Braunschweig, Germany  - A Germany-wide infestation with the citrus longhorned beetle, a major tree pest, was blamed Thursday on a shipment of bargain-price maple trees from China to the Netherlands.

Germany's Julius Kuehn Institute said the beetles, a serious threat not just to citrus crops but to many standing trees, had been found in two German states, Bavaria and North Rhine-Westphalia, but had probably been spread all over Germany by a supermarket chain.

The chain last month sold 100,000 of the trees as indoor pot plants. They had had been imported to the Netherlands from China in December.

Italy has been fighting an outbreak since 1997, with the infestation now extending to about 100 square kilometres. France stamped out an invasion in 2003 and the United States successfully defeated one infestation in 2001.

Buyers were asked to check the Acer palmatum trees, also known as Japanese maple, for round holes in the trunks indicating emerged beetles. Officials asked buyers to wrap infested pot plants in plastic and deliver them to plant-health authorities.

The pest, scientific name Anoplophora chinensis, is on a European Union schedule of biological threats.

Dutch authorities have impounded a fresh consignment of 25,000 of the pot plants from China and they are likely to be destroyed, said Gerlinde Nachtigall, spokeswoman for the Kuhn institute, which is Germany's federal plant-health agency.

The shiny black beetle is usually 21 to 37 millimetres long. (dpa)