The Impact of Fungal Extracts on Leaf Litter on the Food Preference of Gammarus roeselii

We investigated the effect of methanol and methanol/methylene chloride extracts of the oomycete Pythium sp. JN 1‐b and of the fungi Ascomycete sp. PVSo8, Fusarium sporotrichoides, and Cylindrocarpon sp. 94‐2057 on the food preference of Gammarus roeselii. The preference for leaf discs coated with these extracts compared to uncoated leaf discs was tested in food‐choice assays. Methanol extracts of all strains repelled G. roeselii, and the effect of the extract concentration on relative consumption was strain specific. The repellent effect of these extracts, especially of extracts of Cylindrocarpon sp., decreased when the fungi were grown on leaf extract medium as opposed to synthetic medium containing sucrose. None of the methanol/methylene chloride extracts affected the food preference of the gammarid. We conclude that biologically active compounds were extracted from fungi and an oomycete were soluble in methanol but not in methanol/methylene chloride. Only repellent activity was observed with the extracts, and relative ratios of repellents and attractants might determine the consumption of fungi by G. roeselii. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)