In 2017 I blogged about a study by Hanno Seebens and 44 coauthors that showed that the rate of new introductions of alien species has risen rapidly since about 1800 – and showed no sign of slowing down (a reference to the full article is at the end of this blog). Here’s a brief recap, followed by a 2020 update by Seebens and colleagues.
In 2017, Seebens et al. analyzed a database covering 45,813 first records of 16,926 alien species established in 282 distinct geographic regions. The year with the highest number of reported new detections was 1996 – 585, or an average of more than 1.5 sightings per day.
The authors found that the adoption of national and international biosecurity measures during the 20th Century had slowed introductions – but not sufficiently. Numbers of reported new introductions of fish and mammals had decreased since the early 1950s. However, first recorded introductions of vascular plant species remained high, and introductions of birds and reptiles also continued to rise, largely as pets in countries with strengthening economies.
For taxa introduced primarily accidentally on transport vectors or as contaminants of commodities (e.g., algae, insects, crustaceans, molluscs and other invertebrates), they found a strong correlation between their spread and the market value of goods imported into the region of interest – existing biosecurity regimes had not slowed down the accumulation of these alien taxa.
As a consequence, the authors expected that the numbers of new alien species would continue to increase.
As you are aware, since 2015 I have posted 15 blogs about the continued detections of tree pests in wood packaging, which remains one of the major pathways despite the international regulation ISPM#15. I have found it harder to track insect and pathogen introductions on imported plants, but it surely continues apace.
2020 Study Projects Continuing Rise in Introductions, Especially Arthropods
Hanno Seebens and a smaller set of coauthors (see full reference at the end of this blog) have now produced an estimate of probable introduction rates in the future. They looked at taxon–continent combinations for seven major taxonomic groups and eight continents (excluding Antarctica).
They found an overall increase in established alien species between 2005 and 2050 of 36%.
The study predicted that by the mid-21st Century, there will be distinct increases in alien species numbers, particularly for Europe, but also for Temperate Asia and North America, and for invertebrates in all regions. Europe ranked highest in absolute numbers of new alien species (~2,543; a 64% increase). Temperate Asia was projected to receive about 1,597 species (a 50% increase); North America about 1,484 (a 23% increase); South America about 1,391 (a 49% increase); and the Pacific Islands about 132. Only Australasia could expect a slower rise in introductions. The predicted trajectories of alien species numbers were surprisingly similar for mainland and island regions across taxonomic groups.
Invertebrates showed the highest relative increases. Rates of new detections of alien species were projected to accelerate for arthropods other than crustaceans worldwide, especially for North America (!). The study also projected higher relative increases for aquatic vascular plants and terrestrial insects
All drivers of introduction and invasion are predicted to intensify in the future. This is despite adoption of increasing numbers of countermeasures in recent decades. Most countries’ capacity to proactively counter the rising tide of invasive species is still poor. Furthermore, the principal drivers – intensification of trade and transport, land-use change, and access to new source pools – is expected to continue operating as now – “business as usual”.
spotted lanternfly Holly Ragusa, Pennsylvania Department of Agriculture
Current Status of “New” Detections
Seebens et al. (2020) relied on the Alien Species First Records Database for first detection records up to 2005. More than half (54%) of the first-detection records in the database are vascular plants. Arthropods other than crustaceans made up 28% of the total, birds 6%, fishes 4%, mammals 3%, molluscs 2%, and crustaceans 2%. The 2020 study confirmed the earlier finding that the observed first-record rates of mammals changed at around 1950 from an increasing to a decreasing trend. Finally, the total numbers of non-native species in the Database is much lower in aquatic habitats. (The authors do not discuss whether this reflects actual introductions or gaps in reporting.)
In the database, Europe recorded 38% of all first records, North America 16%, Australasia 15%, South America 9%, Temperate Asia 9%, Africa 6%, Pacific Islands 5% and Tropical Asia 2%.
A comparison to the immediate past (1960-2005) showed that the rates of emerging non-native species were projected to accelerate during 2005-2050, especially for arthropods. As I noted above, North America is predicted to have high increases in absolute numbers. Increases are also predicted for birds. Declines are predicted for mammals and fishes.
Asian giant hornet; photo from University of Florida Department of Entomology
Projected increases for Australasia were consistently lower than in the past.
Caveats:
1) The authors assumed that past patterns of alien species accumulation will continue in the future. They did not attempt to predict efforts to strengthen biosecurity regulations and mitigation strategies.
2) Projections were calculated in the absence of data on many underlying drivers for the historic periods and some taxonomic groups. However, observed trends of newly-detected alien species numbers during the 20th century were surprisingly stable despite distinct political and socio-economic changes.
Seebens and colleagues conclude that implementation of targeted biosecurity efforts can reduce the numbers of new alien species becoming established. However, a significant decrease in rates of alien species numbers on a large scale can only be achieved by a coordinated effort that crosses political borders.
Seebens, H., S. Bacher, T.M. Blackburn, C. Capinha, W. Dawson, S. Dullinger, P. Genovesi, P.E. Hulme, M. van Kleunen, I. Kühn, J.M. Jeschke, B. Lenzner, A.M. Liebhold, Z. Pattison, J. Perg, P. Pyšek, M. Winter, F. Essl. 2020. Projecting the continental accumulation of alien species through to 2050. Global Change Biology. 2020;00:1 -13 https://onlinelibrary.wiley.com/doi/10.1111/gcb.15333
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 http://treeimprovement.utk.edu/FadingForests.htm
dead ash along Accotink Creek, Fairfax County, Virginia photo by F.T. Campbell
As we all know, the emerald ash borer (EAB) has killed millions of ash trees in its invaded range across eastern North America. However, field studies have detected robust regeneration of ash seedlings and saplings in various invaded areas. Ward et al. 2021 (full citation at end of blog) set out to determine whether this regeneration will result in recovery of mature ashes that can perform their ecological role. They conclude that it will not. Instead, they say, the EAB invasion will probably alter successional patterns and composition of large areas of naturally regenerating forests, causing a cascade of ecological impacts in ash-containing ecosystems
Ward and colleagues used USDA Forest Service Forest Inventory and Analysis (FIA data) to quantify ash recruitment and regeneration across the entire eastern United States. Theirs is the first study to evaluate trends across the region, rather than specific locations or stands. They related the FIA recruitment data to EAB spread, as measured by USDA Animal and Plant Health Inspection Service’ (APHIS) record of the first EAB detection in each county.
FIA inventories in 2002-2007 and 2013-2018 show large numbers of ash seedlings and saplings in counties invaded in the first wave of invasion, 2002–2006. These areas had higher densities of both seedlings and saplings than plots in other counties. The earliest-invaded counties were in areas that had extraordinarily high densities of ash before the EAB invasion, so the numbers of seedlings and saplings probably reflected that abundant seed source.
However, by the 2013-2018 inventory ash trees in the smallest overstory class (12.7 cm dbh) were dying at faster rates than they were recruited from seedlings or saplings in all 362 counties recorded by APHIS as EAB-infested before 2013. Ward and colleagues found these negative population trajectories on plots that have been invaded for more than about 10 years. This trend suggests that ash will continue to decline in abundance and may become functionally extinct across the invaded range.
Some U.S. Forest Service biologists are more optimistic about ash recovery in response to biocontrol of the EAB. See their podcast here.
In the risk of functional extinction, ash trees are unfortunately not unique. The authors note similar impacts from the invasion of the hemlock woolly adelgid and beech bark disease.
Data Reveal History of Invasion (spread)
Ward and colleagues focused on the risk of mortality for young ashes as they developed from seedlings to saplings, and, eventually, to overstory trees. The youngest “overstory” trees are 12.7 to 17 cm dbh. FIA data show that even the largest trees in this class are 3 cm smaller than trees that produce seeds.
Mortality was initially uniformly low – less than 2.1% — as measured by the first FIA inventory (2002–2007). This is not surprising because EAB was detected only in 2002, and then in only few counties. (EAB had probably been present for a decade before it was detected.)
By the 2013-2018 FIA inventory, mortality had quadrupled to 8–11% in counties invaded during the 2002–2006 period. In the counties invaded during the 2007–2012 period, morality also rose to 3-5%. Both measurements included all diameter classes. Annual mortality rates in the FIA 2013-2018 inventory were still highest for the counties invaded during 2002–2006 except for the largest trees (those greater than 40 cm dbh). By the time of the 2013-2018 FIA survey, overstory ash densities near the epicenter had since declined substantially. They had been nearly eliminated in some counties in southeastern Michigan. There were still sufficient numbers of smaller trees in the region to exhibit an elevated mortality rate – more than 10% per year in several counties in Michigan, Indian, and Ohio. By contrast, in the most recently invaded areas – those counties recorded by APHIS as infested after 2013 – there was very little change in ash densities compared to the 2002-2007 period. This is hardly surprising since it takes years for mortality to reach levels observable by the FIA process.
dead ash on edge of Pohick Bay, Fairfax County, Virginia photo by F.T. Campbell
Considering trees just entering the overstory category (those with diameters of 12.7 cm dbh), annual mortality increased substantially across the region. Between the first FIA inventory (conducted in 2002-2007) and the second inventory (conducted in 2013-2018), their average annual mortality rose more than four-fold, from 0.08 trees per ha to 0.37 trees per ha. By 2013-2018, recruitment in the 2002–2006 invasion cohort was about 50% less than tree mortality levels; recruitment and mortality were about equivalent for the counties invaded in the 2007–2012 period. Recruitment was [still] significantly higher than mortality for the counties recorded as invaded in 2013–2018. However, Ward and colleagues expect mortality rates of this cohort to accelerate over the next five to 10 years – even in areas with lower ash densities.
Ward and colleagues note that many of the young ash trees were dying before they could reach reproductive age – which they estimated to be about 20 years with a dbh of about 20 cm.
As the invasion progresses and hosts are depleted, mortality rates could slow, but, for ash to persist, it is critical that sufficient numbers of trees reach reproductive age before succumbing to residual EAB populations.
Other factors that might influence ash include competition with trees in other genera. The biocontrol agents now becoming established in young ash forests might increase the likelihood of ash persistence. Still, seed production and seedling survival will need to be frequent and widespread if they are to offset expected mortality. Resilience might also vary depending on individual species’ vulnerability to changes in the climate and to EAB (green and black ash are more vulnerable than white ash).
SOURCE
Ward, S.F., A.M. Liebhold, R.S. Morin, S. Fei. 2021. Population dynamics of ash across the eastern USA following invasion by emerald ash borer. Forest Ecology and Management 479 (2021) 118574
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 http://treeimprovement.utk.edu/FadingForests.htm
Asian giant hornet; photo from University of Florida Department of Entomology
Asian giant hornet (AGH) (Vespa mandarinia) is the world’s largest hornet, reaching sizes of 1.5 – 2 inches long. Its native range includes much of Asia. While media attention has focused on the hornet’s frightening size, the real threat is to honey bees (Apis spp.) and – especially – to the many important crops that bees pollinate.
Over the past year or so, several detections of the Asian giant hornet have been found in the Pacific Northwest – in British Columbia and Washington State. Four of the sites are within a few miles of each other. Two others are separated by miles of open water from the mainland sites. As of mid-October, 18 hornets had been detected in Washington State.
USDA’s Animal and Plant Health Inspection Service (APHIS) has partnered with the Washington Department of Agriculture to try to eradicate the hornet – which will not be easy! However, the Canadian Food Inspection Service (CFIA) has decided not to designate the hornet as a quarantine pest. This decision seems to threaten divergent approaches to the bioinvader. Fortunately, the Province of British Columbia is trying to eradicate its populations – so perhaps the diverging federal approaches will not result in facilitating the hornet’s establishment and spread.
Where the Hornet Is Known to Be
The first detected outbreak of the Asian giant hornet was in Nanaimo, British Columbia – on Vancouver Island. A single hornet was detected in August 2019. [A Canadian commenter said in March 2021 that this turned out to be a different species, V. soror.] A nest was detected in September and destroyed by local beekeepers and BC government officials. However, another hornet was found on the mainland – in White Rock, B.C. – in November 2019 [CFIA Decision Document]. In 2020, there have been several unconfirmed sightings in the Cowichan Valley on Vancouver Island (van Westendorp, pers. comm.).
Meanwhile, beekeepers discovered two AGH outbreaks in Whatcom County, WA, on the U.S. side of the border. These discoveries were in December 2019 and May 2020. There were other, unconfirmed reports in both Washington and British Columbia. [USDA APHIS Environmental Assessment (EA)] Indeed, later in 2020, Washington reported a few more sightings — in the Birch Bay area, just south of Blaine and at a site about eight miles east of Blaine (van Westendorp, pers. comm.)
Three of the hornets found in spring 2020 were mated queens (Zhu et al. 2020), which means at least one colony successfully reproduced last year. One of the mated queens was the second detection in Whatcom County – in Custer, Washington. One article said that the locations of this spring’s queens meant either that the new queens travelled up to 35 kilometres (about 22 miles) before founding their nests or that they came from more than one colony. Either way, it probably means that giant hornets could spread faster than initially thought.
White Rock, BC and Blaine, Washington are a few miles apart on the Canada-U.S. border. Langley is 12 miles to the northeast of White Rock – in the Fraser Valley. Custer is 7 miles southeast of Blaine. Birch Bay is 5 miles south of Blaine. The most recent detection is 8 miles east of Blaine. So all these detections are in close proximity and might represent spread from a single introduction site – or maybe not!
Nanaimo and the Cowichan Valley are on Vancouver Island, which is separated from the other locations by a significant distance and open water. The two island sites are about 30 miles apart. They surely represent one or more separate introductions.
One study found that a single hornet collected from Blaine, Washington differed genetically from a single hornet collected at Nanaimo on Vancouver Island. This suggests separate introductions. However, too little is known about the hornet’s genetic variability across Asia to allow conclusions about possibly separate origins (van Westendorp, pers. comm.; Wilson et al. 2020).
Areas at Risk
The area at risk is potentially much broader than the Pacific Northwest. APHIS’ initial analyses, based on plant hardiness zones, indicated that the hornet could thrive in virtually all the lower 48 states. APHIS’s Environmental Assessment did not address vulnerable areas in Canada or – apparently – in Hawai`i.
Zhu et al. (2020) carried out an assessment of areas most at risk and the hornet’s potential rate of spread. They found that areas with warm to cool annual mean temperature, high precipitation, and high human activity were most likely to be suitable for the hornet. Areas meeting these criteria are found across western and eastern North America, Europe, northwestern and southeastern South America, central Africa, eastern Australia, and New Zealand. Most of central North America and California are less suitable.
Spread could be rapid in the Pacific Northwest: they predicted that the hornet could reach Oregon in 10 years, eastern Washington and British Columbia within 20 years. This prediction is based in part by experience with the invasive congener V. velutina in Europe; it has expanded by 78 km/year in France, 18 km/year in Italy.
Oregon is relying on beekeepers to detect the hornet, which they expect will arrive even earlier than 10 years from now. The Oregon Department of Agriculture has suffered severe budget cuts because of the Covid-19 crash in state tax collections, so the program is trying to save money. As of the beginning of October, none of the hundreds of citizen reports has been a Vespa of any species (J. Vlach, Oregon Department of Agriculture, pers. comm).
Pathways of Introduction
It is not known how the hornet reached North America. Reports from other countries indicate that they can hitchhike in shipments of empty plant containers, or in the straw in which the containers are packed. In addition, some Asian cultures regard the hornets as delicacies, so deliberate importation is possible. Both APHIS and the Canadian Food Inspection Agency (CFIA) have intercepted such shipments (CFIA Decision document; USDA APHIS PPQ New Pest Response).
The Threat
The AGH typically feeds on a variety of terrestrial invertebrates including beetles, mantids, caterpillars, and spiders (EA). During the spring and summer, hornets attack their prey singly. However, in the Aautumn, hornet workers carry out mass attacks against other social Hymenoptera – including other species of Vespa, yellowjackets (Vespula spp.), various paper wasps (Polistes spp.), and honey bees (Apis spp.). Commercial honeybee colonies are typically lost when attacked en masse. They are especially vulnerable because they are more concentrated than wild bee colonies. [EA]
Commercial honeybee colonies pollinate a wide variety of crops, including tree fruits, cane fruits (berries), tree nuts, tomatoes, and even potatoes. Supplies of beef and milk might also be at risk because alfalfa hay is pollinated by bees. Of course, honey production would also be threatened. As USDA APHIS has stated, if the Asian giant hornet spreads it would become a new stress on top of the multiple existing causes of honeybee decline.
Also, there is a direct threat to people. The AGH has a painful sting that can result in anaphylaxis, cardiac arrest, and other complications in susceptible people. Officials emphasize that most people will not be at risk of stings. However, beekeepers are – their usual Personal Protective Equipment (PPE) is not adequate to ward off the hornet’s sting [APHIS EA & New Pest .
APHIS’ programmatic Environmental Assessment notes that the hornet might also pose a threat to vertebrates that nest in ground burrows and decayed trunks and roots near the ground. Burrows chosen by female hornets for nest construction can be surprisingly large, up to 60 cm (24 inches) in diameter. The EA notes that, in Washington State, badgers, marmots, ground squirrels, and other small mammals use dens or burrows. Among these, four pocket gophers and the American wolverine are federally listed under the Endangered Species Act in Washington State. [For a list, see the environmental assessment.] The EA does not discuss whether cavity-nesting birds might also be affected – although the hornets do prefer hollows near or at ground level. The authors of the EA expect vertebrates to abandon any burrows used by the hornet, so they would be displaced rather than harmed by pesticides applied by the program described below.
APHIS program
APHIS and the Washington State Department of Agriculture (WSDA) have begun an eradication program. I think eradication will be challenging because it will be very difficult both to find nests and to destroy them.
Hornets nest typically in forested areas or urban green spaces. There are lots of suitable places in the Pacific Northwest! These wooded areas are interspersed with farms, orchards, and settlements that will provide vulnerable insects as food sources.
Nest destruction involves excavating a hole two meters by two meters. This digging must be in woodlands, often right next to trees.
The key to successful eradication is finding and destroying the nests before they produce reproductive females and males – in autumn. Nest detection will be carried out as follows [EA]:
Starting in April, the agencies bottle traps in trees near the 2019 detection points. The traps are baited with a solution of rice cooking wine and orange juice to attract the worker bees. (The rice wine is added to discourage honeybees from visiting the trap.) Traps catches help define areas where nests are located.
WSDA successfully tracked radio-tagged workers to a nest in mid-October. That nest was in a tree hollow, not underground.
WSDA scientists think there were approximately 200 queens in that single nest. Two were vacuumed out during the initial extraction. Inside the nest they found 76 emergent queens and 108 capped cells with pupae that they believe were also queens. Three more queens were trapped in a bucket of water. This nest had approximately 776 cells; large nests can have up to 4,000. WSDA believes there are other nests in the area; they continue to search.
APHIS’ original plan to use pesticides to kill hornets in the nest has been dropped. Washington plans now to use vacuum extraction followed by introduction of CO2 and excavation of the nest. Washington has also not decided whether to deploy traps with the pesticide fipronil (S. Spichiger, pers. comm.)
WSDA has also asked members of the public to set out homemade hornet traps, and to report any suspicious sightings.
Canada Takes Opposite Tack
The Canadian Food Inspection Agency (CFIA) announced in February 2020 (CFIA Decision Document) that it will not attempt to regulate the Asian giant hornet as a quarantine pest for Canada. Therefore, CFIA will place no restrictions on the import or movement of any commodities that may harbor the Asian giant hornet. CFIA will, however, require permits for deliberate importation of the hornets.
CFIA’s reasoning appears to focus on two factors:
The hornet is an indirect threat to plant health (since AGH attacks pollinators. CFIA has traditionally regulated quarantine pests based primarily on significant direct threats to plant health.
Under the international phytosanitary system, countries that designate an organism to be a quarantine pest must put in place the necessary measures to prevent its entry into the country, as well as officially control the pest when present. CFIA states that “High uncertainties about the pathways of entry puts into question the ability to manage this risk, and ultimately the ability and feasibility of regulating V. mandarinia as a quarantine pest.”
Neither APHIS nor CFIA has authority to regulate threats to human health.
Detection and Eradication Efforts in British Columbia (information from van Westendorp, British Columbia Ministry of Agriculture)
In 2020, British Columbia has focused on detection surveillance. Target areas include vicinity of Nanaimo on Vancouver Island; Fraser Valley from White Rock in the West to Langley/Aldergrove in the East (along the US border); and after several credible (but non-verified) sightings, the Cowichan Valley on Vancouver Island. Because of resource limits, the surveillance effort has sought to engage local governments, border agencies, First Nations, forestry & mining companies, farmers, and beekeepers. The ministry also placed numerous bottle traps and encouraged 170 beekeepers in the Fraser Valley to install and monitor traps in their apiaries.
So far, only one AGH specimen has been sighted or collected in the three British Columbia survey areas during 2020 – the single specimen at Langley detected in May. However, the several detections along the U.S. side of the border (see above on recent detections) has spurred BC officials to intensify survey efforts in the Fraser Valley (van Westendorp). A specimen was collected adjacent to the US border in mid-October just north of the multiple detections in the US, and South of the Langley detection last spring (S. Spicher, pers. comm.).
British Columbia will continue to monitor well into the fall season and resume our surveillance in 2021 and 2022 (van Westendorp).
Hornets are clearly able to be transported and introduced. Vespa ducalis was detected in Vancouver, BC in 2019 and in Texas in 2020. Vespa velutina has become established in Europe (J. Vlach, Oregon Department of Agriculture, pers. comm).
USDA APHIS Asian Giant Hornet Control Program in Washington State Final Environmental Assessment—July 2020
USDA AHIS PPQ New Pest Response
van Westendorp, Paul. British Columbia Ministry of Agriculture, pers. comm.
Wilson, T.M., J. Takahashi, S-Erik Spichiger, I. Kim, and P. van Westendorp. 2020. First Reports of Vespa mandarinia (Hymenoptera: Vespidae) in North America Represent Two Separate Maternal Lineages in WA State, US, and BC, Canada. Annals of the Entomological Society of America · October 2020
Zhu, G., J. Gutierrez Illan, C. Looney, and D.W. Crowder. 2020. Assessing the ecological niche and invasion potential of the Asian giant hornet. PNAS Latest Articles ECOLOGY
