Microbial-feeding mesofauna feed on fungi (including mycorrhizae), algae, slime molds, and bacteria by removing them from clumps of decaying material or soil aggregates (Moore and de Ruiter, 1991). Generally, bacterial-feeding nematodes such as Cephalobidae and Rhabditidae (Neher and Campbell, 1996) are abundant in agricultural ecosystems (Wasilewska, 1979; Popovici, 1984). Consumption of microbes by soil mesofauna alters nutrient availability by stimulating new microbial growth and activity plus releasing nutrients immobilized previously by microbes.
In general, fungal feeding is the dominant trophic function of microarthropods. Collembolan species have preferred food sources which are maintained even after the material has passed through the digestive tracts of other animals. For example, the collembolans Proisotoma minuta and O. encarpatus feed upon the soilborne fungal plant pathogen Rhizoctonia solani which causes damping-off disease on cotton seedlings (Curl et al., 1988). These collembolan species prefer feeding on the fungal pathogen in soil compared with the biocontrol fungi Laetisaria arvalis, Trichoderma harzianum, and Gliocladium virens (Curl et al., 1988). Additionally, collembolan species can distinguish and graze selectively on different species of vesicular-arbuscular mycorrhizae (Thimm and Larink, 1995).
Almost all oribatid mites are microbial feeders. Examples of microbial feeding also occur in the Mesostigmata (Ameroseiidae, Uropodidae) and Prostigmatida (Tarsonemidae, Nanorchestidae, Stigmaeidae Pygmephoridae, Eupodidae, and Tydeida). Although many microarthropods are microbial feeders, recent studies indicate that other arthropods are omnivorous and shift feeding behavior as food resources change (Walter, 1987; Mueller et al., 1990).
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