The discovery of the eight-toothed spruce bark beetle in the UK has caused much concern and speculation in recent years, but as the Forestry Commission announces new action to protect against the pest, answers have been offered as to how and where it first arrived.
IPS typographus is here in the United Kingdom. At least 44 breeding populations have been identified since the first findings were made at Ashford in Kent in 2018. Beetle breeding sites now extend across southern England from Kent through East and West Sussex into Surrey. The advanced stage of the first infestation found in 2018 suggested it had been ongoing for a number of years.
So is this spruce bark beetle now established in the UK? I would say yes. Ips has been breeding in the UK for at least five years, maybe 10 or even more. Even if the Forestry Commission (FC) manages to eradicate all 44 (or more) breeding sites, these will be replenished by new ones. That’s because the FC now says the main entry pathway is by ‘blow over’ – adult beetles winging it (with wind assistance) from points in continental Europe at anything from 50 to 500 km from their landing sites in England. This theory is a complete turnaround from the traditionally acclaimed pathway for long-distance travel which is on bark-covered Norway spruce timber and other spruce material.
European scientists have been researching all aspects of Ips, including movement of adult beetles, for hundreds of years. Notable is the huge difference in perception of long-distance travel by Ips among previous European scientists compared with our own today.
The European Plant Protection Organisation (EPPO) data sheet on Ips says: “Roughly 10 per cent of the population flies above the forest canopy and have the possibility of travelling considerable distances with wind, sometimes over tens of kilometres. Beetles have been found in the stomachs of trout in lakes 35 km from the nearest spruce forest, probably carried by the wind.”
Distances not to be sneezed at, but nowhere near the hundreds of kilometres our scientists are now claiming for routine flight of Ips adult beetles. But let’s consider what has been said over recent years this side of the channel.
CONFLICTING REPORTS
A clutch of weighty documents have been published by the UK plant health authorities over the last 10 years, including contingency plans, rapid pest risk analyses and comprehensive research reports.
The first of significance was an FC contingency plan for Ips written by Liz Poulsom, published in October 2015. That document said: “Adult Ips typographus beetles can fly up to 4 km in search of suitable host material, and can also be transported by abiotic factors such as wind. Dispersal over longer distances depends on transportation under the bark of logs. It is one of the most commonly detected pests travelling on solid wood packaging.”
That was followed by a report from Forest Research, ‘The threat to UK conifer forests posed by Ips typographus’, written by Hugh Evans, published in 2021. He said: “Dispersal of beetles tends to be very local, especially at low population densities, with most new attacks occurring within 500 m and frequently less than 100 m of the source. However, long-distance flights of greater than 50 km can also occur, in particular when they are wind-assisted. The transport of beetles in wood and wood products via trade is the main pathway for long-distance dispersal.”
This clearly alluded to longer-distance travel, albeit at the lower end of what is now being claimed, while adhering to bark-covered timber and wood as the main pathway for long-distance travel.
Everything abruptly changed when a rapid pest risk analysis conducted by Forest Research scientists (Daegan Inward, Joan Webber, Max Blake, Sarah Facey, Hugh Evans) was published in April 2023. It said: “New evidence indicates that adult Ips typographus are capable of dispersing naturally across the English Channel from continental Europe; this is considered to be the pathway by which multiple localised incursions of the pest were initiated in SE England in 2021.
“Very large populations of I. typographus have built up across western and central Europe in recent years, including unprecedented population peaks in Belgium and France.”
BEHIND THE SCENES AT THE FC
This new view was confirmed in October 2023 in an account posted by Fred Toft, biosecurity officer at the FC – ‘Behind the Scenes at the Forestry Commission: Managing Ips typographus ... five years on’. He said: “Although it had always been previously thought that the most likely pathway for the beetle to reach the UK was via imported wood or wood packaging, a new hypothesis that the beetle was naturally dispersing across the channel was suggested after the first insect traps in 2019 caught Ips typographus, but ground surveys in 2019 and 2020 failed to find any evidence of breeding populations in the UK. A DEFRA-funded study testing this hypothesis was conducted by scientists at Forest Research and the Université Libre de Bruxelles, and its results supported the hypothesis of natural dispersal across the channel.”
I have always been sceptical about Ips beetles winging it all the way from Europe, for a range of reasons. Even if I accept that it is possible for beetles to make it across the English Channel, I can’t accept all 44 (or more) infestations identified started this way. My scepticism was further fuelled because UK plant health authorities had been reticent about revealing the nature of the evidence they said they had for the ‘blow over’ view.
ALL IS REVEALED – OR IS IT?
So where was this hard evidence for ‘blow over’? It did exist, but had been sat on for at least a year awaiting publication in a research-based journal. I know only too well from my own experience that researchers need to be careful about how much they give away before publication, lest their ideas and findings are pinched by others.
The research and its findings were duly published on 14 March 2024, in Journal of Pest Science, though the paper had been received by the journal on 18 August 2023. Titled ‘Evidence of cross-channel dispersal into England of the forest pest Ips typographus’, its summary stated: “By trapping beetles simultaneously on both sides of the channel, coincident with suitable weather conditions and a large-scale dispersal event in June 2021 centred on the Ardennes region, we may be confident that dispersal has occurred across the channel. Simultaneous detections of I. typographus were also made at this time across southeast England by the monitoring programme.”
Since June 2021, at least 27 individual incursions of I. typographus have been detected in Kent, Sussex and Surrey as small and isolated populations exhibiting one or more breeding galleries on Norway spruce trees (typically windthrown or snapped tops). Based on the extent and age of gallery formation, all incursions were concluded to have been initiated during the same June 2021 dispersal period.
Eradication measures have been applied to each incursion detected, requiring considerable resources. It is noteworthy that only five days were assessed as suitable for dispersal during that critical period and that a longer window of opportunity might have led to even more localised establishments.
The coup de grace came when I found another relevant research article on the web, produced by the full weight of the UK plant health authorities. It covered in detail the first finding of a breeding population – now six years ago – and subsequent findings and action taken from 2019 to 2021. It is written by an assemblage of authors drawn from Forest Research, the FC and DEFRA, and numbering 14 people, which must be some kind of record.
The title of the article is ‘Recent outbreaks of the spruce bark beetle Ips typographus in the UK: Discovery, management, and implications’, published in Trees, Forests and People.
This is a summary of what the 14 authors had to say:
“Ips typographus is not native to the UK and before 2018 it had not been found established anywhere within the country. In November 2018, however, several adult Ips typographus were found in a billet trap set up as part of annual surveys that the UK carries out to monitor for this and other quarantine bark beetle pests.
"The finding of adult beetles in the billet trap, a few miles south of Ashford in Kent, led to the discovery of a breeding population in an adjacent woodland.
“Delimiting surveys to 1 km and further surveys to 50 km showed that the infestation was confined to a single stand of Norway spruce. The stand was felled in January and February 2019, and the material destroyed, and beetles emerging on the site were trapped out using pheromone traps, billet piles and trap trees.
"These prompt actions eradicated the breeding population, but small numbers of adult Ips typographus continued to be caught on the outbreak site in 2020 and 2021.
“These captures, and numerous adult Ips typographus caught in pheromone traps set up across the region in response to the outbreak, indicate that incursions of adult Ips typographus are occurring on a regular basis, most likely from source populations in northern France and Belgium. The arrival of adult Ips typographus over a wide area and the potential for further outbreaks represents a continuing threat to spruce woodlands in south-east England.”
BACK TO THE SOURCE
The identity of the woodlands where this first breeding population was found in November 2018 has now been publicised. The main infestation occurred in a stand of Norway spruce located 200 m east of the permanent quarantine pest survey plot, in a mixed broadleaf and conifer woodland called Packing Wood. A small pocket of infestation was also found in the same wood (Haberdasher’s Wood) as the quarantine pest survey plot. These two woodlands are located 6.5 km south of Ashford in Kent. Packing Wood is owned by the Woodland Trust and Haberdasher’s Wood is managed by the FC as part of the public forest estate.
The real shocker is the distribution and number of beetles identified across south, south-east and eastern England between 2018 and 2021. We knew breeding populations had been identified in Kent, East and West Sussex and Surrey, but not that adult beetles had also been found in pheromone traps located in other counties, or the sheer numbers involved. The situation appeared to be worsening with by far the biggest number caught over the widest distribution in the year 2021. That was a total of 7,404 adult beetles caught in pheromone traps located in Kent, East Sussex, Surrey, Hampshire, Berkshire, Buckinghamshire, Essex and Suffolk. Some trap catches were as high as 820 beetles.
The evidence for and extent of ‘blow over’ of beetles from continental Europe looks convincing, but by the same token presents a no-win situation for UK forestry unless the UK plant health authorities fell and burn every last Norway spruce (and Serbian spruce) on the landscape. Even then, the beetle may still round on Sitka spruce*.
Despite convincing evidence, the sceptic in me still wants some questions answered. As expected, the pest explosion in Europe from which these migratory beetles are claimed to have originated was way over to the east in the Ardennes region of southern Belgium, which means beetles had managed to make it 500 km across France, the English Channel and into southern England, a distance way beyond anything claimed in decades of studies into this aspect of Ips behaviour.
The continental European pest explosion – which is said to have caused this dispersal of insects to England – occurred in 2021, so anything prior to this cannot be attributed to this event. Some way of ‘tagging’ beetles would put these robust-looking research findings beyond doubt.
I would still be wary about assigning each of these 44 (or more) outbreaks to airborne beetles flying 500 km to reach southern England. I believe the import of infested Norway spruce earmarked for biomass burning and firewood is underplayed. Landowners and foresters should take note of a proclamation at the very end of the joint Belgium/UK scientific paper. It reads: “The severity and scale of I. typographus outbreaks across central Europe provide a worrying backdrop to the detections of the beetle in Britain, so that a shift away from planting and growing spruce in southern England is now being considered”.
An effective ban on growing Norway spruce could rapidly extend to other parts of England and even Wales. If a beetle can make the 500 km from the Ardennes in southern Belgium to Surrey in England, what’s an extra 180 km from Guildford to Abergavenny?
With breeding populations still confined to the counties of Kent, East and West Sussex and Surrey south of the River Thames, landowners and foresters with spruce plantations in northern England and Scotland could still feel relatively safe. That was until May of 2024, when the FC announced an outbreak of Ips had been found in East Anglia, though the county was not specified. This meant it could be in Essex, Suffolk, Norfolk, Northamptonshire, Cambridgeshire or even Lincolnshire.
Be that as it may, the FC soon announced an extension of the demarcated area to cover the remainder of Essex, extra parts of Hertfordshire, eastern parts of Bedfordshire and Cambridgeshire, the whole of Suffolk and Norfolk and the southernmost part of Lincolnshire.
This effectively extended the demarcated area an extra 100 miles northwards and nearer to the swathes of Sitka spruce which are the very foundations of modern commercial forestry in the UK. Given how the demarcated area has been extended, I will stick my neck out and say the new outbreak is in the area of mid Suffolk/mid Norfolk, where the two counties meet, close to if not in Thetford Forest.
*Ips has since been found on Sitka spruce for the first time in the UK
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