears that introduced wasps do not significantly affect the life history or population density of beech scale insects.

Black Bear Foraging in Response to Beech Bark Disease in Northern Vermont

Several studies have demonstrated the relationship between black bear (Ursus americanus) reproductive success and the availability of hard mast. Beech bark disease (BBD) has been shown to reduce mast production in beech trees; however, no studies have investigated the relationship between bear foraging preferences of beech trees and the presence of BBD. To investigate this, we measured the severity of Nectria fungus and beech scale insect on freshly clawed and unclawed trees in pooled beech stands in northern Vermont. Our results suggest that bears do not have a strong preference for climbing healthier beech trees in aftermath forests. Changes in landscape composition and in cultural values appear to have been more important processes affecting black bear populations today than has BBD; however, we still advocate management strategies to minimize the impacts of this disease.

Beech bark disease in northern hardwood forests: the importance of nitrogen dynamics and forest history for disease severity

Beech bark disease has been a major cause of mortality of American beech (Fagus grandifolia Ehrh.) in North America during the past century. Previous studies have suggested a positive relationship between disease severity and both bark nitrogen content and tree size, presumably due to higher rates of infestation by beech scale insects, which allow more extensive infection of the tree by Nectria fungi. Recent concerns about nitrogen saturation in northeastern forests, particularly in old-growth forests, led us to examine patterns of disease severity as a function of bark tissue nitrogen content in old-growth and second-growth forests in the Adirondack region of New York and northern Maine. Trees growing in old-growth stands possessed significantly higher levels of bark nitrogen than similarly sized trees in second-growth forests. The severity of disease symptoms was more acute in the old-growth forests and was positively correlated with the percent nitrogen of the bark in both forest types. Comparisons of the coefficients of variation between beech bark sampled from disease-free forests in the upper peninsula of Michigan and that sampled from diseased forests indicated that elevated bark nitrogen concentrations in diseased trees were a cause and not an effect of disease presence. While there was no difference in disease severity between control and nitrogen-fertilized forests in Maine, these forests had both been exposed to the disease for longer time periods than the other studied forests and they are likely approaching nitrogen saturation.

Competition for honeydew between two social wasps in South Island beech forests, New Zealand

Honeydew is a sugary secretion of beech scale insects (Ultracoelostoma spp.). Two introduced species of wasps forage on the sugar droplets in New Zealand beech forests. We hypothesize that competition between them may explain whyVespula germanica has become locally extinct in beech (Nothofagus) forest invaded byV. vulgaris. Changes in behaviour of the two wasp species in response to changes in the honeydew resource were monitored. Foraging and rainfall separately and together reduced the honeydew standing crop. In response to the standing crop decreasing, more wasps were found on honeydew trees, they became less active, spent more time lapping the tree surface, and ingested drops of honeydew at a slower rate.V. vulgaris was more active, and obtained drops and energy at a higher rate thanV. germanica. These behavioural differences may lead to competitive advantages affecting queen size and possibly survival.