Feeding preferences for microfungi of six oribatid mites from two beech forests (Fagus sylvatica) in Germany, Gottinger Wald and Selling, were investigated. Six microfungi which were isolated from the L2-litter layer of the Gottinger Wald (Cladosporium herbarum, Trichoderma viride, Mortierella elongata, Mucor hiemalis, Penicillium sp.1 and a sterile dark form) were first offered simultaneously and then separately to three species of oribatid mites from this site (Steganacarus magnus, Acrogalumna longipluma and Hypodamaeus riparius). Also, six microfungi from similar fungal taxa which were isolated from the F-horizon of Solling (Cladosporium cladosporioides, Mortierella ramanniana, Mortierella parvispora, Mucor hiemalis, Penicillium sp.2 and a sterile dark form) were offered simultaneously and separately to three species of oribatid mites from this site (Cepheus dentatus, Nothrus silvestris and Hypochthonius rufulus). Feeding choice experiments were carried out separately for each oribatid mite species. Generally, oribatid mites from the two different forests preferred similar microfungal taxa as food substrate. The ranking of fungal taxa was very similar in tests where fungi had been offered simultaneously and separately. The oribatid mites studied preferred dark, pigmented fungi (Dematiacea) to hyaline forms. The reason for this preference remains speculative; food quality of dematiaceous fungi might be superior to that of hyaline fungi or oribatid mites may prefer to feed on dematiaceous fungi because they produce more effective exoenzymes ('external rumen'). Despite the general preference for dematiaceous fungi, food selectivity of the oribatid mite species studied differed and the species were ranked in respect to their food specialization: Steganacarus magnus > Acrogalumna longipluma > Cepheus dentatus > Nothrus silvestris > Hypodamaeus riparius, Hypochthonius rufulus. The consequences of selective feeding of oribatid mites on the structure of fungal communities are discussed.
