Biogeographical observations on four scolytids (Coleoptera, Scolytidae) and one lymexylonid (Coleoptera, Lymexylonidae) in Wallonia (Southern Belgium)

Following a very sudden, early and deep frost at the end of autumn 1998, the availability of weakened trees (mainly beech trees) reached very high levels in Southern Belgium in the spring of 1999. Consequently, the ambrosia beetles Trypodendron domesticum L. and T. signatum (Fabricius) (Coleoptera, Scolytidae) initiated outbreaks and, in 2000 and 2001, they heavily contributed to the depreciation of nearly 1,600,000 m(3) of stem volume (to upper limit girth of 22 cm) in the natural regions of ``Ardenne'' and ``Belgian Lorraine''. Because of the lack of biogeographical data on both insects, of their conspicuous aggressiveness towards apparently healthy trees and of the economic importance of the beech wood chain in Belgium, a large-scale survey was undertaken in 200 1, in order to outline the range of both ambrosia beetles in Wallonia. To this effect, a network of 172 traps baited with ethanol was set Lip, attempting to cover the Walloon beech forest as representatively as possible. Two other scolytids and one lymexylonid were also frequently caught, which made it possible to outline their regional distribution too. Although the damage was limited to the Ardenne and Belgian Lorraine, T domesticum and T signatum are widespread throughout Wallonia. We discuss these results, their long-term validity, the secondary pest status of these insects and the need for a permanent monitoring of the major forest pest species and diseases.