Scientists in New Zealand are saying explicitly that a forest’s unique mixture of species matters when considering the future. This mixture is the result of the forest’s evolutionary history. Losing members of the biological community reduces the forest’s ability to respond to current and future stresses – its resilience.
New Zealand’s forests are part of the broader legacy of the ancient supercontinent of Gondwanaland – the island nation’s plants have close relatives in South America, the Pacific Ocean islands, and Australia. Still, these forests are unique: 80% of New Zealand’s plant species are endemic. The forests are also species-rich. The warm temperate evergreen rain forests of the North Island are home to at least 66 woody plant species that can reach that reach heights above six meters (Simpkins et al. 2024).
These forests have been severely changed by human activity. In just ~ 750 years people have cut down approximately 80% of the original forest cover! (Simpkins et al. 2024) Of the eight million hectares of surviving native forest, a little over five million hectares is managed for the conservation of biodiversity, heritage, and recreation. Another 2 million hectares are plantations of non-native species.
sites in New Zealand where pine plantations are “wilding”
All these forests are challenged by introduced mammals – from European deer to Australian possums. Climate change is expected to cause further disturbance, both directly (through e.g., drought, extreme weather) and indirectly (e.g., by facilitating weed invasion and shifting fire regimes) (Simpkins et al. 2024).
Pathogen threats are also common threats to the native trees of the Pacific’s biologically unique island systems. For example, Ceratocystis lukuohia and C. huliohia (rapid ‘ōhi‘a death, or ROD). The latter is killing ‘ōhi‘a (Metrosideros polymorpha) on the Hawaiian Islands. More than 40% of native plant species in Western Australia are susceptible to Phytophthora cinnamomi. Here I focus on two pathogens, kauri dieback and myrtle rust, now ravaging New Zealand’s native flora. No landscape-level treatment is available for either pathogen.
When considering this suite of challenges, Simpkins et al. focus on these two pathogens’ probable impact on forest carbon sequestration. They worry in particular about erosion of the forests’ resilience due to loss of “ecological memory” – the life-history traits of the species (e.g., soil seed banks) and the structures left behind after individual disturbances.
one of the largest remaining kauri trees, “Tane Mahuta”, in Waipoua Kauri Forest; photo by F.T. Campbell
Kauri Dieback
The causal agent of Kauri dieback, Phytophthora agathidicida, is a soil-borne pathogen that spreads slowly in the absence of animal or human vectors. The disease affects a single species, Agathis australis (kauri, Araucariaceae). However, kauri is a long-lived, large tree that is a significant carbon sink. It probably modifies local soil conditions, nutrient and water cycles, and associated vegetation. Also, kauri has immense cultural significance.
Simpkins et al. note that kauri dieback threatens stand-level loss of A. australis – that is, local extinctions. In the absence of disturbance Kauri trees can grow to awe-inspiring size. In the 19th Century, before widespread logging, some were measured at 20 meters or more in circumference. Consequently, kauri dieback might cause a decline in aboveground live carbon storage of up to 55%. This loss would occur over a period of hundreds of years, not immediately.
Huge kauri are not likely to be replaced by other long-lived emergent conifers (based on an analysis of one species, Dacrydium cupressinum). Instead, kauri are probably going to be replaced by late-successional angiosperms. The authors discuss the ecological implications for levels of carbon storage and proportions of trees composed of Myrtaceae – exacerbating damage caused by myrtle rust (see below).
The expectation of Simpkins et al. that kauri will suffer at least local extinctions is based on an assumption that no kauri trees are resistant to the pathogen. Fortunately, this might not be true: different Agathis populations show various levels of tolerance to Agathis dieback. Identification and promotion of some levels of resistance could enable A. australis to retain a diminished presence in the landscape.
However, Lantham, et al. make clear that containing kauri dieback remains “challenging,” despite its discovery nearly 20 years ago (in 2006). Scientists and land managers have little information on the distribution of symptomatic trees, much less of the pathogen itself. This means they don’t know where infection foci are or how fast the disease is spreading.
As is often true, the pathogen is probably present in a stand for years, possibly a decade or more, before symptoms are noticed. This means that the current reliance on public reports of diseased trees, or targetting surveillance on easy-to-access sites (e.g., park entrances and along existing track networks), or at highly impacted areas readily identified through aerial methods, fails to detect early stages of infection. Indeed, it seems probable that P. agathidicida had been present in New Zealand’s ecosystems for decades before its formal identification.
The Waipoua forest is one of the largest areas of forest with old kauri stands in the country. A new analysis of aerial surveys done between 1950 and 2019, shows how the forest is changing. The number of dead trees increased more than four-fold and the number of unhealthy-looking trees increased 16-fold over these 70 years. Kauri dieback is now widespread in this forest, especially in areas near human activities like clearing for pasture or planting commercial pine plantations).
Lantham et al. have developed a model which they believe will help identify areas of higher risk so as to prioritize surveillance and inform responses. These could delimit the disease front and help implement quarantines or other measures aimed at limiting the spread of P. agathidicida to uninfected neighboring sites.
I hope New Zealand devotes sufficient resources to expand surveillance and management to levels commensurate with the threat to this ecologically and culturally important tree species.
Leptospermum scoparia; photo by Brian Gatwicke via Flickr
Myrtle Rust
Myrtle rust is a wind-borne disease that affecting numerous species in the Myrtaceae, including some of the dominant early successional species (e.g., Leptospermum spp.). Simpkins et al. expect that myrtle rust might hasten the decline of two such tree species (L. scoparium and Kunzea ericoides). However, these trees’ small size and rapid replacement by other species during succession minimizes the effect of their demise on carbon storage.
Because I am concerned about the irreplaceable loss to biodiversity, I note that Simpkins et al. also feared immediate threats to some trees in the host Myrtaceae family, specifically highly susceptible species such as Leptospermumbullata.
As I reported in a recent blog, a second group of scientists (McCarthy et al.) explored the threat from myrtle rust more broadly. Austropuccinia psidii has spread through Myrtaceae-dominated forests of the Pacific islands for about 20 years.
Trees in the vulnerable plant family, Myrtaceae, are second in importance (based on density and cover) in New Zealand’s forests. Successional shrub communities dominated by the two species named above, Kunzea ericoides and Leptospermum scoparium, are widespread in the northern and central regions of the North Island and in northeastern and interior parts of the South Island. These regions’ vulnerability is exacerbated by the area’s climate, which is highly suitable for A. psidii infection (Simpkins et al. 2024).
McCarthy et al. concluded that ifLeptospermumscoparium and Kunzea ericoides prove to be vulnerable to myrtle rust, their loss would cause considerable change in stand-level functional composition across these large areas. They probably would be replaced by non-native shrubs, which are already common on the islands. Any resulting forest will differ from that formed via Leptospermeae succession.
These authors also worry that the risk to native ecosystems would increase if more virulent strains of the myrtle rust pathogen were introduced or evolved. They note that A. psidii is known to have many strains and that these strains attack different host species.
SOURCES
Latham, M.C., A. Lustig, N.M. Williams, A. McDonald, T. Patuawa, J. Chetham, S. Johnson, A. Carrington, W. Wood, and D.P. Anderson. 2025. Design of risk-based surveillance to demonstrate absence of Phytophthora agathidicida in New Zealand kauri forests. Biol. Invasions (2025) 27, no. 26
McCarthy, J.K., S.J. Richardson, I. Jo, S.K. Wiser, T.A. Easdale, J.D. Shepherd, P.J. Bellingham. 2024. A Functional Assessment of Community Vulnerability to the Loss of Myrtaceae from Myrtle Rust. Diversity and Distributions, https://doi.org/10.1111/ddi.13928
Simpkins, C.E., P.J. Bellingham, K. Reihana, J.M.R. Brock, G.L.W. Perry. 2024. Evaluating the effects of two newly emerging plant pathogens on North Aotearoa-New Zealand forests using an individual-based model. Ecological Modelling, www.elsevier.com/locate/ecolmodel
Posted by Faith Campbell
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at https://treeimprovement.tennessee.edu/
riparian ash killed by EAB; in this case, Mattawoman Creek in Maryland. Photo by Leslie A. Brice
Good news at the recent 33rd USDA Research Forum on Invasive Species. Scientists presented the first study that demonstrates significantly lower ash tree mortality in sites with high parasitism rates of two larval parasitoids, Tetrastichus planipennisi and Spathius galinae.
Their study area is the ash-dominated riparian area along the Connecticut River that flows north to south across the middle of Massachusetts. Knowing in advance that the emerald ash borer (Agrilus planipennis; EAB) would invade the area, scientists established monitoring plot that consisted of marked individual ash trees. EAB was first detected in the southern reach of the riparian area in 2015. It gradually moved north. By 2020 isolated mortality was observed at all sites. Meantime, they released three biocontrol agents – T. planipennis,S. galinae, and Oobius agrilii – early in the invasion at three of the six monitoring sites. These released occurred in 2018 – 2020 and again in 2022.
In 2021 and 2025, the scientists counted the numbers of biocontrol agents in the marked trees or sentinel logs. Thus the first evaluation occurred six years after EAB arrived, three years after the first releases of biocontrol agents.
They found that at southern Massachusetts sites, where EAB density was higher at the time of the biocontrol agents’ initial release, remaining ash grew more slowly than in the North. They believe the trees’ growth rate was suppressed by the trees having fewer resources. They also observed dieback. Smaller trees grew faster, perhaps responding to opening of the canopy as mature ash succumbed to EAB invasion.
The most important finding was that ash mortality at all sites was ~50% or less … not the 90% expected based on experience in the upper Midwest where the EAB invasion occurred before biocontrol agents were developed.
SOURCE
Ash survival and growth response to emerald ash borer invasion in Massachusetts riparian forests: impacts of biological control. Mitchell A. Reed, Jian Duan, Ryan S. Crandall, Roy G. van Driesche, Jeremy C. Anderson, Joseph S. Elkington. Presentation to the 33rd USDA Interagency Research Forum on Invasive Species, Annapolis, Maryland February 25-28, 2025 (The proceedings should be posted online before the end of the year.)
Posted by Faith Campbell
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at https://treeimprovement.tennessee.edu/
discarded pallets next to developed area in Glacier National Park (!); photo by F.T. Campbell
Since July 2015 I have posted nearly 50 blogs about non-native insects introduced via movement of solid wood packaging material (SWPM). Why? Because SWPM is one of two most important pathways by numbers introduced & by impact of the species introduced. (The other pathway is P4P.) To read those earlier blogs, scroll below “archives” to “categories”, choose “wood packaging”.
dead redbay trees in Everglades National Park; killed by laurel wilt vectored by redbay ambrosia beetle
As I have reported in the earlier blogs and in my “Fading Forests” reports (links at the end of this blog), in 2002, the parties to the International Plant Protection Convention (IPPC) adopted an international “standard” to guide countries’ programs intended to reduce the presence of damaging insects in the wood packaging: International Standard for Phytosanitary Measures (ISPM) #15). The U.S. and Canada adopted the standard through a phase-in process culminating in 2006. [For a discussion of the phase-in periods and process, read either of the studies by Haack et al. cited at the end of this blog.] In other words, the U.S. and Canada have implemented ISPM#15 for almost 20 years. China specifically has been subject to requirements that it treat its SWPM even longer – since December, 1998, i.e., more than 25 years.
Unfortunately, ISPM#15 is not intended to prevent pest introductions. As stated in Greenwood et al 2023, “Prior to 2009, the goal of compliance with ISPM 15 was to render the risk of wood-borne pests “practically eliminated,” in 2009 the standard was amended to “significantly reduced”.
Despite almost universal adoption of the standard by countries engaged in international trade, insects have continued to be present in wood packaging. A very high proportion of these infested shipments — 87% – 95% — of the SWPM found by U.S. officials bears the ISPM#15 stamp – that is, is apparently compliant. (See my blogs by clicking on the “Category” “wood packaging” listed below the “Archives”.) The same proportion was found in a narrower study in Europe (Eyre et al. 2018). All the post-2006 examples of infested wood analyzed by Haack et al. (2022) (see below) carry the stamp. I conclude that the ISPM#15 mark has failed in its purpose: to reliably indicate that SWPM accompanying imports has been treated so as to minimize the likelihood that an insect pest will be present.
Dr. Robert Haack, retired USFS entomologist, has twice tried to estimate the “approach rate” of insects in SWPM entering the United States (both studies are cited at the end of this blog). A study published in 2014 that relied on data from 2009 found that U.S. implementation of ISPM#15 was associated with a reduction in the SWPM infestation rate reported of 36–52%. The authors estimated the infestation rate to be 0.1% (1/10th of 1%, or 1 consignment out of a thousand). (See Haack et al. 2014; citation at the end of this blog.)
In their second study, published in 2022, Haack and colleagues found a 61% decrease in rates of borer detection in wood packaging when comparing numbers of wood borer detections in 2003 – before the U.S. implemented ISPM#15 – to those in 2020. Specifically, detections dropped from 0.34% in 2003 to 0.21% in 2020. This decrease occurred despite the volume of U.S. imports rising 68% between 2003 and 2020. (My blogs document a further increase in import volumes over the years since 2020.) In addition, the number of countries from which the SWPM originated more than doubled from 2003–2004 to 2010–2020. This expansion exposes North America to a wider range of insect species that might be introduced, as well as a wider range of individual countries’ effectiveness in enforcing the standard’s requirements (Haack et al. 2022).
These decreases are encouraging. However, Haack et al. (2022) note some caveats:
The reduction in pest presence was greatest during the initial implementation of the program the first phase, 2005-2006 (61%); in subsequent periods pest approach rate inched back up. In the 2010-2020 period, the pest detection rate was only 36% below the pre-ISPM#15 level. Detection rates have been relatively constant since 2005. Does this stasis mean that exporters learned that they could ignore or circumvent the requirements without suffering significant penalties? Or is some of this rise related to increased trade volumes, increasing variety of country of origin for trade, or other global trade patterns unrecognized in the data? (However, see the next bullet point.)
Certain types of commercial goods and exporting countries have consistently fallen short. Specifically, the rate of wood packaging from China that is infested remained relatively steady over the 17 years since 2003. The proportion of consignments with infested wood packaging coming from China was more than five times the proportion of all inspected shipments for this period. In other words, China has had a consistent record of poor compliance with phytosanitary regulations since they were imposed in December 1998. Why is USDA not taking action to correct this problem? (As I note below, DHS CBP has ramped up enforcement efforts.) Some other countries, e.g., Italy and Mexico, have reduced the rate at which wood packaging accompanying their consignments is infested. In fact, Mexico’s improved performance largely explains the overall infestation rate estimate of 0.22% during the period 2010-2010. Mexico’s successes affect the overall statistics in a way that makes other countries’ failure to reduce the presence of pests in wood packaging they ship to the United States far less obvious.
Haack et al. (2022) discuss ten possible explanations for their finding that pest approach rates – as determined by their study — have not decreased more. See the article or my blog about the study.
Although USDA APHIS has not taken steps to strengthen its enforcement, U.S. Customs and Border Protection [an agency in the Department of Homeland Security] has done so twice — see here and here. CBP staff have expressed disappointment that these actions reduced the numbers of shipments in violation of ISPM#15 by only 33% between Fiscal Year 2017 and FY2022. True, more than 60% of these violations consisted of a missing or fraudulent ISPM#15 stamp. However, 194 consignments still harbored live pests prohibited under the standard.
APHIS did agree in 2021 to enable the study by Robert Haack and colleagues, via an interoffice data sharing agreement between USDA APHIS and the Forest Service- this resulted in Haack et al. 2022.
APHIS and CBP also collaborated with an industry initiative to train inspectors that insure other aspects of foreign purchases. The ideas was that CBP or APHIS and their Canadian counterparts would inform importers about which foreign treatment facilities have a record of poor compliance or suspected fraud. The importers could then avoid purchasing SWPM from them. I have heard nothing about this initiative for three years, so I fear it has collapsed.
We lack data on which to base a rigorous analysis
While the two studies by Robert Haack and colleagues are the best available, and they relied on the best data available, the fact is that those available data do not provide a full picture of the risk of pest introduction associated with wood packaging. As pointed out by Leigh Greenwood of The Nature Conservancy in her presentation to 2025 USDA Invasive Species Research Forum, available data have been collected for different purposes than to answer this question. Leigh’s powerpoint is posted here.
Leigh has identified the following data gaps:
In their studies, Haack and colleagues rely on data from the Agriculture Quarantine Inspection Monitoring (AQIM) system. This dataset is based on random sampling of very distinct segments of incoming trade. It is therefore a better measure of insect approach rates than reports of interceptions by either APHIS or CBP.
However, AQIM includes data from only those very distinct segments of trade: perishable goods, SWPM associated with maritime containerized imports, Italian tiles, and “other” goods, AQIM does not contain a segment of trade that includes wood packaging associated with maritime breakbulk or roll-on, roll-off (RORO) cargo. These exclusions have prevented scientists and enforcement officials from determining, inter alia, how great a risk of pest introduction is associated with various types of wood packaging, especially dunnage, as the randomized sample does not include entire pathways for the entrance of dunnage.
Greenwood states that she has not found another country that operates a similar analysis of randomly collected data at ports of entry.
2) USDA does not collect data on consignment size, piece-specific infestation density, nor consignment-wide infestation density. As Haack et al. (2022) point out, reporting detections by consignment doesn’t reveal the number of insects present. If implementation of ISPM#15 resulted in fewer live insects being present in an “infested” consignment, this would reduce the establishment risk because there is lower propagule pressure. However, we cannot know whether this is true.
3) Neither USDA nor CBP reports the inspection effort. Nor do they conduct a “leakage survey” to see how often target pests are missed. This means, inter alia, that we cannot estimate inspectors’ efficiency in detecting infested wood packaging. If their proficiency has improved as a result of improvements in training, inspection techniques, or technology, the apparent impact of ISPM#15 would be under-reported in recent years.
4) USDA does not require port inspectors to report the type of SWPM in which the pest was detected. Leigh participated in an effort that included industry representatives, DHS CBP and USDA APHIS to define the types of wood packaging in legal terminology so that they could be incorporated in the drop-down menu on inspectors’ reporting system. This was first successfully included in the legal glossary within USDA APHIS system of record, ACIR Glossary. Last fall the team was working to integrate the requirement for using these definitions into the inspection data collection system used by DHS CBP, which would then make this data available in Agricultural Risk Management, ARM (see Abstract here for adequate primer on ARM). However, it is unclear now whether the new administration will do so. One potential barrier is that asking the port of entry inspection staff to record these data will add to the time and training required for reporting inspection results.
In summary, Leigh reports that current data systems do not support
estimating probabilities of pest infestation of via volume or type of SWPM (e.g. pallet vs dunnage)
measuring the risk of arrival associated with a specific hazard (in this case, a hazard being a live pest or pathogen associated with SWPM)
extrapolating or supporting findings for some types of wood packaging to other types of wood packaging
Scientists from Canada, Mexico, and the United States have formed a working group under the auspices of the North American Plant Protection Organization (NAPPO). The group is trying to determine whether various types of wood packaging are more likely to harbor pests. This study is currently hampered by the many data gaps, including those Leigh outlined above. The best data available, cited by Haack et al. (2022), found that in maritime containerized shipping, crates were more likely to harbor pests than pallets- however, other forms of SWPM (dunnage, bracing, etc.) had such low sample size that no analysis of those is possible. One of the main objectives of the NAPPO study is to evaluate if dunnage poses the same or higher risk, so this is a major impediment.
Two issues need to be resolved.
One is scientific: why are insects continuing to be detected in wood packaging marked as having been treated? What is the relative importance of insects surviving the treatment versus treatment facilities applying the treatments incorrectly or inadequately?
The second issue is legal and political: what proportion of the detections is due to treatment facilities committing outright fraud – claiming to treat the wood, stamping it with an IPPC stamp, while not actually performing any treatments at all?
Knowing which measures will most effectively solve these quandaries / reduce pest presence in wood packaging depends on knowing what the relative importance of these factors are in causing the problem. The lack of basic data on which to base any analysis certainly hampers efforts to improve protection.
Leigh calls for researchers to recognize these data needs and work to fill them.
•Understand, account for, and communicate data realities
•Work collectively to increase useable data quality
•Use additional research to validate, or to demonstrate disparities
Why Wait for the Science?
In the meantime, however, I assert that more vigorous enforcement efforts by responsible agencies should help reduce the occurrence of fraud. I have suggested the following actions:
U.S. and Canada refuse to accept wood packaging from foreign suppliers that have a record of repeated violations – whatever the apparent cause of the non-compliance. Institute severe penalties to deter foreign suppliers from taking devious steps to escape being associated with their violation record.
APHIS and CBP and their Canadian counterparts follow through on the industry-initiated program described above and here aimed at helping importers avoid using wood packaging from unreliable suppliers in the exporting country.
Encourage a rapid switch to materials that won’t transport wood-borers. Plastic is one such material. While no one wants to encourage production of more plastic, the Earth is drowning under discarded plastic. Some firms are recycling plastic waste into pallets.
Posted by Faith Campbell
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at https://treeimprovement.tennessee.edu/
Reminder: beech leaf disease (BLD) came to attention in 2012 near Cleveland. It has since spread rapidly to the East and more slowly to the North, South, and West. It has been detected in 15 states and the Province of Ontario. The disease is caused by the foliar nematode Litylenchus crenatae mccannii (Lcm). Damage to the leaves can significantly reduce the tree’s ability to photosynthesize, resulting in a progressive depletion of carbohydrate reserves following successive years of infection. Scientists continue efforts to determine how it is spread and the extent of tree mortality.
Last summer I blogged about an Integrated Pest Management (IPM) strategy developed by Bartlett Tree Research Laboratories – the research arm of Bartlett Tree Experts – to treat individual beech trees afflicted with beech leaf disease (BLD). This treatment relied on a foliar spray. The challenge is that the entire canopy must be sprayed; this is difficult for large trees. Also, some trees cannot be sprayed because of their proximity to water bodies or other issues. For these large trees, Bartlett sought to develop a systemic treatment that can be applied as a drench or root flare injection.
photo by Matt Borden, Bartlett, via Flickr
I rejoice to tell you that Bartlett has now confirmed effectiveness of a systemic root flare injection treatment. Again, the project is led by Dr. Andrew Loyd and Dr. Matthew Borden. The full citation for their publication is at the end of this blog.ph
This second treatment utilizes Thiabendazole (TBZ), which has a long history of use in arboriculture to manage Dutch elm disease and sycamore anthracnose. In addition to being a fungicide TBZ is also a potent nematicide.
Bartlett tested the efficacy of TBZ by monitoring 62 symptomatic American beech (Fagus grandifolia) trees across three sites comprising natural mixed hardwood forests with beech as a dominant species. Half of the trees were injected with TBZ, and the rest were monitored as non-treated controls. In the late winter after applying the injection, the researchers sampled twigs from all the trees and counted the number of nematodes in late-season dormant buds, where most of the damage occurs. They also quantified canopy density and BLD symptom expression before treatment and around 11 months after the tree injections the following year, to gauge year-over-year change. At one site, in Ohio, the trees were assessed again in the second season, or 22 months, after the initial injection. They also assessed damage to the root flare caused by the injection process.
Bartlett’s researchers found that at both 11 and 22 months after treatment, injected trees had significantly better visual ratings of canopy condition and lower numbers of Lcm in dormant buds. The untreated controls continued to have high disease severity and large numbers of nematodes in their buds.
Detailed Results
At the time of the initial inventory and treatment, about 65% of the canopies of beech trees at the two Ohio sites displayed foliar BLD symptoms. The proportion was lower at the New Jersey site, where BLD has been present only a season or two before treating – 42%.
During the first growing season post-treatment, the percent of the symptomatic beech canopies at the two Ohio sites fell by 70 – 85%. At the site where trees were evaluated again the second season (22 months) post-treatment, the percent of the canopy exhibiting leaf symptoms continued to decline. The scientists hypothesize that this continuing decrease could be due to TBZ residues being translocated to new leaves and buds, or to a reduction in local inoculum sources within the individual trees and surrounding forest due to treating a significant portion of the community.
At the New Jersey site, where injection was performed later in the season, the percent of the canopy exhibiting leaf symptoms increased by 66%. However, by another measure – percent of canopy with fine twig dieback – these trees improved by 71% while on untreated trees twig dieback increased by 95% and were already experiencing severe canopy loss.
New Jersey site contrasting treated & untreated trees; photo by Matt Borden, Bartlett
On average, there were significantly fewer Lcm in dormant bud tissues in treated trees compared to the untreated control trees. At the two sites in Ohio, the reductions were by 86% and 99%. At the New Jersey site, the decline was not as great, but still encouraging: 70%.
These results suggest that one treatment can substantially reduce symptoms. Scientists now need to determine at what point BLD symptoms return to damaging levels at both “low” & “high” concentrations of thiabendazole in order to determine retreatment intervals and expectations.
While the disease severity (measured by the percent canopy displaying BLD leaf symptoms) of all trees increased at Hillsborough, the canopies of trees injected with the “low rate” of TBZ was significantly better than those of the untreated trees. This was because of a significant reduction in fine twig dieback in the former as opposed to a significant increase in fine twig dieback in untreated controls. Fine twig dieback symptom expression is presumed to be associated with bud abortion caused by Lcm.
The New Jersey treatments occurred at the end of August. The scientists think that this period might follow rather than precede dispersal of many nematodes from the leaves to the buds, as evidenced by the reduced but still substantial numbers of nematodes found in the buds.
While there was some damage visible at injection sites, the Bartlett team considers the frequency of these symptoms to be low. Cracking of the bark was seen on 19% of injected trees; evidence of fluxing was present on 12%. Injection sites were closing rapidly at the site reviewed after 22 months post-treatment. Additionally, based on observations made during this study, they believe that cracking can be further reduced.
Loyd et al. conclude that TBZ injection is an effective treatment option for large beech (> 25-cm dbh) where full coverage sprays with fluopyram are difficult, or for trees growing near water, or where pesticide drift may be of concern.
a forest in Northern Virginia dominated by beech; photo by F.T. Campbell
While this treatment can be used in natural landscapes, treatments of whole forests will probably not be feasible due to the cost. Scientists continue investigating whether some combination of silvicultural practices such as reduction in stand density and with pesticide application of select mature beech might prove effective. In fact, scientists are establishing new plots this year to test a silviculture management approach in forests of Pennsylvania and Rhode Island where BLD is prevalent.
SOURCE
Loyd, A.L., M.A. Borden, C.A. Littlejohn, C.M. Rigsby, B. Brantley, M. Ware, C. McCurry, & K. Fite. 2025. Thiabendazole as a Therapeutic Root Flare Injection for Beech Leaf Disease Management Arboriculture & Urban Forestry 2025 https://doi.org/10.48044/jauf.2025.007
Posted by Faith Campbell
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at https://treeimprovement.tennessee.edu/
The pest alert system “PestLens” has again alerted us to plant pests in Europe or Asia that feed on species closely related to tree species native to North American forests. Two of the insects named in the alert apparently pose a hazard to icons of the forests of America’s Pacific coast forests, giant sequoia and redwood.
I hope APHIS is using this information to alert port and on-the-ground staff and perhaps initiating more in-depth risk assessments.
The posting on February 27, 2025 reported that cotton jassid, Jacobiasca lybica (Hemiptera: Cicadellidae), affects not just cotton and citrus but also Cupressus sempervirens (Mediterranean cypress) [Cupressaceae]. More than a dozen North American trees species are in this family, including
Sequoiadendron giganteum or giant sequoia. Giant sequoia is listed as an endangered species by the IUCN with fewer than 80,000 remaining in its native California.
Chamaecyparis thyoides and C. lawsoniana (Port-Orford cedar). Port-Orford cedar has been decimated in its native range by an introduced pathogen, Phytopthora lateralis. A major breeding effort has developed trees that are resistant to the pathogen; they are now available for people to plant.
Thuja occidentalis, also known as northern white-cedar, eastern white-cedar, or arborvitae,
Taxodium ascendens, also known as pond cypress
several Juniperus
Hesperocyparis macrocarpa also known as Cupressus macrocarpa, or the Monterey cypress. NatureServe ranks the cypress as GI – critically imperiled.
Cotton jassid been reported from several countries in Europe, Africa, and the Middle East.
China has reported the existence of a previously unknown bark beetle species, Phloeosinus metasequoiae (Coleoptera: Curculionidae). It was found infesting Metasequoia glyptostroboides (dawn redwood) trees in China. Affected trees exhibited reddened leaves and holes and tunnels in branches.
China has also discovered a several new hosts utilized by the fungus Pestalotiopsis lushanensis (Sordariomycetes: Amphisphaeriales). Formerly known to infect tea (Camellia sinensis) and several other plant species, P. lushanensis has now been found shoot causing blight and leaf drop on a conifer, deodar cedar (Cedrus deodara) and leaf spots on an angiospermwith congeners in North America — the rare Chinese species, Magnolia decidua. There are eight species of Magnolia native to North America.
Magnolia grandiflora; photo by DavetheMage via Wikimedia
APHIS’ ability to respond to alerts remains uncertain.
The agency’s probationary employees have been fired – just as at other agencies. APHIS staff were prohibited from participating in last week’s annual USDA Invasive Species Research Forum – the 33rd such meeting. The bird flu emergency is demanding all the attention and funds.
So – how can the rest of us fill in?
At the USDA Research Forum I again presented a poster urging greater attention to tree-killing pathogens. Scientists have made considerable progress in identifying factors that indicate whether a non-native insect might pose a significant threat (see blogs on conifer and deciduous species; more to come!). However, USDA had not funded a similar effort to improve understanding of pathogens. The most promising strategy so far are sentinel plantings. However, these systems have weaknesses; I will blog in the near future about another analysis.
I propose that APHIS start by working with independent scientists to determine the actual, current level of pathogens associated with various types of incoming goods. Contact me directly if you wish to read the text of my poster.
Posted by Faith Campbell
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at https://treeimprovement.tennessee.edu/
several Euwallaceae species; E. interjectus is 2nd from the top. Photo from Gomez et al. 2018; ZooKeys 768 19-68
In December 2024, California officials announced detection of a third species of invasive shothole borer beetle in the state. This invasion was found in Santa Cruz County in October 2024. The beetle has been identified as Euwallacea interjectus; the associated fungus is Fusarium floridanum. Like other non-native shothole borers in the same genus already known to be in California, Euwallacea interjectus is native to Southeast Asia.
So far, the infestation extends across at least 75 acres (CDFA proposal). It is affecting primarily box elders (Acer negundo). Other tree species have also been attacked: California sycamore (Platanus racemose), coast live oak (Quercus agrifolia), arroyo willow (Salix lasiolepis), red willow (Salix laevigata), and black cottonwood (Populus balsamifera ssp. trichocarpa). [See the CDFA risk assessment referred to below]. While it is too early to know precisely, E. interjectus is expected to pose a risk of tree dieback in urban, wildland and agricultural landscapes similar to that already caused by its relatives — the Polyphagous shot hole borer (Euwallacea fornicatus s.s. [PSHB]) and Kuroshio shot hole borer (Euwallaceakuroshio [(KSHB)].
The Santa Cruz County Department of Agriculture and University of California Cooperative Extension Service are coordinating with the California Department of Food and Agriculture (CDFA) to monitor and respond to the infestation. Research is being conducted by the University of California to evaluate the full range of potential tree species that may be affected by the beetle.
CDFA is seeking input on whether to designate Euwallacea interjectus as a category “B” pest. Under this category, response to the pest would be carried out by the counties at their own discretion, not by the state. You can advise CDFA’s on this decision until 17 February. Go here.
In its proposal, CDFA notes that several tree hosts of the beetle grow throughout California. The analysis gave a risk ranking of “High (3)” in four categories: climate/host interaction, host range, dispersal and reproduction, and ecosystem-level impacts. The economic risk rank is “Medium (2)” because it might attack only stressed trees – although CDFA concedes that drought stress is common in California. The overall determination is that the consequences of Euwallacea interjectus’ introduction to California is “High (14)”. Still, CDFA proposes to leave response to this introduction up to affected counties.
Santa Cruz County is outside the areas identified by a model developed by Lynch et al. (full citation below) as being at high risk of establishment of the Euwallacea-Fusarium complex, based on analysis of sites where Euwallacea fornicatus and E. kuroshio are already established. Nearby areas are ranked at high risk; these include drier areas in the San Francisco Bay region.
There are at least three four beetles in the Euwallacea fornicatus species complex. Several look almost identical to one another; the only reliable way to tell them apart is by looking at their DNA. However, E. interjectus is substantially larger than E. fornicatus and E. kuroshio, the two already-established shothole borers causing damage in southern California.
Various members of the Euwallacea fornicatus species complex have invaded countries around the world and other parts of the United States. While many of these introductions occurred decades ago – e.g., Hawai`i, Florida, possibly Israel, there appears to have been a spurt of introductions around or after 2000. The PSHB was first detected in California in 2003; the KSHB in 2013. As of 2022, disease caused by these two complexes had spread throughout Orange, San Diego, Los Angeles, Riverside, San Bernardino and Ventura counties. Outbreaks have been detected as far north as Santa Barbara /Santa Clarita. The KSHB had “jumped” to more distant locations in San Luis Obispo and Santa Clara counties. So far, the two later detections apparently do not represent established populations. In November 2023, the PSHB beetle–pathogen complex was confirmed killing hundreds of trees in riparian forests in San Jose, in the San Francisco Bay region. Two host trees – California sycamore and valley oaks – are important in the urban forest canopy of the region
NOTE: the invasive shot hole borers and their associated fungi attacking trees in California are completely unrelated to the laurel wilt complex killing trees in the Lauraceae family in eastern States. This complex involves an ambrosia beetle Xyleborus glabratus and associated fungus Harringtonia (formerly Raffaelea) lauricola.
Lynch, S.C., E. Reyes-Gonzalez, E.L. Bossard, K.S. Alarcon, N.L.R. Love, A.D. Hollander, B.E. Nobua-Behrmann & G.S. Gilbert. 2024. A phylogenetic epidemiology approach to predicting the establishment of multi-host plant pests Communications Biology
Posted by Faith Campbell
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at https://treeimprovement.tennessee.edu/
emerald ash borer; some of PPA grants are funding evaluation of biocontrol efficacy
USDA APHIS has released information about its most recent annual allocation of funds under the Plant Pest and Disease Management & Disaster Prevention Program under §7721 of the Plant Protection Act. (Also see Fading Forests II and III; links provided at the end of this blog.) These funds support both critical needs and opportunities to strengthen the nation’s infrastructure for pest detection, surveillance, identification, and threat mitigation. Since 2009, this USDA program has provided nearly $940 million to more than 5,890 projects.
For FY25 APHIS allocated $62.725 million to fund 339 projects, about 58% of the proposals submitted. About $10 million has reserved for responding to pest and plant health emergencies throughout the year.
According to APHIS’ press release, the highest amount of funds (almost $16 million) is allocated to the category “Enhanced Plant Pest/Disease Survey.” Projects on “Enhanced Mitigation Capabilities” received $13.6 million. “Targetting Domestic Inspection Efforts to Vulnerable Points” received nearly $6 million. “Improving Pest Identification and Detection Technology” was funded at $5 million. Outreach & education received $4 million. I am not sure why these do not total $63 million.
Funding for States and Specific Pests
Wood-boring insects received about $2.3 million. These included more than $869,800 to assess the efficacy of biocontrol for controlling emerald ash borer (EAB) Agrilus planipennis, $687,410 was provided for various detection projects, and $450,000 for outreach efforts related to various pests. Ohio State received $93,000 to optimize traps for the detection of non-native scolytines (bark beetles).
Biocontrol efficacy will also be assessed for hemlock woolly adelgid, invasive shot hole borers, cactus moth, and several invasive plants (including Brazilian pepper). (Contact me to obtain a copy of CISP’s comments on this biocontrol program.)
Opuntia basilaris in Anza Boreggo; one of flat-padded Opuntia vulnerable to the cactus moth; photo by F.T. Campbell
Funding for other pests exceeded $1 million for spotted lanternfly (nearly $1.4 million), Asian defoliators ($1.2 million) and box tree moth (just over $1 million).
$630,000 was provided for detection surveys and studies of the sudden oak death pathogen Phytophthora ramorum, especially how it infects nursery stock. Nursery surveys are funded in Alabama, Louisiana, North Carolina, Ohio, Oklahoma, Pennsylvania, South Carolina, Tennessee, Virginia, and West Virginia. Most of these states are in regions considered most at risk to SOD infection of wildland plants.
sudden oak mortality of tanoak trees in southern Oregon; photo by Oregon Department of Forestry
Oregon received much-deserved $41,000 to evaluate the threat of the NA2 and EU2 lineages of P. ramorum to nurseries and forests Oregon also received $104,000 to respond to the detection of Phytophthora austrocedri in nurseries in the state. The Oregon outbreak has been traced to Ohio, but I see no record of funds to assist that state in determining how it was introduced.
Asian defoliator (e.g., Lymantrid moths) surveys have been funded for several years. This year’s projects are in Alaska, Arkansas, California, Kentucky, Maryland, Massachusetts, Mississippi, Montana, Nevada, North Carolina, Oregon, Tennessee, Texas, Washington, and West Virginia. While I agree that the introduction risk is not limited to coastal states with maritime ports, I don’t what criteria were applied in choosing the non-coastal states which are funded to search for these insects
Spotted lanternfly surveys (including technological improvements) or related outreach are funded in Alabama, Connecticut, Delaware, Kentucky, New Hampshire, New Jersey, North Carolina, Oregon, Pennsylvania, and Tennessee. California’s project is focused on postharvest treatments.
The Don’t Move Firewood project continues to be funded by APHIS. Several states also direct attention specifically to the firewood pathway: Kentucky, Maine, and Michigan.
I applaud the precautionary funding of the Agriculture Research Service to generate of high-quality genomic resources for managing the causal agent of Japanese oak wilt Dryadomyces quercivorous
Florida Department of Agriculture, North Carolina State University, and West Virginia University each received more than $100,000 to improve detection and management of invasive hornets.
Tennessee State University got $100,000 to continue efforts to detect and understand Vascular Streak Dieback in redbud Cercis canadensis.
Posted by Faith Campbell
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at https://treeimprovement.tennessee.edu/
The U.S. Fish and Wildlife Service (USFWS) has taken new action to protect North America’s salamanders from the pathogenic Salamander Chytrid Fungus Batrachochytriumsalamandrivorans; Bsal). The Center for Invasive Species Prevention (CISP) welcomes this action and urges you to help the Service to finalize it.
To read and comment on the interim rule, go here. The comment period closes on March 11.
oriental fire-bellied newt (Cynops orientalis); one of the non-native species imported in largest numbers before the 2016 Lacey Act interim rule; photo by Sebastian Voitel
USFWS acted under its authority to contained in the “injurious wildlife” provisions of the Lacey Act [18 U.S.C. 42(a)]. This statute, first adopted in 1900, empowers the Secretary of Interior to regulate human-mediated transport of any species of wild mammal, wild bird, fish, mollusk, crustacean, amphibian, or reptile found to be injurious to human beings; to the interests of agriculture, horticulture, or forestry; or to America’s wildlife or wildlife resources. Regulated articles include offspring or eggs of the listed species, dead specimens, and animal parts.
Any importation of a listed taxon into the U.S. is regulated. However, regulation of transport within the United States is complicated because of clumsy wording of the statute. In 2017, the D.C. Circuit Court of Appeals [U.S. Association of Reptile Keepers, Inc. v. Zinke [852 F.3d 1131 (D.C. Cir. 2017)] ruled that the law regulates transport of listed species (and their progeny, parts, etc.) between the contiguous 48 States and several other jurisdictions: Hawai`i, Puerto Rico, other U.S. territories, and the District of Columbia. However, transport among the “lower 48” states (e.g., from Virginia to Kentucky) or from the “lower 48” states to Alaska, is not regulated (unless the route to or from Alaska passes through Canada). In past years conservationists asked Congress to amend the law to close this obvious gap in protection, but without success.
It is still illegal to transport listed species across any state borders if the wildlife specimen was either imported to the U.S. or transported between the above-enumerated jurisdictions in violation of any U.S. law. [Lacey Act Amendments of 1981, 16 U.S.C. 3372(a)(1)]
Those wishing to transport a listed species for zoological, educational, medical, or scientific purposes may apply for a permit from USFWS to do so.
The threat to salamanders
The United States is a center of diversity for salamanders. Our nation is home to 221 species of salamanders, more than any other country. These species are in 23 genera in nine families. In fact, nine of the 10 families of salamanders worldwide are found in the U.S. Highest diversity is found along the Pacific Coast and in the southern Appalachian Mountains. As the most abundant vertebrates in their forest habitats, salamanders make significant contributions to nutrient cycling and even carbon sequestration.
Because they depend on both aquatic and terrestrial habitats, salamanders face many threats to their existence. Twenty species of American salamanders from 6 genera (Ambystoma, Batrachoseps, Eurycea, Necturus, Phaeognathus, Plethodon) are listed under the Endangered Species Act link as endangered or threatened. A subspecies of hellbender salamander (Cryptobranchus alleganiensis alleghaniensis) has been proposed for listing.
Amylosterium xxx – marbled salamander; photo by John B. Clare via Flickr
Over the last 12 years, they have faced an alarming new threat.
In 2013, European scientists detected rapid, widespread death of salamander populations in the Netherlands. They determined that the cause was a fungal disease caused by Batrachochytrium salamandrivoran (Bsal). Their alarm was heightened because this fungus is closely related to another, Batrachochytrium dendrobatidis (Bd), which had recently caused serious decline of more than 100 frog and toad species, including driving several to extinction, and had been transported to all continents except Antartica.
Responding to this new threat, amphibian conservation specialists and wildlife groups generally banded together to put pressure on the USFWS to take regulatory action. In response, in 2016, the USFWS adopted an interim rule link prohibiting importation of 20 genera of salamanders. These genera had been shown by scientists to contain at least one species which either suffered mortality when it was exposed to Bsal or could transmit the disease to other salamanders. At the time, Bsal had been shown by scientific studies to be lethal to two American species; USFWS had evidence that U.S. species in other genera could “carry” the pathogen and infect other animals. Three of the species included in the 2016 action had already been listed as endangered or threatened. USFWS’ action cut down the number of salamanders being imported annually by ~95% (based on official import data compiled by the USFWS’ Office of Law Enforcement).
The prohibitions do not apply to articles that cannot transmit the fungus. These include eggs or gametes; parts or tissues that have been chemically preserved, chemically treated, or heat treated so that the pathogen, if present, is rendered non-viable; and molecular specimens consisting of only the nucleic acids from organisms.
Now, 8 years later, the USFWS is acting to finalize the 2016 “interim” rule and to regulate importation and transportation of an additional 16 genera of salamanders. This step had been urged by the National Environmental Coalition on Invasive Species (NECIS), and many others, in their public comments on that Interim Rule. Extending protection to these 16 genera is based on research conducted since the 2016 Rule. Species in 13 of the newly protected genera are considered likely carriers of the disease. Nine species have been demonstrated to be killed by Bsal. No studies have yet determined the vulnerability of more than 50 species in 10 genera of North American salamanders, including four species listed under the Endangered Species Act.
The 36 genera covered by the combined actions of 2016 and 2025 actions are currently considered to comprise ~ 426 species. However, changes in taxonomy are frequent. So USFWS is no longer enumerating the species protected, but is instead relying on listing genera. The regulations apply to all species in a listed genus (whether so classified now or in the future) as well as hybrids of species in any listed genus, including offspring from a pair in which only one of the parents is in a genus listed as injurious.
Appalachian hellbender Cryptobranchus alleganiensis alleghaniensis; historic book illustration via Flickr
USFWS chose to issue “interim” rules in both 2016 and 2025 because that action takes effect almost immediately. (The 2025 interim rule take effect on January 25th.) The usual rulemaking process governed by the Administrative Procedure Act (5 U.S.C. 551 et seq.) often takes years to complete. During that time, the species proposed for listing may still be imported and transported – that is, they could place additional salamander populations at risk of infection by Bsal. The USFWS states that it is unlikely to be able to protect or restore species and ecosystems if the pathogen does become established in the U.S.
In the interval between 2016 and now, Canada banned importation of all living or dead salamanders, eggs, sperm, tissue cultures, and embryos in response to the Bsal threat.
During these years scientists also completed several studies aimed at clarifying which salamander species are either at risk of infection by Bsal or are able to harbor and transmit the pathogen to other salamanders. The USFWS cites studies by, inter alia, Yuan et al. 2018, Carter et al. 2020, Barnhart et al. 2020, Grear et al. 2021, and Gray et al. 2023. USFWS says it cannot act in the absence of such studies, since it must justify its protective actions on scientifically defensible information.
Another relevant question is whether Bsal is already established in North America? Waddle et al. 2020 carried out an intensive search in 35 states that found no evidence that it is. The USFWS concludes that prohibiting importation of additional salamander taxa is still an effective measure to protect North American biodiversity. This is because the international commercial trade in salamanders is the most likely pathway by which Bsal would be introduced to the United States. We note in support of this assertion that former USFWS employee Su Jewell found years ago that none of the 288 non-indigenous species listed as injurious while they are not established in the U.S. has become established since the listing.
The Federal Register document includes a lengthy discussions of why the USFWS has chosen to act under the Lacey Act rather than try some other approach, e.g., setting up quarantine areas or a disease-free certification program for traded salamanders. Among the factors they considered were the current absence of certainty in testing procedures and the possibility of falsified documentation.
WEAKNESSES THE LACEY ACT
The Lacey Act is the principal statute under which the U.S. Government tries to manage invasive species of wildlife – at least those that are not considered “plant pests”. It is not surprising that a law written 125 years ago is no longer the best fit for current conservation needs. See our earlier blog and discussions by, inter alia, Fowler, Lodge, and Hsia and Anderson.
Here, the USFWS lacks authority to regulate pathogens [viruses, bacteria, and fungi that cause disease] or fomites (materials, such as water, that can act as passive carriers and transfer pathogens). Instead, USFWS regulates the hosts. The USFWS previously listed dead salmonids as “injurious” because their carcasses can transmit several viruses.
Another issue is that USFWS cannot designate a taxon “injurious” and regulate trade in it until the Service has conclusive scientific evidence that the species or genus meets the definition. The USFWS has chosen to rely on genus-level data rather than require that each species be tested. Still, as we noted above, American salamanders in 10 genera remain outside the Lacey Act’s protections because studies have not yet been conducted. The USFWS concedes that many of these genera might contain species that are vulnerable to this potentially deadly fungus.
As to relying on laboratory tests of a taxon’s response to the pathogen, the USFWS believes that environmental stresses inherent living in the wild might exacerbate a salamander species’ vulnerability to the disease.
The USFWS is requesting public comment specifically on:
(1) the extent to which species in the 16 genera listed by this interim rule are currently in domestic production for sale – and in which States this occurs? How many businesses sell salamanders from the listed genera between enumerated jurisdictions (e.g., between “lower 48” states and Hawai`i or the District of Columbia)?
(2) What state-listed endangered or threatened species would be affected by introduction of Bsal?
(3) How could this interim rule be modified to reduce costs or burdens for some or all entities, including small entities, while still meeting USFWS’s goals? What are the costs and benefits of the modifications?
(4) Is there any evidence suggesting that Bsal has been established in the U.S.? Or that any of these genera are not carriers of Bsal? Or that additional genera are carriers of Bsal? Is there evidence that eggs or other reproductive material pose a greater risk than USFWS determined, so should be regulated?
(5) Could a reliable health certificate system be developed that would allow imports of Bsal-free salamanders? Are there treatments that would ensure imported salamanders are reliably free of Bsal? How could compliance be monitored? As to salamander specimens, parts, or products, are there other treatments proven adequate to render Bsal non-viable?
(6) Do any Federal, State, or local rules duplicate, overlap, or conflict w/ this interim rule?
CISP encourages those with knowledge of amphibian conservation and disease to comment. Slow progress has been made toward blocking Bsal from the U.S., but the story is not yet closed.
See also the articles by Su Jewell,
Jewell, S.D. 2020 A century of injurious wildlife listing under the Lacey Act: a history. Management of Biological Invasions 11(3): 356–371, https://doi.org/10. 3391/mbi.2020.11.3.01
Jewell, S.D. and P.L. Fuller 2021 The unsung success of injurious wildlife listing under the Lacey Act. Management of Biological Invasions 2021 Volume 12 Issue 3
Posted by Faith Campbell and Peter Jenkins (former member of CISP’s board and consultant to NECIS and other groups on amphibian disease regulation)
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
BLD symptoms; photo by Matt Borden, Bartlett Tree Experts
As beech leaf disease (BLD) is detected in an ever-expanding number of counties from Michigan to Maine south to Virginia, scientists are trying to clarify how the causal nematode — Litylenchus crenatae ssp. mccannii (Lcm) – spreads. One focus is on local spread from tree to tree. Mankanwal Goraya and colleagues set up an experiment in Stone Valley Forest, a recreation and research site managed by Penn State in Huntington County, Pennsylvania. BLD is present – although I have not been able to determine for how many years. [The full citation to Goraya et al. is provided at the end of this blog.]
Goraya et al. (2024) set up four stands, each bearing three funnels, at varying distances from naturally BLD-infected American beech (Fagus grandifolia) trees. Two stands were at 3.51 m from symptomatic trees of starkly different sizes: one of the trees had a dbh of 50 cm, the other of only 5.6 cm. A third close-up stand was set up at 2.20 m from another large tree, having a dbh of 46 cm. The fourth stand was set up at a significantly longer distance, 11.74 m from a symptomatic beech tree; this tree was also small, with a dbh of 5 cm. This arrangement allowed the scientists to detect influences of both distance from the source of infection and relative canopy size of the source tree. They consider dbh to be an adequate substitute for canopy size. There was apparently no other effort to determine or vary the height of “source” trees, although I think that might influence speed of the wind flowing through the canopy.
Goraya et al. also tested whether it is possible to detect the presence of Lcm in association with other invertebrates that live in beech forests. To do this, they counted numbers of nematodes in frass from six species of caterpillars that had been feeding on leaves of infected trees, and in two spider webs spun in the branches of symptomatic trees. They also determined whether these nematodes were alive (active) or inactive – presumably dead.
The study makes clear that Lcm’s life cycle and impact are not as surprising as initially thought. Several species in the family Anguinidae – to which Lcm belongs – are considered significant pests. These nematodes can parasitize aerial parts of the plants (leaves, stems, inflorescences and seeds), causing swellings and galls. Furthermore, they are migratory; they can move across the surface of host tissues using water films. Once they have penetrated the host tissues, they can induce host cell hyperplasia and hypertrophy, resulting in leaf or bulb deformities, shorter internodes, and neoplastic tissues. Furthermore, heavy rainfall and wind are known to play significant roles in the dissemination of plant-infecting nematodes. In their desiccated state on infected seeds, some species of this family can survive passage through animals’ gastrointestinal digestive tract (e.g., domestic livestock, insects, & birds).
A crucial factor is that Lcm can reach densities of thousands of nematodes per leaf by late summer or early fall, increasing the likelihood of their exposure to facilitating environmental conditions at the time they migrate from leaves to buds. And once established within the bud tissues, the nematodes feed on bud scales and newly forming leaves to develop & increase their pop #s. They also use the bud as protection from adverse environmental conditions.
Goraya and colleagues collected samples every other day from September 9 to November 23, 2023 – the period when Lcm migrate from highly infected leaves to newly forming buds. [I note that it in the mid-Atlantic – where Lcm is spreading – we had an extensive drought in autumn 2024 – more than 30 days without any rain from early October into November. I hope scientists are monitoring BLD spread sufficient closely to see whether this drought affected dispersal.]
Nematodes dispersal linked to weather
Goraya and colleagues collected 324 samples from the funnels. Eighty-two percent (n =266) of the samples had nematodes; up to 92% were identified as Lcm. Non-Lcm nematodes were distributed across different genera, mostly classified as free-living nematodes. While several hundred nematodes were found in the funnels on most days, numbers peaked noticeably on some days in September and October. A startling 2,452 nematodes were recovered from a single funnel in October. Depending on the sample, up to 67% of Lcm recovered from the funnels were active.
Analysis of the environmental (weather) variables found that increases in wind speed, humidity, and precipitation (rainfall) coincided with higher numbers of Lcm being recovered from the funnels. However, the effect of wind speed becomes less positive as precipitation increases or vice versa. Goraya et al. suggest a pronounced negative interaction between wind and rain. At low precipitation levels, increased wind speed might facilitate Lcm dispersal. As rainfall increases, higher wind speeds might carry the Lcm nematodes farther away. Support is seen in the fact that fewer nematodes were found in the funnels closer to the BLD-infected trees during these periods. Really heavy rain might push a significant preponderance of nematodes to the ground. The scientists point to a very complex interplay between weather patterns and Lcm population dynamics and dispersal.
BLD symptoms on beech tree in Fairfax County, Virginia – a dozen miles from known infestation; photo by F.T. Campbell
The model did not show any significant influence of maximum temperature on nematode numbers in autumn. Goraya et al. do not speculate on whether temperatures might play a role during summer, as distinct from cooler autumn periods.
Goraya et al.’s findings differ from those of previous studies. Earlier documentation of wind dispersal of nematodes concerned primarily free-living species. It was unexpected to find consistently much higher numbers of Lcm – especially because Lcm is a plant-parasitic nematode. Another surprise is the high proportion of nematodes that are active.
Goraya et al. conclude that because Lcm is actively migrating in large numbers during autumn months, it is primed to take advantage of favorable weather. This nematode will likely survive and thrive in the environmental conditions of beech forests in northeastern North America.
Considering the effect of distance, some findings fit expectations: significantly more Lcm were recovered from funnels placed near symptomatic “source” trees than from those farther away. However, this was not a simple relationship. For example, in two cases the scenarios seemed nearly alike: both “source” trees were large (dbh 46 or 50 cm) and symptoms were “medium-high” (more than half of leaves presenting dark-green interveinal bands). Distance of funnels from the “source” tree differed minimally: 2.2 m versus 3.51 m. Still, the number of nematodes retrieved from the two sets of funnels differed significantly: one set of funnels recovered the highest number of Lcm nematodes obtained during the entire experiment – 2,452; the second contained only up to 600 nematodes. The authors do not offer an explanation.
I am not surprised by the apparently strong correlation between numbers and proximity to the disease source (a symptomatic tree). Nor am I surprised that Lcm nematodes were also found in funnels 11 meters away. I do wonder, however, why they are certain that no source was closer. Detecting early stage infections is notoriously difficult.
beech with large canopy; photo by F.T. Campbell
Goraya et al. also evaluated the effect of size of the source tree. They used dbh a substitute for larger canopies. Trees with larger canopies can host more nematodes, so are likely to contribute more to dispersal events. Two sets of funnels were equidistant from separate “source” trees – 3.51 m. One tree was small – 5.6 cm dbh, 11% as large as the other tree (50 cm). They collected many fewer Lcm nematodes from the smaller tree – the maximum was only 132 compared to 600 (a decrease of 78%).
Still, small trees can apparently support spread of the nematode to a reasonable distance. The fourth set of funnels was set up more than three times farther away (11.74 m) from an infected tree of a similar size (dbh = 5 cm) but recovered almost the same number of Lcm nematodes (0 – 119).
I find it alarming that both small trees in this part of the experiment had low BLD symptoms – only a few leaves were banded. Yet they apparently are the source of Lcm spread. The alternative, as I noted above, is that other “source” trees were in the vicinity but were not detected, possibly because they did not yet display symptoms?
Goraya et al. conclude that “source” tree size directly impacts the number of recovered nematodes. In addition, wind plays a pivotal role in their local distribution. This suggests a complex dispersal pattern in which proximity to the source leads to higher numbers of nematodes but longer-distance spread is possible.
Tussock moth; photo by Jon Yuschock via Bugwood
Nematodes’ association with other organisms
Goraya et al. (2024) collected one each of six caterpillar species from BLD-symptomatic trees. The frass of one – the tussock moth caterpillar (Halysidota tessellaris) — contained 12 nematode specimens — 10 of them Lcm. Two of the Lcm were alive and active. Their presence indicates that Lcm can survive passage through the caterpillar’s gastrointestinal tract. The authors conclude that caterpillars feeding on symptomatic leaves might contribute to local dispersal of Lcm.
Hundreds of Lcm were recovered from the two spider webs collected from the branches of a BLD-infected beech tree. From one web, 255 nematodes were captured; 58 were active. In the second web there were only 34 Lcm, but one-third — 10 – were active.
Goraya et al. (2024) hypothesized that any biotic form having the ability to move from a BLD-infected tree would be able to transport Lcm to other non-infected trees. Beyond caterpillars, they speculate that birds consuming these caterpillars might also disperse Lcm. Doug Tallamy has documented that many birds feed on caterpillars, link although he is focused on those that consume caterpillars in the spring, not the autumn. They note that others are studying that the bird species that feed on beech buds (e.g., finches) might transport nematodes. They note the need for additional research to clarify whether the nematode can survive birds’ digestive system.
Re: detection of live Lcm in spider webs, Goraya et al. suggest two possible interpretations: 1) this finding demonstrates that nematodes might fall from leaves, potentially spreading the infection to other trees beneath the canopy. (Supporting this idea is the fact that sub-canopy trees are often heavily infected with BLD and are frequently the first to exhibit BLD symptoms.) 2) Nematodes in spider webs are very likely to be transported by other “incidental organisms” (e.g., insects, birds, mammals) that feed on invertebrates trapped in webs — thereby potentially increasing the number and impact of nonspecific nematode vectors.
In conclusion, Goraya et al. found that many factors, e.g., distance & size of infected beech trees, wind speed, & humidity, contribute significantly to Lcm dispersal. The multitude of organisms interacting beneath the canopy also play a role.
They suggest that several major questions still need to be explored. These include how Lcm navigate environmental factors in their spread; and whether Lcm can survive – perhaps in a anhydrobioses state –transport over long distances, whether by abiotic or biotic vectors.
I remind my readers of the importance of beech in the hardwood forests in northeastern North America. Many wild animals, including squirrels, wild turkeys, white-tailed deer, and bears depend on beechnuts for fats and proteins. Moreover, some insects birds rely on beech tree canopies for shelter & nesting.
Other Hosts
Beech leaf disease attacks not just American beech (Fagus grandifolia). In North America, it has also attacked planted European beech(F. sylvatica), Chinese beech (F. engleriana), and Oriental beech (F. orientalis). Thus if it spreads it could have severe impacts across forests of much of the Northern Hemisphere.
range of European beech; from Royal Botanic Gardens, Kew
I appreciate that this project was funded by the USDA Forest Service International Program. I will pursue information concerning efforts by USFS Research and Development and the Forest Health Protection program.
SOURCE
Goraya, M., C. Kantor, P. Vieira, D. Martin, M. Kantor. 2024 Deciphering the vectors: Unveiling the local dispersal of Litylenchus crenatae ssp mccanni in the American beech (Fagus grandifolia) forest ecosystem PLOS ONE |https://doi.org/10.1371/journal.pone.0311830 November 8, 2024 1 / 16
Posted by Faith Campbell
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at https://treeimprovement.tennessee.edu/
ʻŌhiʻa trees killed by ROD; photo by Richard Sniezko, USFS
Several Hawaiian tree species are at risk due to introduced forest pests. Two of the Islands’ most widespread species are among the at-risk taxa. Their continuing loss would expose watersheds on which human life and agriculture depend. Habitats for hundreds of other species – many endemic and already endangered – would lose their foundations. These trees also are of the greatest cultural importance to Native Hawaiians.
I am pleased to report that Hawaiian scientists and conservationists are trying to protect and restore them.
Other tree species enjoy less recognition … and efforts to protect them have struggled to obtain support.
1) koa (Acacia koa)
Koa is both a dominant canopy tree and the second-most abundant native tree species in Hawai`i in terms of areas covered. The species is endemic to the Hawaiian archipelago. Koa forests provide habitat for 30 of the islands’ remaining 35 native bird species, many of which are listed under the U.S. Endangered Species Act. Also dependent on koa forests are native plant and invertebrate species and the Islands’ only native terrestrial mammal, the Hawaiian hoary bat. Finally, koa forests protect watersheds, add nitrogen to degraded soils, and store carbon [Inman-Narahari et al.]
Koa forests once ranged from near sea level to above 7000 ft (2100 m) on both the wet and dry sides of all the large Hawaiian Islands. Conversion of forests to livestock grazing and row-crop agriculture has reduced koa’s range. Significant koa forests are now found on four islands – Hawai’i, Maui, O‘ahu, and Kauaʻi. More than 90% of the remaining koa forests occur on Hawai`i Island (the “Big Island) [Inman-Narahari et al.]
In addition to its fundamental environmental role, koa has immense cultural importance. Koa represents strength and the warrior spirit. The wood was used traditionally to make sea-going canoes. Now Koa is widely used for making musical instruments, especially guitars and ukuleles; furniture, surfboards, ornaments, and art [Inman-Narahari et al.]
Koa timber has the highest monetary value of any wood harvested on the Islands. However, supplies of commercial-quality trees are very limited (Dudley et al. 2020). Harvesting is entirely from old-growth forests on private land. [Inman-Narahari et al.]
Koa forests are under threat by a vascular wilt disease caused by Fusarium oxysporum f. sp. koae (FOXY). This disease can kill up to 90% of young trees and – sometimes — mature trees in native forests. The fungus is a soil-dwelling organism that spreads in soil and infects susceptible plants through the root system (Dudley et al. 2020).
Conservation and commercial considerations have converged to prompt efforts to breed koa resistant to FOXY. Conservationists hope to restore native forests on large areas where agriculture has declined. The forestry industry seeks to enhance supplies of the Islands’ most valuable wood. Finally, science indicated that a breeding program would probably be successful. Field trials in the 1990s demonstrated great differences in wilt-disease mortality among seed sources (the proportion of seedlings surviving inoculation ranged from 4% to 91.6%) [Sniezko 2003; Dudley et al. 2009].
In 2003, Dudley and Sniezko outlined a long-term strategy for exploring and utilizing genetic resistance in koa. Since then, a team of scientists and foresters has implemented different phases of the strategy and refined it further (Dudley et al. 2012, 2015, 2017; Sniezko et al. 2016]
First, scientists determined that the wilt disease is established on the four main islands. Having obtained more than 500 isolates of the pathogen from 386 trees sampled at 46 sites, scientists tested more than 700 koa families from 11 ecoregions for resistance against ten of the most highly virulent isolates (Dudley et al. 2020).
The Hawaiian Agricultural Research Center (HARC), supported by public and private partners, has converted the field-testing facilities on Hawai`i, Maui, and Oahu into seed orchards. The best-performing tree families are being grown to maturity to produce seeds for planting. It is essential that the seedlings be not just resistant to FOXY but also adapted to the ecological conditions of the specific site where they are to be planted [Dudley et al. 2020; Inman-Narahari et al. ] Locally adapted, wilt-resistant seed has been planted on Kauaʻi and Hawai`i. Preparations are being made to plant seed on Maui and O‘ahu also. Scientists are also exploring methods to scale up planting in both restoration and commercial forests [R. Hauff pers. comm.].
koa; photo by David Eickhoff via Flickr
Restoration of koa on the approximately half of lands in the species’ former range that are privately owned will require that the trees provide superior timber. Private landowners might also need financial incentives since the rotation time for a koa plantation is thought to be 30-80 years. [Inman-Narahari et al.]
Plantings on both private and public lands will need to be protected from grazing by feral ungulates and encroachment by competing plants. These management actions are intensive, expensive, and must be maintained for years.
Some additional challenges are scientific: uncertainties about appropriate seed zones, efficacy of silvicultural approaches to managing the disease, and whether koa can be managed for sustainable harvests. Human considerations are also important: Hawai`i lacks sufficient professional tree improvement or silvicultural personnel, a functioning seed distribution and banking network — and supporting resources. Finally, some segments of the public oppose ungulate control programs. Inman-Narahari et al.
Finally, scientists must monitor seed orchards and field plantings for any signs of maladaptation to climate change. (Dudley et al. 2020).
2) ʻŌhiʻa Metrosideros polymorpha)
ʻŌhiʻa lehua is the most widespread tree on the Islands. It dominates approximately 80% the biomass of Hawaii’s remaining native forest, in both wet and dry habitats. ʻŌhiʻa illustrates adaptive radiation and appears to be undergoing incipient speciation. The multitude of ecological niches and their isolation on the separate islands has resulted in five recognized species in the genus Metrosideros. Even the species found throughout the state, Metrosideros polymorpha, has eight recognized varieties (Luiz et al. (2023) (some authorities say there are more).
Loss of this iconic species could result in significant changes to the structure, composition, and potentially, the function, of forests on a landscape level. High elevation ‘ohi‘a forests protect watersheds across the state. ʻŌhiʻa forests shelter the Islands’ one native terrestrial mammal (Hawaiian hoary bat), 30 species of forest birds, and more than 500 endemic arthropod species. Many species in all these taxa are endangered or threatened (Luiz et al. 2023). The increased light penetrating interior forests following canopy dieback facilitates invasion by light-loving non-native plant species, of which Hawai`i has dozens. There is perhaps no other species in the United States that supports more endangered taxa or that plays such a geographical dominant ecological keystone role [Luiz et al. 2023]
For many Native Hawaiians, ‘ōhi‘a is a physical manifestation of multiple Hawaiian deities and the subject of many Hawaiian proverbs, chants, and stories; and foundational to the scared practice of many hula. The wood has numerous uses. Flowers, shoots, and aerial roots are used medicinally and for making lei. The importance of the biocultural link between ‘ōhi‘a and the people of Hawai`i is described by Loope and LaRosa (2008) and Luiz et al. (2023).
In 2010 scientists detected rapid mortality affecting ‘ōhi‘a on Hawai‘i Island. Scientists determined that the disease is caused by two recently-described pathogenic fungi, Ceratocystis lukuohia and Ceratocystis huliohia. The two diseases, Ceratocystis wilt and Ceratocystis canker of ʻōhiʻa, are jointly called “rapid ‘ōhi‘a death”, or ROD. The more virulent species, C. lukuohia, has since spread across Hawai`i Island and been detected on Kaua‘i. The less virulent C. huliohia is established on Hawai`i and Kaua‘i and in about a dozen trees on O‘ahu. One tree on Maui was infected; it was destroyed, and no new infection has been detected [M. Hughes pers. comm.] As of 2023, significant mortality has occurred on more than one third of the vulnerable forest on Hawai`i Island, although mortality is patchy.
[ʻŌhiʻa is also facing a separate disease called myrtle rust caused by the fungus Austropuccinia psidii; to date this rust has caused less virulent infections on ‘ōhi‘a.]
rust-killed ‘ōhi‘a in 2016; photo by J.B. Friday
Because of the ecological importance of ‘ōhi‘a and the rapid spread of these lethal diseases, research into possible resistance to the more virulent pathogen, C. lukiohia began fairly quickly, in 2016. Some ‘ōhi‘a survive in forests on the Big Island in the presence of ROD, raising hopes that some trees might possess natural resistance. Scientists are collecting germplasm from these lightly impacted stands near high-mortality stands (Luiz et al. 2023). Five seedlings representing four varieties of M. polymorpha that survived several years’ exposure to the disease are being used to produce rooted cuttings and seeds for further evaluation of these genotypes.
ʻŌhiʻa flowers
Encouraged by these developments, and recognizing the scope of additional work needed, in 2018 stakeholders created a collaborative partnership that includes state, federal, and non-profit agencies and entities, ʻŌhiʻa Disease Resistance Program (‘ODRP) (Luiz et al. 2023). The partnership seeks to provide baseline information on genetic resistance present in all Hawaiian taxa in the genus Metrosideros. It aims further to develop sources of ROD-resistant germplasm for restoration intended to serve several purposes: cultural plantings, landscaping, and ecological restoration. ‘ODRP is pursuing screenings of seedlings and rooted cuttings sampled from native Metrosideros throughout Hawai`i while trying to improve screening and growing methods. Progress will depend on expanding these efforts to include field trials; research into environmental and genetic drivers of susceptibility and resistance; developing remote sensing and molecular methods to rapidly detect ROD-resistant individuals; and support already ongoing Metrosideros conservation. If levels of resistance in wild populations prove to be insufficient, the program will also undertake breeding (Luiz et al. 2023).
To be successful, ‘ODRP must surmount several challenges (Luiz et al. 2022):
increase capacity to screen seedlings from several hundred plants per year to several thousand;
optimize artificial inoculation methodologies;
determine the effects of temperature and season on infection rates and disease progression;
find ways to speed up seedlings’ attaining sufficient size for testing;
develop improved ways to propagate ʻōhiʻa from seed and rooted cuttings;
establish sites for field testing of putatively resistant trees across a wide range of climatic and edaphic conditions;
establish seed orchard, preferably on several islands;
establish systems for seed collection from the wide variety of subspecies/varieties;
if breeding to enhance resistance is appropriate, it will be useful to develop high-throughput phenotyping of the seed orchard plantings.
Developing ROD-resistant ‘ōhi‘a is only one part of a holistic conservation program. Luiz et al. (2023) reiterate the importance of quarantines and education to curtail movement of infected material and countering activities that injure the trees. Fencing to protect these forests from grazing by feral animals can drastically reduce the amount of disease. Finally, scientists must overcome the factors there caused the almost complete lack of natural regeneration of ‘ōhi‘a in lower elevation forests. Most important are competition by invasive plants, predation by feral ungulates, and the presence of other diseases, e.g., Austropuccinia psidii.
Hawaii’s dryland forests are highly endangered: more than 90% of dry forests are already lost due to habitat destruction and the spread of invasive plant and animal species. Two tree species are the focus of species-specific programs aimed at restoring them to remaining dryland forests. However, support for both programs seems precarious and requires stable long-term funding; disease resistance programs often necessitate decades-long endeavors.
naio in bloom; photo by Forrest & Kim Starr via Creative Commons
1) naio (Myoporum sandwicense)
Naio grows on all of the main Hawaiian Islands at elevations ranging from sea level to 3000 m. While it occurs in the full range of forest types from dry to wet, naio is one of two tree species that dominate upland dry forests. The other species is mamane, Sophora chrysophylla. Naio is a key forage tree for two endangered honeycreepers, palila (Loxioides bailleui) and `akiapola`au (Hemignathus munroi). The tree is also an important host of many species of native yellow-face bees (Hylaeus spp). Finally, loss of a native tree species in priority watersheds might lead to invasions by non-native plants that consume more water or increase runoff.
The invasive non-native Myoporum thrips, Klambothrips myopori, was detected on Hawai‘i Island in December 2008 (L. Kaufman website). In 2018 the thrips was found also on Oahu (work plan). The Myoporum thrips feeds on and causes galls on plants’ terminal growth. This can eventually lead to death of the plant.
Aware of thrips-caused death of plants in the Myoporum genus in California, the Hawaii Department of Lands and Natural Resources Division of Forestry and Wildlife and the University of Hawai‘i began efforts to determine the insect’s distribution and infestation rates, as well as the overall health of naio populations on the Big Island. This initiative began in September 2010, nearly two years after the thrips’ detection. Scientists monitored nine protected natural habitats for four years. This monitoring program was supported by the USFS Forest Health Protection program. This program is described by Kaufman.
naio monitoring sites from L. Kaufman article
The monitoring program determined that by 2013, the thrips has spread across most of Hawi`i Island, on its own and aided by human movement of landscaping plants. More than 60% of trees being monitored had died. Infestation and dieback levels had both increased, especially at medium elevation sites. The authors feared that mortality at high elevations would increase in the future. They found no evidence that natural enemies are effective controlling naio thrips populations on Hawai`i Island.
Kaufman was skeptical that biological control would be effective. She suggested, instead, a breeding program, including hybridizing M. sandwicensis with non-Hawaiian Myoporum species that appear to be resistant to thrips. Kaufman also called for additional programs: active monitoring to prevent thrips from establishing on neighboring islands; and collection and storage of naio seeds.
Ten years later, in February 2024, DLNR Division of Forestry and Wildlife adopted a draft work plan for exploring possible resistance to the Myoporum thrips. Early steps include establishing a database to record data needed to track parent trees, associated propagules, and the results of tests. These data are crucial to keeping track of which trees show the most promise. Other actions will aim to hone methods and processes. Among practical questions to be answered are a) whether scientists can grow even-aged stands of naio seedlings; b) identifying the most efficient resistance screening techniques; and c) whether K. myopori thrips are naturally present in sufficient numbers to be used in tests, or – alternatively – whether they must be augmented. [Plan]
Meanwhile, scientists have begun collecting seed from unaffected or lightly affected naio in hotspots where mortality is high. They have focused on the dry and mesic forests of the western side of Hawai`i (“Big”) Island, where the largest number of naio populations still occur and are at high risk. Unfortunately, these “lingering” trees remain vulnerable to other threats, such as browsing by feral ungulates, competition with invasive plants, drought, and reduced fecundity & regeneration.
Hawai`i DLNR has secured initial funding from the Department of Defense’s REPI program to begin a pest resistance project and is seeking a partnership with University of Hawai`i to carry out tests “challenging” different naio families’ resistance to the thrips [R. Hauff pers. comm.]
wiliwili; photo by Forrest & Kim Starr
2) wiliwili (Erythrina sandwicensis)
Efforts to protect the wiliwili have focused on biological control. The introduced Erythrina gall wasp, Quadrastichus erythrinae (EGW) was detected on the islands in 2005. It immediately caused considerable damage to the native tree and cultivated nonnative coral trees.
A parasitic wasp, Eurytoma erythrinae, was approved for release in November 2008 – only 3 ½ years after EGW was detected on O‘ahu. The parasitic wasp quickly suppressed the gall wasp’s impacts to both wiliwili trees and non-native Erythrina. By 2024, managers are once again planting the tree in restoration projects.
However, both the gall wasp and a second insect pest – a bruchid, Specularius impressithorax – can cause loss of more than 75% of the seed crop. This damage means that the tree cannot regenerate. By 2019, Hawaiian authorities began seeking permission to release a second biocontrol gent, Aprostocitus nites.Unfortunately, the Hawai’i Department of Agriculture still has not approved the release permit despite five years having passed. Once they have this approval, the scientists will then need to ask USDA Animal and Plant Health Inspection Service (APHIS) for its approval [R. Hauff, pers. comm.]
SOURCES
www.RapidOhiaDeath.org
Dudley, N., R. James, R. Sniezko, P. Cannon, A. Yeh, T. Jones, & Michael Kaufmann. 2009? Operational Disease Screening Program for Resistance to Wilt in Acacia koa in Hawai`i. Hawai`i Forestry Association Newsletter August 29 2009
Dudley, N., T. Jones, K. Gerber, A.L. Ross-Davis, R.A. Sniezko, P. Cannon & J. Dobbs. 2020. Establishment of a Genetically Diverse, Disease-Resistant Acacia koa Seed Orchard in Kokee, Kauai: Early Growth, Form, & Survival. Forests 2020, 11, 1276; doi:10.3390/f11121276 www.mdpi.com/journal/forests
Friday, J. B., L. Keith, and F. Hughes. 2015. Rapid ʻŌhiʻa Death (Ceratocystis Wilt of ʻŌhiʻa). PD-107, College of Tropical Agriculture and Human Resources, University of Hawai‘i, Honolulu, HI. URL: https://www.ctahr.HI.edu/oc/freepubs/pdf/PD-107.pdf Accessed April 3, 2018.
Friday, J.B. 2018. Rapid ??hi?a Death Symposium -West Hawai`i (“West Side Symposium”) March 3rd 2018, https://vimeo.com/258704469 Accessed April 4, 2018 (see also full video archive at https://vimeo.com/user10051674)
Inman-Narahari, F., R. Hauff, S.S. Mann, I. Sprecher, & L. Hadway. Koa Action Plan: Management & research priorities for Acacia koa forestry in Hawai`i. State of Hawai`i Department of Land & Natural Resources Division of Forestry & Wildlife no date
Kaufman, L.V, J. Yalemar, M.G. Wright. In press. Classical biological control of the erythrina gall wasp, Quadrastichus erythrinae, in Hawaii: Conserving an endangered habitat. Biological Control. Vol. 142, March 2020
Loope, L. and A.M. LaRosa. 2008. ‘Ohi’a Rust (Eucalyptus Rust) (Puccinia psidii Winter) Risk Assessment for Hawai‘i.
Luiz, B.C. 2017. Understanding Ceratocystis. sp A: Growth, morphology, and host resistance. MS thesis, University of Hawai‘i at Hilo.
Luiz, B.C., C.P. Giardina, L.M. Keith, D.F. Jacobs, R.A. Sniezko, M.A. Hughes, J.B. Friday, P. Cannon, R. Hauff, K. Francisco, M.M. Chau, N. Dudley, A. Yeh, G. Asner, R.E. Martin, R. Perroy, B.J. Tucker, A. Evangelista, V. Fernandez, C. Martins-Keli’iho.omalu, K. Santos, R. Ohara. 2023. A framework for establishlishing a rapid ‘Ohi‘a death resistance program New Forests 54, 637–660. https://doi.org/10.1007/s11056-021-09896-5
Sniezko, R.A., N. Dudley, T. Jones, & P. Cannon. 2016. Koa wilt resistance & koa genetics – key to successful restoration & reforestation of koa (Acacia koa). Acacia koa in Hawai‘i: Facing the Future. Proceedings of the 2016 Symposium, Hilo, HI: www.TropHTIRC.org , www.ctahr.HI.edu/forestry
Posted by Faith Campbell
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at https://treeimprovement.tennessee.edu/
