How the ALB came to Switzerland

The Asian longhorn beetle (German Asiatischer Laubholzbockkäfer, ALB) is one of the most dangerous hardwood pests worldwide. Originally from Korea and China, it has been spread globally via packaging wood since 1996, first to the USA and then to Europe. 

As a priority quarantine organism, the ALB is subject to mandatory reporting and eradication. It is being combated consistently and at great expense. An open-field outbreak is only considered eradicated when no insects or symptoms have been detected for four consecutive years.

To date (as of August 2025), the ALB has mainly infested trees in residential areas. Its spread into forests would have devastating economic and ecological consequences.

Karte der Schweiz mit fünf markierten Orten: Berikon (grün, 2015-2019), Zell (rot, 2022-), Winterthur (grün, 2012-2016), Marly (rot, 2014-), Brünisried (rot, 2011-2017).
Since the first Swiss field discovery in 2011 in Brünisried (FR), three infestation sites have been eradicated (green), with eradication measures still ongoing at two other sites (red).

On the genetic trail of the ALB

Although the global spread of the ALB has been documented, information on the genetic patterns within local outbreaks is crucial for the efficient control of this invasive pest.

We therefore analyzed ALB samples (beetles, larvae, eggs, and pupae) from the first four outdoor infestations in Switzerland using microsatellites and gained intriguing insights, such as:

  • The ALB populations each originated from three to nine different females from China and South Korea. Such a small number of females therefore appears to be sufficient to establish a viable population. Whether such genetically impoverished invasive populations are viable in the long term remains to be tested.
  • At least three independent introductions and one transfer within Switzerland led to the four outbreaks.
  • Some females have almost certainly colonized several trees up to 400 m apart.
  • In Marly, the population had reproduced over several generations before it was discovered. The infestation was considered eradicated since 2018, but the new finding in 2024 belongs to the same genetic group.

Public enemy No. 1 for Swiss forests

It is no surprise that the ALB is so feared: its larvae bore large tunnels into living hardwood trees – even healthy ones – causing them to die within a few years.

Querschnitt eines Baumstamms mit Fraßspuren der ALB-Larve, Bereiche A bis F markiert
The young ALB larva first feeds under the bark in the bast (A), then penetrates the wood (B) and excavates a wide gallery in the wood (C). It enlarges the end of the gallery into a pupal chamber (D), where it pupates behind a plug of wood shavings (E). Finally, the adult beetle emerges through a perfectly round exit hole (F).