A new study on Ips typographus, the bark beetle which has caused widespread devastation to European forestry in recent years, has outlined its risk to the Sitka spruce.
‘Investigating the threat to Sitka spruce from Ips typographus: discrimination and colonization of Britain’s principal commercial conifer by a damaging forest pest’ was published by Forest Research and Rothamsted Research, in the Pest Management Science journal.
Ips typographus, commonly known as the eight-toothed spruce bark beetle, is widely considered a serious and destructive pest of Norway spruce tree species with the potential to impart extensive tree mortality upon infected forestry.
While the beetle is mainly a secondary pest, preferring stressed, weakened or felled trees, under the right environmental conditions, beetle numbers can increase enough to result in attacks on healthy forests too.
Eight-toothed spruce bark beetle
Since 2013, more than 100 million cubic meters of Norway spruce has been killed by the eight-toothed spruce bark beetle in Europe, the report revealed.
According to the Irish government, the eight-toothed spruce bark beetle is absent in Ireland, however, its presence was detected in southeast England last year, where it initiated localised breeding populations, which the UK government confirmed it is now working to eradicate.
2024 also marked the first time in which the bark beetle was identified on Sitka spruce, the principal commercial conifer grown in the UK, having traditionally thought to have only colonised Norway spruce species.
However, the new study revealed that the bark beetle is just as partial to Sitka spruce as it is to Norway spruce, which has repercussions for commercial forestry in both Ireland and the UK.
Forest Research scientist and author of the study, Dr. Daegan Inward said: “There has been lots of research about how Norway spruce and Ips typographus interact, but very little is known about the susceptibility of Sitka spruce to the beetle.
“Sitka is Britain’s most important forestry conifer species, yet we don’t have a clear picture of how readily the beetle will colonise and breed in it or understand how successfully Sitka spruce can defend itself against the kind of attacks that have killed so many Norway spruce trees in continental Europe.
“This research is an important step in building that knowledge.”
Research
Researchers conducted the study in the Forest Research quarantine containment facility in Surrey, a specialist chemical ecology lab at Rothamsted Research.
The results were verified in a spruce forest in the Ardennes region of Belgium with an endemic population of the beetle.
In doing so, the scientists discovered that Ips typographus is similarly attracted to Sitka spruce as it is to its primary host, Norway spruce, and has been proven to readily select fresh-cut Sitka spruce logs as a resource for breeding.
The study found that odours of aged wood from the two species were equally attractive to the bark beetle, and that fresh Sitka was found to be more appealing than fresh Norway spruce.
“While this study has advanced understanding of cut Sitka spruce as a suitable host for breeding, the logs used in our work have significantly reduced defences compared to living trees,” Dr. Inward continued.
“Defensive capabilities of live, growing trees will be different and more responsive. Our current work is therefore investigating the susceptibility to attack of live Sitka spruce trees in European-grown forests.
“This will provide a much clearer picture of the potential impact and risks of Ips typographus to Sitka spruce and how this can be addressed through forest management practices.”
According to the reserachers, when a tree is infested with eight-toothed spruce bark beetle, inspection of the bark, and the wood under the bark, usually reveals a linear gallery system, where the females lay their eggs.
This has led to the beetles being often referred to as ‘engraver’ beetles, due to the appearance of the galleries.
