A geographically variable model of hemlock woolly adelgid spread

The hemlock woolly adelgid (HWA) (Adelges tsugae) has spread through the range of eastern hemlock (Tsuga canadensis) leaving dead hemlock trees in its wake. We combined county and previously unavailable township level infestation records with geographic variables including plant hardiness zone, elevation, forest cover type, urbanization, precipitation, temperature, and hemlock range in a geographic information system to build models linking HWA spread to the structure and characteristics of the environment. We explored the connections between site variables and spread rate using quantile regression, Tobit regression, a parametric model for heterogeneous error variance, and classification and regression tree modeling. The results show that since 1990 HWA has spread at a rate closer to 12.5 km/yr rather than the 20–30 km/yr previously estimated, however spread rates vary significantly with environmental variables. County-based data show a faster rate of range expansion in the south, 15.6 km/yr, and very slow spread in the northern part of the current range of HWA. The rate of spread based on township records for Pennsylvania and north is 8.13 km/yr. Our study suggests that HWA spreads more slowly in colder areas, with a mean minimum temperature of  − 26.1°C (plant hardiness zone 5B) delineating areas of slower range expansion. HWA also spreads more slowly during cold years, those with lower than average mean January temperatures. Our analysis demonstrates the value of quantile regression, Tobit regression, and classification and regression tree models for understanding the spread of invasive, exotic insects.     

Using dendrochronology to model hemlock woolly adelgid effects on eastern hemlock growth and vulnerability

This study examined the relationship between eastern hemlock (Tsuga canadensis (L.) Carr.) crown condition and changes in radial growth associated with infestation by hemlock woolly adelgid Adelges tsugae (Homoptera: Adelgidae) (HWA). Tree-ring chronologies of eastern hemlock were used to develop a binomial decline index based on three consecutive years of below average growth. Radial growth decline was modeled, using logistic regression, as a function of an extensive array of tree, crown, and site variables that were collected over an 11 year period in Delaware Water Gap National Recreation Area. Some site-related variables such as site-location and aspect were significantly related to decline probabilities when considered individually. However, the total proportion of response variance accounted for was low, and the only site variable included in the final model was mean plot-level HWA infestation level. For every 1% increase in mean percent HWA infestation per plot, there was an 8% increase in the likelihood that a tree would be classified as being in decline. Tree crown variables such as live crown ratio, crown density, and the modified ZB_adj index, a combination of foliage transparency and branch dieback, had the most explanatory power, both individually and in the final model. These crown variables were relatively accurate predictors of the degree of hemlock growth decline during HWA infestation.     

Using Satellite Images to Classify and Analyze the Health of Hemlock Forests Infested by the Hemlock Woolly Adelgid

A method is described to classify stands of eastern hemlock by health condition, at the landscape level, using remote sensing. The hemlock woolly adelgid has been a major cause of hemlock decline in Connecticut since 1985, resulting in varying degrees of defoliation in the region. A 1985 Landsat Thematic Mapper (TM) image was classified to develop a base line of once healthy hemlock stands. Radiance normalization and non-hemlock masking techniques were used to pre-process a 1995 TM image. Several techniques were used to transform the 1995 TM image; each was followed by cluster analysis to separate hemlocks into four levels of tree vigor. We evaluated 600 trees at 150 sites across the study area using the USFS Crown Condition Rating Guide. These field data were used to measure the accuracy of various health classification techniques. The Modified Soil Adjusted Vegetation Index-2 (MSAVI₂) transform provided the best overall accuracy, 82.1%, for classifying hemlock according to tree vigor. Non-parametric statistics were used to determine if there were any significant variations in distribution of hemlock pixels by health class in association with features in the landscape. Several features were found to be statistically significant at a confidence level of 0.001. These were aspect of slope, hydrology group (infiltration rate), depth to bedrock, soil order, drainage class (hydraulic conductivity), and surface texture.     

Spectral response and spatial pattern of Fraser fir mortality and regeneration,Great Smoky Mountains,USA

High elevation Fraser fir (Abies fraseri) forests of the Southern Appalachians have undergone widespread mortality since the introduction of the balsam woolly adelgid in the 1950s. Resulting changes in ecosystem pattern and process (e.g., stand dynamic processes) have greatly affected floral and faunal communities. In this project, we integrated field observations, geographic information system topographic models, and 1988–1998 satellite imagery to analyze spatial and temporal conditions of Fraser fir and spruce-fir ecosystems in Great Smoky Mountains National Park. Tasseled cap indices (brightness, greenness, and wetness) and associated spectral changes for Landsat TM digital data were statistically modeled by topographic variables. Spectral changes were recorded using change vector analysis (CVA) and spherical geometry at multiple scales: individual sites, local ridges, and across the east-west gradient of the study area. Significant relationships were found between elevation and observed spectral changes and among mountain sites representing the east-west chronosequence of adelgid infestation. Topographic derivatives were related to tasseled cap and CVA measures in summary statistics, regression, and correlation analysis, revealing significantly different mortality and regeneration pathways that were a function of topographic settings. Geographic variations of these vectors also detail the scope of east-west and localized upslope progression of fir mortality. The application of CVA provided the ability to summarize variation in spectral changes (magnitude and direction) and to ascribe measures to mortality and regeneration processes.     

Biology and development of <Emphasis Type="Italic">Laricobius kangdingensis</Emphasis> Zilahi-Balogh and Jelínek,a newly discovered predator of <Emphasis Type="Italic">Adelges tsugae</Emphasis>

The biology and temperature-dependent development of Laricobius kangdingensis Zilahi-Balogh and Jelínek (Coleoptera: Derodontidae), a newly described predator of hemlock woolly adelgid (HWA), Adelges tsugae Annand (Hemiptera: Adelgidae) were investigated and compared with a related HWA predator, L. nigrinus Fender, that has already been released. As with other Laricobius species, there are four larval instars. The female to male sex ratio was 1:1.1. Mean lifetime fecundity per female was 196.4 eggs and 97.9 eggs for the parental generation (P₁) and first filial generation (F₁), respectively. Developmental rates at 6, 9, 12, 15, and 18°C were studied between fall 2002 and spring 2004 and used to determine low temperature development thresholds for the egg (2.8°C), and larval (1.6°C) stages. The egg and larval thresholds are lower than those observed for L. nigrinus. Laricobius kangdingensis individuals completed development only at 12 and 15°C; however, the adults did not emerge from aestivation after pupation. Our results suggest that L. kangdingensis may be a promising addition to the complex of predators currently being reared for control of HWA. Laricobius kangdingensis is long-lived, exhibits high fecundity, and can complete development on North American HWA. However, further studies will be necessary to secure its clearance for release, and the source of high mortality in the laboratory must be identified in order to improve its survival for mass-rearing. Handling editor: Eric Lucas     

Hemlock Woolly Adelgid in New England Forests: Canopy Impacts Transforming Ecosystem Processes and Landscapes

Exotic insect pests may strongly disrupt forest ecosystems and trigger major shifts in nutrient cycling, structure, and composition. We examined the relationship between these diverse effects for the hemlock woolly adelgid (HWA, Adelges tsugae Annand) in New England forests by studying its impacts on local canopy processes in stands differing in infestation levels and linking these impacts to shifts in canopy nutrient cycling and stand and landscape effects. HWA initiated major changes in canopy biomass and distribution. Whereas uninfested trees exhibit a significant decline in canopy biomass from the center to the periphery and a positive correlation between total needle litter and estimated biomass, infested trees have significantly less total canopy biomass, produce less new foliage, shed relatively more needles, and exhibit no correlation between litter and canopy biomass. Foliar N content of infested trees was 20%–40% higher than reference trees, with the strongest increase in young foliage supporting the highest densities of HWA. Foliar %C was unaffected by HWA or foliar age. Epiphytic microorganisms on hemlock needles exhibited little variation in abundance within canopies, but colony-forming units of bacteria, yeast, and filamentous fungi were 2–3 orders of magnitude more abundant on medium and heavily infested than uninfested trees. Throughfall chemistry, quantity, and spatial pattern were strongly altered by HWA. Throughfall exhibits a strong gradient beneath uninfested trees, decreasing in volumes from the canopy periphery to the trunk by more than 45%. The amount of throughfall beneath infested trees exhibits no spatial pattern, reaches 80%–90% of the bulk precipitation, and is characterized by significantly higher concentrations of nitrogen compounds, dissolved organic carbon, and cations. Across the southern New England landscape there is a strong south-to-north gradient of decreasing hemlock tree and sapling mortality and understory compositional change that corresponds to the duration of infestation. Regionally, black birch (Betula lenta L.) is profiting most from hemlock decline by significantly increasing in density and cover. These findings suggest that it is necessary to study the connections between fast/small-scale processes such as changes in nutrient cycling in tree canopies and slow/integrative processes like shifts in biogeochemieal cycling and compositional changes at forest stands and landscapes to better understand the effects of an exotic pest species like HWA on forest ecosystem structure and function.     

A Technique to Identify Changes in Hemlock Forest Health over Space and Time Using Satellite Image Data

The objective of this study was to develop a technique to classify health of eastern hemlock stands using historical satellite images. While remote sensing and geographic information systems have been used successfully to classify forest health using recent images, applying this process to older images is problematic because contemporaneous field data are not available to measure the accuracy of the classification of historical images. Data ranges were established for each hemlock health class using a contemporary image and field data. These ranges were used to level-slice archived images to create a series of health-class maps that show changes in forest health over time. By applying cross-tabulation procedures to pairs of classified images, it is possible to construct a transition map that indicates how the hemlock health class of each pixel in the images of the study area has changed over time. The resulting maps provide a look back at forest conditions of the past and can be used to identify areas of special interest.     

Hemlock Declines Rapidly with Hemlock Woolly Adelgid Infestation: Impacts on the Carbon Cycle of Southern Appalachian Forests

The recent infestation of southern Appalachian eastern hemlock stands by hemlock woolly adelgid (HWA) is expected to have dramatic and lasting effects on forest structure and function. We studied the short-term changes to the carbon cycle in a mixed stand of hemlock and hardwoods, where hemlock was declining due to either girdling or HWA infestation. We expected that hemlock would decline more rapidly from girdling than from HWA infestation. Unexpectedly, in response to both girdling and HWA infestation, hemlock basal area increment (BAI) reduced substantially compared to reference hardwoods in 3 years. This decline was concurrent with moderate increases in the BAI of co-occurring hardwoods. Although the girdling treatment resulted in an initial pulse of hemlock needle inputs, cumulative litter inputs and O horizon mass did not differ between treatments over the study period. Following girdling and HWA infestation, very fine root biomass declined by 20–40% in 2 years, which suggests hemlock root mortality in the girdling treatment, and a reduction in hemlock root production in the HWA treatment. Soil CO₂ efflux (E _soil) declined by approximately 20% in 1 year after both girdling and HWA infestation, even after accounting for the intra-annual variability of soil temperature and moisture. The reduction in E _soil and the concurrent declines in BAI and standing very fine root biomass suggest rapid declines in hemlock productivity from HWA infestation. The accelerated inputs of detritus resulting from hemlock mortality are likely to influence carbon and nutrient fluxes, and dictate future patterns of species regeneration in these forest ecosystems. AEN performed research and analyzed data; NW performed research, analyzed data, and wrote the article; CRF contributed new methods, analyzed data, and wrote the article; RLH designed the study; JMV conceived of and designed the study; and BDK performed research.     

Biological invasion as a natural experiment of the evolutionary processes: introduction of the special feature

Although biological invasion has a devastating impact on biodiversity, it also provides a valuable opportunity for natural experiments on evolutionary responses. Alien populations are often subject to strong natural selection when they are exposed to new abiotic and biotic conditions. Native populations can also undergo strong selection when interacting with introduced enemies and competitors. This special feature aims to highlight how evolutionary studies take advantage of biological invasion and, at the same time, emphasizes how studying evolutionary processes deepens our understanding of biological invasions. We hope this special feature stimulates more invasion studies taking evolutionary processes into account. Those studies should provide fundamental information essential for formulating effective measures in conserving native biodiversity, as well as valuable empirical tests for evolutionary theories.     

Development and feeding of <Emphasis Type="Italic">Tetraphleps galchanoides</Emphasis>, a predator of the hemlock woolly adelgid

Tetraphleps galchanoides Ghauri (Hemiptera: Anthocoridae) nymphs were collected from hemlock woolly adelgid (HWA) Adelges tsugae Annand (Hemiptera: Adelgidae) infested Tsuga sp. in Baoxing, Sichuan, China. First and second stage nymphs collected from foliage shipped from China; were reared to adults and tested for feeding rates and host preferences. They were reared at 5, 8, 12, and 15 ± 1 °C from November to December, January to March, April, and May to June, respectively, in the quarantine laboratory at Virginia Polytechnic Institute and State University. At 8 °C, development time was 15, 20, and 40 days for the N-III, IV, and V nymphal stages, respectively. Adult males lived 83 days with a range of 21–147 days. A single adult female lived for 21 days. At 5 °C, second stage T. galchanoides nymphs consumed 0.8 HWA nymphs per day, and 2.0 HWA nymphs per day at the N-V stage. At 8 °C, consumption of HWA nymphs ranged from 1.3 to 3.4 nymphs per day for the N-III to N-V stages, respectively. Adult T. galchanoides consumed more HWA eggs than HWA adults, pine bark adelgid (PBA) Pineus strobi (Hartig) (Hemiptera: Adelgidae) adults, and eggs in no-choice tests. In choice tests with HWA eggs and PBA eggs, more HWA eggs were eaten. Adult and nymph body measurements are presented for determination of nymphal instars.     

Development and reproductive biology of Laricobius nigrinus, a potential biological control agent of Adelges tsugae

Biological studies on Laricobius nigrinus Fender (Coleoptera: Derodontidae) were conducted in the laboratory to obtain basic information on this littleknown predator. Laricobius nigrinus is acandidate biological control agent of thehemlock woolly adelgid, Adelges tsugaeAnnand (Homoptera: Adelgidae), an exotic peston eastern (Tsuga canadensis (L.)Carrière) and Carolina (T.caroliniana Engelmann) hemlocks in the easternUnited States. It is univoltine andundergoes an aestival diapause. Post-aestivation activity period was 36.6 and30.8 weeks for males and females, respectively. Adult activity and oviposition are wellsynchronized with the over-wintering generationof A. tsugae. Mean lifetime fecunditywas 100.8 eggs over a mean duration of 13.2weeks oviposition period. Within thetemperature range (12–18°C) studied,development was fastest at 18°C. Meandevelopment time from egg to adult was 88.8,64.8 and 46.6 days at 12, 15 and 18°C,respectively. Laricobius nigrinus hasfour larval instars. Mean larval consumptionwas 225.9 and 252.3 A. tsugae eggs at 12and 18°C, respectively. Thesefindings provide essential data on the rate ofdevelopment and feeding capacity of L. nigrinusat temperatures typical of ambientconditions during late winter/early spring inVirginia. Its rapid development at18°C indicates that it has potential asa biological control agent of A. tsugaebecause of its synchrony with the developmentof the over-wintering generation of A. tsugaein eastern United States.     

Fermentation media and production of exotoxin by three varieties of Bacillus thuringiensis

The insecticidal activities of the exotoxin produced by three varieties of Bacillus thuringiensis grown in six fermentation media were determined by testing the supernatants against larvae of the house fly, Musca domestica, and the black cutworm, Agrotis ipsilon. The activities of the exotoxins from the isolates varied when they were grown in the same medium and also when they were grown in different media. When an isolate of B. thuringiensis var. thuringiensis, and of var. tolworthi were grown in proflo broth, the supernatants produced were more toxic to house fly than to black cutworm larvae, indicating the presence of more than one exotoxin. Autoclaving the supernatants for 15 and 30 min further demonstrated the presence of several exotoxins.     

FISH荧光原位杂交技术在污水生物脱氮研究中的应用

简要介绍了荧光原位杂交（FISH）的基本原理,着重讨论近年来该技术在污水生物脱氮研究中的应用现状和特点。研究表明：FISH技术能够准确地表现污水处理反应器中脱氮菌群落的类型和结构形态。但在关于SRT、DO、C／N比等工艺参数的变化对脱氮反应器中微生物类型、数量和结构的影响等方面的研究还有待深入。FISH技术与PCR—DGGE和16SrRNA／rDNA序列分析等技术相结合是对污水处理构筑物中生物脱氮群落深入研究的发展方向。