Predators

Mesofauna may be predators or serve as prey for predaceous mites and other predators, such as beetles, fly larvae, centipedes, and spiders. Predatory nematodes feed upon all the other trophic groups of nematodes (Moore and de Ruiter, 1991) and represent only a small portion of the total nematodes in agricultural ecosystems (Wasilewska, 1979). Nematode predators (e.g., members of the orders Mononchida and Tripylida) and insect-parasitic nematodes (e.g., members of the families Stein-ernematidae, Diplogasteridae, Mermithidae) present in the soil may affect populations of their prey (Poinar, 1979; Small, 1987; Stirling, 1991).

Soil microarthropods can be important predators on small arthropods (e.g., proturans, pauropods, enchytraeids) and their eggs, nematodes, and on each other. Predation of insect eggs in agroecosystems may constitute a major influence of controlling microarthropod populations. Brust and House (1988) found that the mite Tyrophagusputrescentiae is an important predator of eggs of southern corn rootworm Diabrotica undecimpunctata howardi in peanuts. Chaing (1970) estimated that predation by mites accounted for 20% control of corn rootworms (Diabrotica spp.) and 63% control following the application of manure. Mite predation on root-feeding nematodes may be significant under some conditions (Inserra and Davis, 1983; Walter, 1988). For example, one adult of the mesostigmatid mite Lasioseius scap-ulatus and its progeny consumed approximately 20,000 Aphelenchus avenae on agar plates in 10 days (Imbriani and Mankau, 1983). Collembolan species may also consume large numbers of nematodes (Gilmore, 1970). For example, Entomobry-oides dissimilis consumed more than 1000 nematodes in a 24-h period. Furthermore, collembolans may consume large numbers of insect-parasitic nematodes and, thus, affect the efficacy of these nematodes used as biological control agents of soil-dwelling insect pests (Epsky et al., 1988; Gilmore and Potter, 1993).

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