In 1995, significant damage caused by Xylosandrus germanus (Blandford) was reported on round timber, both with bark and decorticated, of Norway spruce, Picea abies (Karst.), and fir Abies alba (Mill.). The insecticides used against Xyloterus lineatus (Ol.) and Hylecoetus dermestoides (L.), showed an insufficient to no effect against X. germanus. Between 1996 and 1998 the development of the populations were investigated, the effectiveness of insecticides tested and the influence of felling date, decortication and storage site investigated in correlation with the intensity of damage. The decreasing population density, the activity of the insects as well the recommendations for storage and removal of round timber are illustrated and discussed.

Summary

In 1995, Xylosandrus germanus (Blandf.) was first observed on round timber of Norway spruce, Picea abies (L.) H.K, and fir, Abies alba Mill., both with bark and decorticated, in the Swiss Central Plateau and in the Jura-region. In the same year, damages on approx. 20’000 m³ round timber were reported with a estimated loss in value of about 1 million Swiss Francs. The insecticides used against Xyloterus lineatus (Ol.) and Hylecoetus dermestoides (L.) showed insufficient to no effect against X. germanus.

From 1996 to 1998, a research project investigated the activity of the beetles was observed in the course of their flight and while gnawing round timber. At the same time, the effectiveness of insecticides on the basis of pyrethroids, chlorpyrifos and fenitrothione permitted in Switzerland has been tested. The influence of felling date, decortication and site of storage have been studied.

The population density has decreased since 1995. Monthly average temperatures of less than 0 °C during the winter time seem to negatively influence the population development. The flight occurs between late April and early August and can be monitored with ethanol traps. The bore dust ejected between mid-May and mid-August indicates gnawing activity of the beetles. The beetles bore themselves 2 to 33 mm (median value: 12 mm) deep into the sapwood. Thus, the loss in value caused by X. germanus does not reach the depth of damage caused by X. lineatus (median value: 28 mm) and H. dermestoides (median value: 37 mm). The relative high resistance of Xylosandrus beetles to insecticides, is most probably not due to genetic selection. A relative quick removal of the round timber from the forest, that is "just-in-time felling" and drying, is the best prevention against X. germanus. Decortication in the forest only leads to a reduction of damage, if carried out before the flight of X. lineatus.