Thursday, May 27
All times are listed in Central Daylight Saving time.
8:30 a.m. – Plenary Session 2
The Macroecology of Historical Insect Invasions
Sandy Liebhold, USDA Forest Service
Beyond Buzz—How to Harness the New Media Environment to Conserve the Actual Environment
Andrew Revkin, Columbia University
9:30 – Break
10:00 – Concurrent Sessions 2
Moderators: Chris Asaro, John Nowak, Chris Fettig
Speakers: Chris Asaro, John Nowak, Chris Fettig, Matt Ayers, Matt Ayers, Kamal Gandhi, Kathy Bleiker, Jason Moan
The rapid pace of environmental and socioeconomic change poses considerable challenges to forest managers throughout North America. The goal of this 2-hr workshop is to explore relevant issues to the management of bark beetles within the broader social, political and biophysical environment. Changes in the frequency and severity of other disturbance regimes and stressors, forest ownership and land use patterns, and market forces will be discussed for each of five regions. Speakers will address how these factors influence management considerations today, and more importantly how anticipated changes will likely influence management considerations and bark beetle impacts in the future.
- Managing bark beetles during a period of rapid environmental and socioeconomic change: A brief introduction: Chris Asaro, John Nowak, Chris Fettig
- Northeastern US: Matt Ayers
- Southeastern US: Kamal Gandhi
- Bark beetles are eating the West: Changing environmental and socioeconomic influences: Chris Fettig
- Western Canada: Kathy Bleiker
- Alaska: Jason Moan
Moderators: Rob Venette, Andrew Graves
Speakers: Andrew Graves, Rob Venette, Brian Aukema, Andrea Hefty, Jorge Macias Samano
The concomitant movement of wood and insects within (and across) national borders creates opportunities for the introduction of invasive pests. A common misconception is that invasive pests must come from overseas. This session begins with select cases that illustrate the severe impacts that can occur when forest pests are moved to naïve ecosystems that are still within national borders. We apply a simple framework to assess how risks associated with these species might differ within a country. Lastly, we discuss potential management options that would not necessarily require federal regulatory but could mitigate these risks.
- Welcome: Andrew Graves, Rob Venette
- Heading west: Ips grandicolis is on the move: Brian Aukema
- Goldspotted oak borer and walnut twig beetle, domestic invasive species from the western US: Andrea Hefty
- Forest insects from Mexico and Central America: Cause for concern?: Jorge Macias Samano
- Simplified risk assessments for domestic invasive species: Rob Venette
- Management options for domestic invasive species: Andrew Graves
Moderator: Mike Howe
Outbreaks and range dynamics of baldcypress leafroller in the southeastern US
Samuel F. Ward, Kristy M. McAndrew
Several recent outbreaks of native forest insects have been unprecedented in their extent and/or severity. The first recorded outbreak of baldcypress leafroller (Archips goyerana Kruse; Lepidoptera: Tortricidae), a native defoliator of baldcypress, began in Louisiana in 1983. For years following the onset of the outbreak the causal agent was believed to be a congener, fruittree leafroller (A. argyrospila Walker), as baldcypress leafroller was not formally described until 2000. The outbreak is still ongoing, surpassing 100,000 hectares of defoliation in 2017 alone, but has remained confined to southern Louisiana. However, baldcypress leafroller has been reported from Mississippi and the range of baldcypress extends across the southeastern US and reaches southern portions of the midwestern and northeastern US. The range limits of endemic populations of baldcypress leafroller and factors inhibiting such populations from reaching epidemic levels remain unknown. A quantitative analysis of the initiation, persistence, and spread of defoliation in Louisiana will be presented along with a summary of (i) previously reported evidence for drivers of the outbreak and (ii) ongoing efforts to quantify the range dynamics of epidemic and endemic populations.
It’s a dry heat: How trees reprioritize carbon in a hotter, drier world and the potential impacts for bark beetle ecology
Heat and drought affect plant chemical defenses and thereby plant susceptibility to pests and pathogens. Yet, our understanding of the impacts of heat and drought on defense is primarily based on data from potted seedlings, making it unclear how older age classes respond to stress. Furthermore, the carbon pools that support secondary metabolism under predicted drought stress are largely assumed. We measured needle and woody tissue secondary metabolites and primary physiology from mature Pinus edulis during a unique temperature and drought manipulation field experiment. While heat had no effect on total monoterpene concentrations, trees under combined heat and drought exhibited ~85% and 35% increases in needle and woody tissue, respectively, over multiple years. Physiological variables explained less than 10% of the variation in total monoterpenes for both tissue types while starch and glucose + fructose measured one-month prior explained ~25% of woody tissue total monoterpene concentrations. Notably, some key monoterpene compounds with known roles in bark beetle ecology decreased. These shifts may make trees more favorable for bark beetle attack rather than well-defended, which one might conclude if only considering total monoterpene concentrations. Our results point to cumulative effects of heat and drought that reprioritize specific carbon pools toward defense.
The importance of energy-water limitation threshold in drought impact studies
Forest diebacks have increased in magnitude in many regions in response to greater water limitation. “Hotter droughts” are predicted to increase under climate change and result in significant restructuring of forest composition and ecosystems services. Many drought-related studies, however, focus on water limited systems, where water—not energy—poses the greatest constraint on photosynthesis. Contrary to expectation, hotter, drier conditions in energy limited systems may cause greater growth, as the growing season is extended. Thus, identifying the location of the energy-water limitation threshold is critical to predict forest mortality under climate change. Here we assess the impacts of the recent extreme drought in California (~2012-2015) on whitebark pine across the central and southern Sierra Nevada. We use a combination of over 700 tree-rings and over 1,000 stable isotope samples to test whether extreme drought led to greater growth or greater physiological stress. We show that during extreme drought, the energy-water limitation threshold shifted upslope into higher elevation forests. Trees growing near this threshold experienced some physiological stress, but trees far from this threshold experienced positive growth. These results suggest that extreme drought has a more nuanced effect on average productivity for forests that occur across strong climatic gradients.
Suitability of current and future climates in Canada and the United States for the potential establishment of the European spruce bark beetle, Ips typographus
Kishan Sambaraju, Chantal Côté
Non-native pest introductions pose a serious threat to forest health worldwide. In North America, exotic bark beetles are commonly intercepted at the ports of entry, and among the species reportedly encountered, the European spruce bark beetle (Ips typographus L.) is one of the most frequent. Native to Eurasia, this species causes serious damage to Norway spruce (Picea abies (L.) H. Karst.) in its indigenous range; however, I. typographus also has the capacity to survive and reproduce on important North American spruce species. Climate plays a critical role in regulating multiple aspects of I. typographus life history such as voltinism, flight behavior, and population density. We used species distribution models (SDMs) to assess whether climates in Canada and the United States are suitable for the potential establishment of I. typographus. We also wanted to assess future geographic shifts in climatic suitability in this region under climate change. Species distribution models are modeling algorithms that associate species occurrences with predictors such as climate variables and can be used to characterize habitat suitability for a target species as well as to quantify spatio-temporal shifts as environment changes. These modeling approaches are flexible (e.g., can use presence-only data) and are applicable at different spatial scales with readily-available climatic datasets. Using SDMs, we linked the distribution of I. typographus in Eurasia with biologically-relevant climatic variables that likely play important roles in limiting the distribution of this insect. We then projected the potential distributions of I. typographus in North America. Our results suggest that climatic suitability will improve in the future for I. typographus compared with the current conditions and that northward shifts in suitable climates will occur under climate change.
Emigration or Establishment? Exploring mountain pine beetle range expansion into whitebark pine in British Columbia
Michael Howe, Allan Carroll, Claudio Gratton, Kenneth F. Raffa
Warming temperatures are allowing native insect herbivores to expand into regions that previously exceeded their thermal tolerance. Latitudinal and elevational range expansions are yielding new insect-plant interactions that can fundamentally alter ecosystem processes. Bark beetles cause the most widespread mortality to conifers globally but are limited in their range by host availability and minimum temperatures. Recently, several beetle species have expanded their geographic ranges to cause significant mortality to naïve and semi-naïve host tree species. However, it is unknown whether these expansions are caused by emigration from the historical host, or establishment within the newly accessed range. We tested these two non-mutually exclusive hypotheses by compiling publicly available data which had spatially-explicit information on mountain pine beetle (Dendroctonus ponderosae Hopkins, MPB) infestations in British Columbia on its primary historical host, lodgepole pine (Pinus contorta), and the beetle’s expansion into high-elevation areas with endangered whitebark pine (Pinus albicaulis) communities. Data were compiled over a 20-year period, from 2000-2019. We constructed random-forest models predicting mountain pine beetle infestation severity as a function of geographic location, stand characteristics, regional bioclimatic data, cold suitability metrics, and estimates of beetle propagule pressure.
Moderator: Ashley Schulz
Functional traits drive bee community responses to habitat variability in managed southeastern forests
Christine Cairns Fortuin, Kamal JK Gandhi
Human management of forest systems generates multiple variables which can influence wild bee communities including the creation of gaps and edges, variations in canopy openness, removal or accumulation of dead wood, and variations in depth of soil organic layer. The ways in which wild bees respond to this variability may be mitigated by functional traits such as nesting preferences, diet, seasonality, size, or degree of sociality of wild bee species. To understand how bee communities respond to edges and habitat variability generated by forest management practices, we sampled bees in four replicates of three site-types across a gradient from the edge of a forest road: mature hardwood stands, managed pine stands, and regenerating clearcuts in the Georgia Piedmont. Each site was surveyed for nesting habitat indicators including depth of duff layer, volume of downed wood, decay class of downed wood, and number of standing snags. Regenerating clearcuts had higher alpha diversity of wild bees but displayed higher functional overlap in the bee community that favored soil nesting groups. Hardwood forests provided more nesting niche opportunities leading to higher functional diversity and beta diversity, and instead supported more cavity nesting, softwood nesting, solitary, and early season bees. In contrast, pine forest road edges support a diversity of large-bodied, litter-nesting and specialist bees. Nesting habitat indicators explained 53% of the variation in functional nest guild composition. Overall, results indicate that nesting traits are significant drivers of wild bee community responses to human management in forest systems, and merits consideration in restoration and conservation efforts.
Emerging molecular technologies for bark beetle management
Bethany R. Kyre, Lynne K. Rieske
Bark beetles of the genus Dendroctonus pose a significant threat to coniferous forests worldwide. With 19 species occurring globally, the 5 species found in the United States alone were responsible for over 200 million hectares of damage in 2017 – 2018. Increasingly erratic weather patterns and a history of hands-off silviculture practices have allowed for devastating and persistent outbreaks within the native ranges of Dendroctonus species, as well the invasion into naïve forests outside of their endemic ranges. Emerging molecular approaches involving gene silencing via RNA interference (RNAi) to manage invading populations have proven efficient with both southern pine beetle, Dendroctonus frontalis (SPB), and mountain pine beetle, D. ponderosae, wherein the ingestion of exogenous dsRNAs resulted in near one hundred percent mortality for both species; with additional work focusing on dsRNA efficacy in Ips and wood boring beetles. In addition to the successful activation of the RNAi pathway, assessment of nontarget effects and translocation of exogenous dsRNAs throughout host tissues after root absorption has also been demonstrated, making way for the potential success of tree level protection. However, forest level protection faces additional hurdles. Current efforts are focusing on the role of genetic variation in primer design, and potential methods for landscape level deployment strategies. Although additional work is needed, gene silencing using RNAi provides hope for managing these persistent and recalcitrant forest insects.
Temperature effects on Spotted Lanternfly Phenology
Melody A. Keena, Devin Kreitman, Anne Nielsen, George Hamilton
Lycorma delicatula (White), an invasive planthopper from Asia, is an emerging pest in North America. It is important to understand its phenology in order to determine its potential range in the United States. The lower threshold for egg development was estimated as 7.39°C. Eggs held at constant 10, 15, and 20°C were estimated to require 635, 715, and 849 DD7.39, respectively, to develop. Egg hatch rates were highest when held at a constant 15°C, though high rates were also obtained when eggs were held for 84 days at 10°C, then moved to 25°C. Almost all eggs enter diapause since very few eggs were able hatch when moved to 25°C after 7 days of chill at either 5 or 10°C. Nymphal developmental rate increased with temperature from 15°C to 30°C for all instars, then declined again at higher temperatures. Nymphal survival was lower at 35°C than between 15-30°C for all instars, and first instars placed at 5, 10, and 40°C all died without molting. The lower developmental threshold was found to be 13.00±0.42°C for first instars, 12.43±2.09°C for second instars, 8.48 ± 2.99°C for third instars, and 6.29 ± 2.12°C for fourth instars. The degree-day (DD) requirement for nymphs in the previous instar to complete development to reach the second instar, third instar, fourth instar, and adult was 166.61, 208.75, 410.49, and 620.07 DD (base varied), respectively. These results provide key data to support the development of phenology models and help identify the potential range of L. delicatula in North America.
Impact of biological control agents on Canadian emerald ash borer parasitoids
C. J. K. MacQuarrie, M. Gray, G. Jones, T. Ladd
Three biological control agents have been released in Canada for the control of emerald ash borer. These species were released as part of the US-lead effort to reduce the impact of the pest on ash trees in North America. The first releases of Tetrastichus planipennisi were made in 2013 with Oobius agrili and Spathius galinae following in 2015 and 2017. Beginning in 2018 we initiated experiments to examine the impact and dispersal of these parasitoids in the Canadian ash ecosystem. These experiments were intended to determine if the parasitoids were contributing to population regulation, and to determine if and how far the insect has spread. To examine the impact of the parasitoids on population dynamics we used a series of sequential caging studies to partition the attack of parasitoids on resident emerald as borer in some of the oldest release sites. In our dispersal experiment we used pan traps established at 2-30 Km from the oldest release sites to examine dispersal in southwestern Ontario, Canada. The results of these experiments will be used to estimate the contribution of these biological control agents to regulation of emerald ash borer in Canada.
The Effect of Host Plant on the Nymphal Development of Spotted Lanternfly
Devin Kreitman, Melody A. Keena, Anne Nielsen, George Hamilton
Lycorma delicatula (White), an invasive planthopper from Asia, is an emerging pest in North America that was first introduced in 2014. Even though it has a broad host range, it is heavily associated with Ailanthus altissima (Miller). Due to its polyphagous nature, it is important to understand how host plants affects its phenology. Nymphs were reared on the following host plants at a constant 25°C: Acer rubrum (L.), A. altissima, Celastrus orbiculata (Thunberg), Ocimum basilicum (L.), Rosa multiflora (Thunberg), Salix babylonica (L.), and Vitis labrusca (L.). The development rate and weight were compared for nymphs reared on each host. First and second instar nymphs developed at similar rates on all hosts that were tested. It was found that third instar L. delicatula nymphs took longer to develop on S. babylonica than on A. altissima or V. labrusca. Females weighed more and took longer to develop than males in the third and fourth instars. Survival was variable and the number of hosts that it could utilize to complete an instar decreased as instar increased. Implications for phenology modeling was discussed.
Subterranean survivorship, timing of emergence, and potential supplementary diet of Laricobius spp. (Coleoptera: Derodontidae), biological control agents for the hemlock woolly adelgid
Jeremiah R. Foley, Albert Mayfield, Scott M. Salom
Laricobius spp. share the Derodontidae clade with three other family members (Derondontus, Nothoderodontus, and Peltastica) and together, are collectively known as the “tooth-necked” fungus beetles. From the literature, all genera except Laricobius consumes fungi. Laricobius spp. are specialist predators of Adelgidae and presumably no longer feed on fungi. Additionally, Laricobius nigrinus and L. osakensis have been used as biological control agents for the hemlock woolly adelgid (HWA), Adelges tsugae, for the past 16 and 10 years, respectively. Laricobius spp. spends half of their univoltine life cycle within the arboreal habitat of hemlocks and the other half beneath hemlocks, in a subterranean habitat. Most of the literature on Laricobius spp. has focused on their arboreal habitat and few studies have documented their subterranean biology. Historically, lab-rearing these beetles has been limited by significant mortality (~40%) during the subterranean portion of this insects’ life cycle. Herein, we describe the subterranean biology of L. nigrinus and L. osakensis in terms of their supplementary diet and field survivorship.
Great Lakes Basin Forest Health Collaborative: What it’s all about
Rachel Kappler, Courtney Blashka, David Burke, Eboni Hall, Carolyn Pike, Jennifer Koch
Eastern forests including those in the Great Lakes basin, have been severely impacted by invasive insects and diseases culminating in decreased biodiversity, altered forest ecology, and reduced ecosystem services. Five native ash species (Fraxinus spp.) are threatened with extinction as a result of the emerald ash borer (Agrilus planipennis) including green ash (F. pennsylvanica), an important riparian species and black ash (F. nigra), the loss of which has the potential to convert northern wetland forests to open marsh. Common northeastern forest types containing beech (Fagus grandifolia) and eastern hemlock (Tsuga canadensis) are under siege from beech bark disease, beech leaf disease, hemlock woolly adelgid (HWA), and elongate hemlock scale. The newly formed Great Lakes Basin Forest Health Collaborative (GLB FHC), a partnership with Holden Forests & Gardens, American Forests and the USDA Forest Service, was formed to help advance resistance breeding for these important tree species. The primary mission is to use a participatory approach by establishing a network of partners and provide training and technology transfer. In turn, partners provide volunteers and other resources to work together with the FHC on activities including the identification of survivor trees with potential resistance, clone bank and/or seed orchard establishment, and seed collections, with the long term goal of producing improved seed sources to restore impacted forests. We are currently developing a partner network within the GLB for initial projects that include the identification and propagation of lingering ash trees that have survived long term EAB infestation and seed collections for conservation of eastern hemlock. We anticipate expanding to projects in the future that involve breeding for HWA resistance and identifying beech trees that remain healthy in areas heavily impacted by beech leaf disease. Once networks are established, the FHC can quickly mobilize to address new damaging pests as they arise.
Noon – Lunch (on own)
1:30 p.m. – Concurrent Sessions 3
Moderator: Chris MacQuarrie, Sandy Smith
This symposium presents: When Do Old Plays Work and When Do We Need to Rewrite Them? Managing insect populations can be thought of developing a playbook of tactics and strategies that seek to exploit weaknesses in the pest’s defenses. When we encounter new pests or new outbreaks of old pests we often draw on the successful plays from the past. However, under climate change, range expansions and invasions of new pests sometimes those old plays may not always work. Using examples from previous successful management of native and invasive pests we will examine how these successful plays have influenced the management of more recent pest problems, and where the old playbook has needed to be rewritten.
You shall not pass! Using knowledge on population dynamics to manage spruce budworm
Over the last several decades, much has been learned on the ecology, population dynamics, and management of the spruce budworm in eastern Canadian boreal forests. Evidence increasingly supports the idea that this insect is indeed regulated by a multiple-equilibrium system, where populations are kept in check by natural enemies until they escape and rise to outbreak level where negative feedbacks limit their further growth and eventually cause their decline. All of this occurring in a context of high mobility, connecting regional meta-populations through moth migration. We will discuss the evidence for these statements, the ongoing research and modeling, and their implications for pest management.
The role of native natural enemies in the successful biological control of winter moth in the northeastern United States
Hannah J. Broadley, Joseph S. Elkinton, George H. Boettner
Winter moth, Operophtera brumata, a polyphagous caterpillar was accidentally introduced to the northeastern United States in the 1990s. Previous invasions of winter moth in Canada were successfully suppressed following the introduction of two biological control agents winter moth’s native range: Cyzenis albicans and Agrypon flaveolatum. In our work, we did not use A. flaveolatum due to concerns about its host specificity. We established C. albicans at sites across the northeastern U.S. and establishment has coincided with a dramatic decrease in winter moth density. However, this success depends on additional mortality from native natural enemies including predators and parasitoids. In the native range of Europe, pupal predators were found to regulate winter moth densities. Further, in the two invasive populations of winter moth in Canada, predation was found to increase following the introduction of the biocontrol agents. We built on this earlier research and, over five field seasons, deployed winter moth sentinel pupae in the field to determine rates of predation and parasitism across a range of winter moth pupae and C. albicans puparia densities. Prior to the establishment of C. albicans in years when winter moth densities were high, we did not observe density dependent mortality. Since 2016 however, C. albicans has become widely established and winter moth densities have decreased to a level comparable to what was found it its native range. We have found that mortality on the pupae was density dependent and thus may stabilize winter moth at low density. Overall, our research shows that mortality on winter moth pupae was already high in the northeast but that the introduced biocontrol agent provides enough additional mortality to render winter moth a non-pest.
A new strategy for an old pest: the early intervention strategy against the spruce budworm
Véronique Martel, Rob Johns
The spruce budworm (SBW), Choristoneura fumiferana (Lepidoptera: Tortricidae), is an old pest, but with cyclic outbreaks occurring every 30-40 years. Each outbreak is slightly different, depending on the forest composition, the climate or our use of the forest. Although SBW management has started as early as in the 1950s, the strategies used have changed radically through time: from broad-spectrum insecticides like DDT to more specific biopesticides like Btk, our environmental concerns have transformed pest management. In addition to the change in insecticides used, we also have a better understanding of the population dynamics of this pest, helping us elaborate new strategies. The Early Intervention Strategy has been tested since 2014 in New Brunswick as a way to affect SBW populations, preventing them from rising, instead of limit the impact of high density populations on the forests. The history of SBW management, our understanding of population dynamics and the success of the Early Intervention Strategy against the SBW will be presented.
(Wood) boring phenology for the interest of emerald ash borer invasion management
The invasive emerald ash borer has forever altered the eastern forests of North America. Phloem-feeding larvae have strangled ash, Fraxinus, in 35 US states and five Canadian provinces. Tracking life-stage specific development in growth chambers across biologically-relevant temperatures will increase the accuracy of phenology-based predictions. These growth rates will inform models to mitigate range expansion and predict long-term impacts. For eggs and larvae, 7 and 10 °C appear to be below developmental thresholds with zero eggs hatching and no larvae progressing to second instars. Egg development duration was shorter as temperatures increased from 15 to 35 °C (62 versus 8 days). Larval development within F. pennsylvanica was faster at 30 °C than at 25 °C with more than 50% of larvae completing development from eclosion to prepupae at 30 °C in 45 days. At 30 °C, larvae took residence in mini-bolts at a higher rate in F. pennsylvanica (3.31 ± 0.19 larvae/mini-bolt) compared to F. excelsior (1.13 ± 0.13). Larval development to the first prepupa took 50% longer in F. excelsior than F. pennsylvanica. Future work will include more temperatures for both ash species and compare host differences on growth rates. These growth rates will be used to determine where a life cycle can completed and to enhance biological control release timing.
This workshop will help attendees develop photography skills that are useful for publications, extension/outreach work, and recreational fun. The goals are to learn specifics on, 1) composition, such as depth of field, lines, contrast, viewpoint, depth, negative and filled space, and lighting, 2) become familiar with photography equipment and settings both on cell phones and cameras, and 3) get hands on training and feedback.
- General photography
- Macrophotography and equipment
Moderator: Enrico Bonello
Wicked problems are those that lack a singular solution and change in response to attempts to solve them. Invasions of forest environments by insect pests and pathogens are definitely a wicked problem. The organizational infrastructure for combating such invasions is decentralized, with responsibilities spread across multiple public and private entities, and as a result, incapable of protecting forest resources. Recent advances, e.g. in host resistance breeding, show promise as tools to rapidly and effectively deal with invasive forest pathogens, but as seen with infectious diseases such as the current COVID-19 pandemic, even the most promising solutions face serious implementation challenges. The COVID-19 pandemic highlights the perils of lack of national and global coordination in combating sinister, destructive pests, and may add needed perspective to the discussion of international approaches to combat invasive forest pests. This symposium will be a forum to discuss fresh solutions to this pernicious issue.
- What is wickedness and how does it apply to the forest health crisis?: Geoff Williams, Damian Adams
- Assessing and managing invasive species: The need for a global framework: Matt Ginzel
- Engaging stakeholders in advocating promising strategies to curb destructive non-native pests: Faith Campbell
- Reducing the importation of forest pests and pathogens through Tree-Smart Trade: Gary Lovett
- Using collective actions to address a social dilemma: Insights from invasive plant management by private forest landowners: Zhao Ma
Moderator: Bill Riel
Impacts of mountain pine beetle outbreaks on the structure and composition of and snag longevity in lodgepole pine forests
Jackson P. Audley, Christopher J. Fettig, A. Steven Munson, Justin B. Runyon, Leif A. Mortenson, Brytten E. Steed, Kenneth E. Gibson, Carl L. Jørgensen, Stephen R. McKelvey, Joel D. McMillin, Jose F. Negrón
Following historic mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae), outbreaks in the Intermountain West, US, 2004-2012, we investigated resulting tree mortality and the effects on forest structure and composition. A network of 125, 0.081-ha circular plots was established in lodgepole pine, Pinus contorta, forests in Colorado, Idaho, Montana, Utah, and Wyoming. Plots were installed in 2010 and sampled annually through 2019. 5107 trees died across the network, 98.6% of which were lodgepole pine. Most of the observed tree mortality (68.8%) was attributed to D. ponderosae. The resulting mortality significantly reduced mean diameters at breast height (dbh; by 5.3%), quadratic mean diameter (by 8.6%), tree height (by 15.9%), numbers of trees (by 40.8%), basal area (by 52.9%), and stand density index (by 51.8%). Tree density significantly declined for all diameter classes (5-cm classes) except for the smallest (7.5-12.5 cm). Subalpine fir, Abies lasiocarpa, was well represented in the understory regeneration. We observed more A. lasiocarpa than P. contorta seedlings (≤0.3 m tall) in all states except Montana. An increased number of A. lasiocarpa saplings (>0.3 m tall and <7.6 cm dbh) contributed to the increase in the number of saplings observed across all states from 2010 to 2018. The number of snags (standing dead trees) increased substantially (by 1324.7%). Interestingly, 75.3% snags remained standing in 2019, prompting an interest in understanding snag longevity. We modeled snag fall rates using a Cox’s proportional hazard model to estimate retention time and identify factors contributing to snag fall. Our model predicted a half-life of 16 years for lodgepole pines killed by D. ponderosae. Northern facing aspect was the most significant factor in prolonging snag retention. Snag height was also positively correlated with longer retention times except when a snag had a greater height to diameter ratios (i.e., tall with small dbh).
Elongate hemlock scale in Michigan: distribution, impacts, and natural enemies
Toby R. Petrice, Therese M. Poland, F. William Ravlin
Elongate hemlock scale, Fiorinia externa Ferris (Hemiptera: Diaspididae), is an invasive pest of eastern hemlock trees. This insect has been established in the Northeastern U.S. since the early 1900s but has just recently been discovered in Michigan. Managers are concerned about the impacts this pest may have on eastern hemlock and other host species in the Great Lakes region. In 2020, we initiated studies in Michigan to determine 1) the distribution and impacts of elongate hemlock scale on eastern hemlock and other host species (Picea spp., and Abies spp.); and 2) the presence and impacts of natural enemies on elongate hemlock scale. At two locations where elongate hemlock scale is established in Michigan, we recorded elongate hemlock scale density, lifestages present, parasitism, predators, and hemlock shoot growth. We found that elongate hemlock scale was present on almost all trees at each site and scale infestations on individual trees ranged from very high (182 scales/100 needles) to low (2 scales/100 needles). Most live elongate hemlock scales overwintered as adult females with or without eggs; however, all life stages could be found at any given time during the season. To date, elongate hemlock scale has not been recovered from non-hemlock hosts (Picea spp. or Abies spp.) at survey sites. The scale parasitoid, Encarsia citrina Craw (Hymenoptera: Aphelinidae), was recovered from both sites with overall parasitism of female elongate hemlock scale averaging 44 %. We also recovered the predatory scale picnic beetle, Cybocephalus nipponicus (Endrödy-Younga) (Coleoptera: Cybocephalidae) from both sites.
Why isn’t hemlock woolly adelgid killing trees in its native range? The role of insect predators in managing hemlock woolly adelgid
Ryan S. Crandall, Joseph S. Elkinton, Jeffrey A. Lombardo
For decades, hemlock woolly adelgid (HWA), Adelges tsugae, has devastated hemlocks (Tsuga spp.) in the eastern United States. Fortunately, the HWA biological control program has successfully established predatory beetle Laricobius nigrinus at many sites in the eastern U.S. However, recent studies have shown that although L. nigrinus exerts significant predation rates on the HWA spring generation, overall densities of HWA were not reduced. To better understand host tree and natural enemy influences on HWA populations in its native range, we conducted a predator exclusion study at the Washington Park Arboretum in Seattle, Washington. Using native western hemlock (Tsuga heterophylla), as well as plantings of mature eastern hemlock (Tsuga canadensis), we tested the effects of predation, as well as tree species, on the survival of HWA cohorts experimentally inoculated on pairs of branches. Predators were excluded on one branch of each pair with mesh bags. In both rounds of experiment, after successful inoculation of equivalent densities of HWA spring generation on both pairs of branches, we found that western HWA settled preferentially on western hemlock and that insect predators were responsible for significantly reducing and maintaining low densities of HWA on branches without bags. Round two results suggest that summer-active predators were responsible for significant reduction of the HWA spring generation. Our results demonstrate the importance of summer-active predator acting on the spring generation in reducing HWA densities. We also found that tree resistance did not play a significant role suppressing HWA densities as shown by HWA readily colonizing western hemlock.
Formation of stable hybrid zone between the invasive winter moth and the native Bruce spanworm in eastern North America
Jeremy C. Andersen, Nathan P. Havill, Joseph S. Elkinton
Winter moth (Operophtera brumata) is a non-native invasive species that causes widespread defoliation to a number of forest, ornamental, and orchard tree and shrub species. Beginning in 2007 we established a transect along Route 2 in Massachusetts and in 2016 we established a transect along Route 1 in Connecticut in an effort to 1) document the westward spread of winter moth into the interior portions of New England, 2) to examine the presence of a hybrid zone, and 3) to identify abiotic factors associated with the spread of winter moth. Along our Route 2 transect, the leading edge of the winter moth invasion (i.e., where 10% of individuals were estimated to be winter moth) expanded at a rate of 5.48 ± 3.75 km/year while the core population (i.e., where 90% of individuals were estimated to be winter moth) moved 1.40 ± 3.48 km/year during that same period. In contrast along Route 1 in Connecticut the leading edge retreated 14.7 km while the core population expanded 18 km in the three years of study. Along both transects we documented extremely high levels of hybridization with an average observed hybridization rate of 5.9 ± 0.7% across Route 2 and 4.9 ± 1.9% across Route 1. Our results indicate that while dynamic in nature, winter moth continues to spread westward into the interior portions of New England and that it has the potential become an important defoliator across much of the northeastern United States. Our documentation of a stable hybrid zone with high levels of genomic interchange between winter moth and Bruce spanworm suggests that the introgression of adaptive alleles is occurring, though what effect this has on the pest status of each species remains to be seen.
Abnormally high rainfall may cause regional hemlock woolly adelgid decline in the northeastern U.S.
Jennifer L. Chandler, Joseph S. Elkinton, David A. Orwig
The exotic invasive forest pest, hemlock woolly adelgid (HWA; Adelges tsugae) is the cause of widespread hemlock (Tsuga spp.) mortality throughout the eastern United States. Since its arrival in the northeastern U.S. in the 1980’s, HWA has steadily spread throughout eastern hemlock (T. canadensis) stands. However, in 2018, anecdotal evidence suggested a sharp, widespread HWA decline in the northeastern US following a summer of heavy rainfall. To quantify this decline in HWA density and investigate its cause, we re-surveyed HWA in hemlock stands along a long-term HWA-monitoring transect from northern Massachusetts to southern Connecticut. As previous research documented presence of native fungal entomopathogens on HWA in New England and rainfall is known to facilitate the propagation and spread of fungus, we hypothesized that heavy rainfall may facilitate fungal infection of estivating nymphs of the sistens generation leading to a decline in HWA density. We tested this hypothesis by applying a rain-simulation treatment to hemlock branches with existing HWA infestations in western MA. Our results indicate a regional-scale decline and subsequent rebound in HWA density that correlates with rainfall at each site. Experimental rain treatments led to higher proportions of diseased and dead estivating nymphs compared to controls. This observational and experimental evidence of a rainfall-mediated HWA decline, in conjunction with no evidence for increased winter mortality, implicate heavy rainfall as the cause of the regional-scale drop in HWA density. Isolation of the fungal pathogen(s) responsible for this HWA mortality is underway and may lead to identification of novel biocontrol agents.
Emerald ash borer adult feeding preferences and larval performance on susceptible and “lingering” ash tree selections
Therese M. Poland, Jennifer L. Koch, Kathleen Knight, David Carey, Mary E. Mason, Toby R. Petrice
The emerald ash borer (EAB), Agrilus planipennis, is the most destructive invasive forest insect pest ever to have invaded North America. It was first detected in 2002 near Detroit Michigan and has since spread to 38 states and 5 Canadian provinces where it has killed hundreds of millions of ash trees in urban and natural forests and threatens the entire ash resource. In its native range in far eastern Russia, northern China, Japan, and Korea, it is generally only a pest of non-native ash or indigenous ash species that are stressed by other factors. Long term monitoring plots established in forested areas throughout Ohio and southeast Michigan, helped to identify surviving ash that may have reduced susceptibility or increased resistance to EAB. Individual “lingering” ash trees were selected for propagation and further experimentation that were 10 cm DBH or greater, had healthy canopies, and had survived for at least two years after stand mortality due to EAB exceeded 95%. Subsets of these select surviving trees were used in bioassays to determine EAB adult host choice and feeding preferences and larval development and survival. We compared the number of adults present on leaves of different lingering ash genotypes and susceptible controls as well as the area of foliage consumed in multiple choice experiments using cut leaves in screen cages or sleeve cages on pairs of live potted trees in a greenhouse. We also compared larval weight, developmental stage, and the number of larvae killed by host tree defenses by affixing eggs onto grafted ramets of lingering ash selections and susceptible controls. Our results demonstrate that some selections were significantly less preferred for feeding by EAB adults. Similarly, several lingering ash selections also displayed resistance to EAB through reduced larval weight, delayed larval development, and/or larger numbers of larvae killed by host tree defenses. These measurable phenotypes likely explain why some ash genotypes have survived EAB attack longer than the majority of their counterparts, and indicate that more than one mechanism may be responsible. Clone tests of lingering ash genotypes have been planted to assess field performance relative to the bioassay results. Genetic studies are underway to develop a breeding program to generate seed improved for EAB resistance, appropriate for ash restoration plantings.
N.F. Quinn, J.S. Gould, C.E. Rutledge, J.S. Elkinton, J.J. Duan.
Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), or emerald ash borer, is an invasive wood-boring pest of ash trees (Fraxinus spp.) in the US. It is responsible for catastrophic decline of ash in urban and forested ecosystems, resulting in millions of dollars in injury and losses. Biological control is thought to be one of the most promising management options available to reduce A. planipennis spread and impact. To this end, from 2015 to 2017 two larval parasitoids of A. planipennis from its native range, Spathius galinae Belokobylskij & Strazenac (Hymenoptera: Braconidae) and Tetrastichus planipennisi Yang (Hymenoptera: Eulophidae), were released in wooded areas in New York and Connecticut. The purpose of this study was to measure the long-term spread and phenology of the released parasitoids. From May to September 2020, sentinel ash logs containing EAB larvae were deployed in naturally occurring A. planipennis-infested trees at each release site. Additional logs were deployed in 2 km intervals up to 14 km away from the release site. Logs were replaced every two weeks and the parasitization rate was recorded. Each month, three trees from each release area were cut and debarked to record A. planipennis infestation levels, natural parasitization rates, and A. planipennis and parasitoid phenology. We observed that both S. galinae and T. planipennisi emerged from the first replicate of logs deployed from the end of May to early June as far as 12 km away from the release site. Parasitization peaked in July and August, with sentinel logs deployed at each distance producing both species throughout the summer until mid-September. Both S. galinae and T. planipennisi were collected 14 km away from the release sites, the greatest distance away from the release sites sampled. Debarked trees produced similar findings, with relatively more immature specimens of both parasitoids collected in May and June, while adults and cocoons were relatively more frequently observed in samples collected from July and August. Our results indicate that the classical biological control program initiated several years ago has successfully produced a self-sustaining population of both S. galinae and T. planipennisi. Additionally, our results suggest that these parasitoids are capable of spreading relatively quickly. This can be used to inform future release efforts, allowing for strategic spacing of release points across geographic regions. Overall, our study suggests that both S. galinae and T. planipennisi may continue to spread, increasing the biological control of A. planipennis over time across spatial scales.
The role of native natural enemies in the successful biological control of winter moth in the northeastern United States
Hannah J. Broadley, Joseph S. Elkinton, George H. Boettner
Winter moth, Operophtera brumata, a polyphagous caterpillar was accidentally introduced to the northeastern United States in the 1990s. Previous invasions of winter moth in Canada were successfully suppressed by the introduction of a parasitic fly Cyzenis albicans from winter moth’s native range. We established C. albicans at sites across the northeastern U.S. and establishment has coincided with a dramatic decrease in winter moth density. However, this success likely depends on additional mortality from native natural enemies including predators and parasitoids. In the native range of Europe, pupal predators were found to regulate winter moth densities. Further, in the two invasive populations of winter moth in Canada, predation was found to increase following the introduction of the biocontrol agents. We built on this earlier research and, over five field seasons, deployed winter moth sentinel pupae in the field to determine rates of predation and parasitism, m across a range of winter moth pupae and C. albicans puparia densities. Mortality on the pupae was high across sites and years (85 to 95%) and is primary caused by a diverse community of generalist ground predators. In years when winter moth densities were high prior to the establishment of C. albicans we did not observe density dependent mortality. Since 2016 however, C. albicans has become widely established and winter moth densities have decreased to a level comparable to what was found in its native range. And we have found that mortality on the pupae was density dependent and thus may stabilize winter moth at low density. Overall, our research shows that mortality on winter moth pupae was already high in the northeast but that the introduced biocontrol agent provides enough additional mortality to render winter moth a non-pest.
3:00 – Break
3:30 – Concurrent Sessions 4
Moderator: Chris MacQuarrie, Sandy Smith
The legacy of managing mountain pine beetle in British Columbia: the science and the policy
The pine forests of British Columbia have experienced many large-scale mountain pine beetle (MPB) outbreaks that have resulted in mortality of hundreds of millions of trees over expansive areas of forest. In response to these landscape-level events, foresters and scientists have developed a suite of management strategies and tactics to mitigate the impacts of MPB. When major infestations of both spruce beetle and MPB erupted in central B.C. in the 1970s and 1980s this prompted the B.C. government to develop a coordinated response, resulting in the creation of the Pest Management Program (now Forest Health); and, so began the battle of the beetles in B.C. When the last, and largest, MPB outbreak on record began to develop in north central British Columbia during the 1990s, federal and provincial governments once again looked to their top scientists for guidance to take on this monumental challenge. In this presentation I will describe intervention techniques used to control MPB, and B.C.’s current strategies that incorporate new technology, modelling, harvesting and scientific insight. I will also highlight the never-ending challenges faced by forest mangers such as sheer physical scale, climate change and the biological, social and political intricacies. But the most pressing questions may be what have we learned and how will our future management of MPB differ?
How have phytosanitary approaches to address forest-product pest management changed?
In the past, pest mitigation of forest products has relied mainly on fumigation and heat treatments to reduce the associated pest risk. Today a wider variety of options are available, including systems approaches, new methods for applying heat treatment and lower dosages of both fumigants and heat. International and regional standards for phytosanitary measures provide guidelines for adoption of new treatments, and options available for appropriate pest-risk reduction measures, with the ultimate goal of reducing the movement of plant pests and protection of forests.
Entomology notes from a small island: impact and management of invasive forest pests in Britain
The spread of invasive species by international trade is a global concern, and Great Britain's long trading history has provided a wealth of opportunity for the accidental (and deliberate) introduction of non-native organisms to its shores. Yet compared with continental Europe and North America, the impact of invasive forest insects in Britain has been relatively limited to date. This talk will explore key introductions and pest threats from recent years, what factors might be limiting more widespread damage, and whether this can help to direct horizon scanning and surveillance activities in an uncertain future.
- How to take photographs with a cell phone, helpful tips, and useful equipment/settings
- How to take photographs with a camera, helpful tips, and useful equipment/settings
- Post-conference feedback on images via email
Moderator: Enrico Bonello
- Genetic Resistance in forest trees: Time to move it to the forefront: Richard Sniezko
- Centers for forest pest control and prevention: Our call to action?: Enrico Bonello
Moderators: Jess Hartshorn, Molly Darr
The symposium will have broad interest in that the proposed speakers’ areas of interest span climate change impacts on tree defenses to insects and pathogens, population genetics of pests in forests, social impacts of forest management, and impacts of invasive species.
Impacts of tree ontogeny and biotic stressors on the composition of secondary metabolites within the phloem tissue of two species of ash (Oleaceae: Fraxinus) in New Hampshire
Since its accidental introduction into North America three decades ago, the invasive emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) has spread rapidly throughout the United States and killed millions of ash trees (Oleaceae: Fraxinus). This has resulted in severe ecological damage to natural and managed forests and economic losses exceeding billions of dollars. While most North American ash that are attacked by A. planipennis die, there is increasing evidence that some trees have the capacity to resist the beetle for longer periods of time, or to avoid attack altogether. This pattern is exemplified in smaller diameter ash trees where A. planipennis experience reduced levels of larval survival relative to larger trees of the same species. Here we report on our ongoing study to understand how ontogeny influences the composition of constitutive secondary metabolites, and how artificial infestation by A. planipennis and application of the plant hormone methyl jasmonate may interact with ontogeny to alter these chemical profiles within the phloem of green (Fraxinus pennsylvanica) and white (Fraxinus americana) ash across four diameter classes. Preliminary analysis indicates that prior to induction, the composition of secondary metabolites is similar regardless of size class. After induction, there is a large divergence in the composition of secondary metabolites according to size class, which may reflect that defensive strategies of ash are age-dependent. This research will increase our understanding of defensive strategies of Fraxinus, informing horticultural or silvicultural strategies to maintain healthy ash in light of the current invasion by A. planipennis.
The value of hybrid and nonnative ash for the conservation of ash specialists in regions invaded by emerald ash borer
Browntail moth: of all the labs in all the towns, you had to fly into mine
What bugs trees: an interdisciplinary approach to evaluating insect disturbances in western North America
In western North America, disturbances impact thousands to millions of hectares of forests annually, and in many regions, insects are the leading cause. Forest insects can be characterized by their guilds, each leaving their own signature on tree growth, mortality, and ecological patterns and processes. Two insect guilds—bark beetles in the genus Dendroctonus and defoliators in the genus Choristoneura—have extensive ranges throughout North America and in many systems result in significant damage. Bark beetles are tree killers and outbreaks result in large pulses of mortality of their hosts. Thus, outbreaks are a stand releasing disturbance at small spatial scales, and at large spatial scales can reorient successional trajectories across the landscape. Defoliators, on-the-other hand, rarely result in the death of their host, and instead outbreaks result in stand-to-landscape scale suppression signals in the tree-ring record. Here, I evaluate the compositional and structural changes that resulted from extensive bark beetle outbreaks in mixed conifer forests of the Sierra Nevada in California during and after the 2012-16 drought. At the stand scale I will explore how wood anatomical characteristics are modified by a chronic western spruce budworm outbreak in xeric Douglas-fir forests of southern British Columbia.
5:00 - Break
5:30 - Banquet
Not Boring: How digging deep and branching out will shape the future of forest entomology
Kristie Riddick, Bug Chicks