An invasive species of beetle that has killed tens of millions of ash trees in North America could "spread unhindered" across Europe, researchers have warned.

 

The emerald ash borer, first recorded in the Moscow area in 2007, has become established in surrounding broadleaved woodlands, they observed.

 

The pest, which is expected to cost the US economy $10bn, has spread up to 25 miles each year, the team estimated.

 

The team of two UK and two Russian scientists found that the emerald ash borer (EAB) population had spread 146 miles (235km) west of Moscow and 137 miles (220 km) south of the Russian capital city.

 

In their paper, the team described EAB (Agrilus planipennis) as a "major threat to Fraxinus excelsior (European ash), and south of Moscow, where the beetle has become established in natural broadleaved woodlands in which F. excelsior is a major component, many of the ash trees are suffering severe dieback and mortality".

 

They added: "The abundance and almost continuous distribution of F. excelsior in these woodlands means that A. planipennis now has the opportunity to spread unhindered on a broad front to other countries in Europe."

 

The beetle is native to north-east China, the Korean peninsula, Japan, Taiwan, Mongolia and the Russian Far East.

 

The beetles' larvae feed on the surface layers of the wood of a tree, cutting off vital supplies of nutrients and water, causing branches and eventually the whole tree to die.

 

Although the adult beetles only live for a matter of weeks, an individual female can lay in excess of 200 eggs during their short lives but the average is estimated to be in the region of 30-60 eggs.

 

The researchers wrote: "The beetle has killed tens of millions of trees over the past 10 years and has raised concerns over the future of ash in North America.