Bacteria and yeasts associated with Sirex noctilio

Five genera of bacteria and yeasts commonly occur in the oviposition drills and larval galleries of Sirex noctilio. In exceptional circumstances, some of these microorganisms may be pathogenic while the yeast, Saccharomyces sp., is involved in the production of attractants of the rhyssine parasitoids Rhyssa and Megarhyssa spp. A possible role in larval nutrition is suggested but these microorganisms have no role in the phytotoxic effects of Sirex attack.