The Woodwasp Sirex noctilio and Its Associated Fungus Amylostereum areolatum in Europe

Abstract

The current knowledge about the biology and ecology of siricid woodwasps and their Amylostereum mutualistic fungi, with a specific focus on Sirex noctilio and Amylostereum areolatum, are summarized from a European perspective. The woodwasp females deposit their eggs together with fungal spores and toxic mucus in single or multiple drills. The symbiotic fungus supports the development of the larvae, which usually takes 2 years. The fungus propagates vegetatively through the formation of asexual spores in the teneral females and is stored in the wasps’ mycangia. Both A. areolatum and the related species A. chailletii are known to have vegetative compatibility groups as a consequence of the symbiosis with woodwasps. Among the natural enemies of the woodwasps, woodpeckers have a minor significance in Sirex mortality compared to parasitoids. Particularly the parasitic Ibalia species can account for 40–70% larval mortality. Like all European woodwasps, S. noctilio preferably colonizes newly dead, damaged or greatly weakened trees with considerable needle loss and low moisture content. Thus, unlike in the countries where it has been accidentally introduced, S. noctilio causes hardly any pine mortality in Europe and is economically irrelevant.