Aliens vs Predators... war on beetles that threaten our forests

DEEP in the heart of Scotland’s forests, a war is raging on a microscopic scale – and the stakes could not be higher.

A tiny beetle is posing a major threat to the nation’s £1 billion forestry industry.

Worried forestry chiefs say containment of the insect, known as the great spruce bark beetle, is ‘no longer possible’ as it advances and targets Sitka spruce, Scotland’s most economically important tree.

But now a predator beetle is being deployed by scientists in a desperate bid to slow down its progress.

Rhizophagus grandis – specially bred in a lab outside Edinburgh – is so adept at hunting its prey that it has a strike rate of up to 90 per cent.

The insect is already in operation across southern Scotland, where the spruce bark beetle, Dendroctonus micans, thought to have been accidentally imported from mainland Europe, has been attacking forests after working its way up through England and Wales.

Paddy Robertson, Scottish Forestry’s tree health planning and contingency manager, said: ‘Currently, spread is restricted to southern Scotland with the ongoing risk that it will move north.

‘Containment is not possible, but the sector has found a way to live with this pest using a specific predator beetle.

‘Rhizophagus grandis is bred in a facility just outside Edinburgh by colleagues in Forest Research and typically 25 of these beetles are released wherever new populations of Dendroctonus micans are found.

Although eradication cannot be achieved using this method, it is being used to effectively manage the situation.’

The bark beetle has left a trail of devastation across Asia and Europe but early signs are that Rhizophagus grandis, its natural predator in the wild, has been able to slow down its progress and reduce some of the risk to Sitka and Norway spruce, which make up around half of the UK’s forests and are linked to 30,000 industry jobs in Scotland.

In the warm summer months, the female Dendroctonus micans tunnel into conifers to lay hundreds of eggs. The larvae then feed and grow inside the host, eventually killing it.

The insects spread within a short range of already infested trees but can fly up to several miles in good weather conditions when temperatures hit 22.5C (72.5F).

Regular surveys carried out by Scottish Forestry aim to locate infested trees and the predator beetle is deployed, laying its own eggs when it finds a population of bark beetles that its larvae can feed on.

Labs in England and across Europe have also been breeding the beetle in a bid to protect threatened sites.

One tree surgeon said: ‘Many foresters are concerned about the increasing threat to Sitka, given the huge part it plays in the Scottish economy.

‘If things get out of control, it could have a devastating impact.’

The beetle is the latest threat to Scotland’s forests, particularly in the south-west, which has already seen larches come under attack from a highly infectious mould, Phytophthora Ramorum.

Felling is currently the only way to slow down its spread and impact. Worryingly, it can also switch between species and is known as ‘sudden oak death’ in the United States.