Essen, Germany (dpa) - Prices for the most commonly used wood for building houses and making furniture in Germany have collapsed following an invasion of the harmful bark beetle.Millions of spruce trees have already fallen victim to the voracious pests, and there is no end in sight to the infestation."The wood is not worth anything any more," Heidrun Buss-Schoene, director of the Foresters‘ Association of the state of North Rhine Westphalia, said.She said that trees that were between 60 and 100 years old were being sold off at prices as low as firewood.At the start of 2018, spruce prices were between 90 and 95 euros (104-110 dollars); they are now mostly selling around half that price.At the forest holding Wald und Holz (Forest and Wood), spokesman Michael Blaschke said losses were on average 30 per cent.Spruce is valued because its wood is easy to work and the trees have long, straight trunks. It is used mostly in construction and in the furniture, packing and flooring industries.A construction boom in Germany has led to a high demand for spruce, but in many years it has become a scarce commodity, according to one expert, Joerg Dommermuth of the regional forestry office in the Sauerland area of North Rhine Westphalia.