A review on the role of predatory soil nematodes in the biological control of plant parasitic nematodes Zakaullah Khan, Young Ho Kim * Department of Agricultural Biotechnology, Center for Plant Molecular Genetics and Breeding Research, Seoul National University, Seoul 151-921, Republic of Korea Abstract Predatory nematodes feed on soil microorganisms including plant parasitic nematodes. They reduce populations of plant parasitic nematodes in virtually all soils because of their constant association with plant parasitic nematodes in the rhizosphere, and also release nutrients in plant-available forms, which may enable plants to better withstand nematode burden on their roots. Predation by nematodes of the orders Mononchida, Diplogasterida, Dorylaimida and Aphelenchida, has been studied but the data available in field/natural conditions are insufficient to conclude whether they are effective biocontrol agents of plant parasitic nematodes. However, among the different types of predators, diplogasterids are the most suited for biocontrol of nematodes, because of their short life cycles, easy culture, prey-specificity, chemotaxis sense and resistance to adverse conditions. This article summarizes progress to date and suggests ways to encourage the use of predatory nematodes as biocontrol agents in the management of plant parasitic nematodes. # 2006 Elsevier B.V. All rights reserved. Keywords: Aphelenchids; Diplogasterids; Dorylaimids; Mononchids; Predation; Biocontrol potential; Prospects 1. Introduction Soil inhabiting nematodes predominate over all other soil animals, both in numbers and species. On the basis of their feeding habits, nematodes are known as plant feeders, bacterial feeders, fungal feeders, algal feeders, animal predators, and omnivores (Yeates et al., 1993). All these types of nematodes co-occur in soil. The cost to world agriculture of nematode parasitism was estimated recently to be US$ 125 billion annually (Chitwood, 2003). Use of chemical nematicides is one of the primary means of controlling plant parasitic nematodes. However, their potential negative impact on the environment and human health has led to a total ban or restricted use of the most nematicides and an urgent need for safe and effective control options for plant parasitic nematodes (Zuckerman and Esnard, 1994; Nico et al., 2004). Biocontrol is one of the major options. Several types of organisms, including fungi, bacteria, viruses, protists, nematodes and other inverte- brates, have been found to parasitize or prey upon plant parasitic nematodes (Stirling, 1991). Sometimes, biocontrol measures are used alone; more often they are combined with chemical applications and cultural methods in systems of integrated pest management (IPM). When used as a part of an IPM program, biopesticides (bacteria, fungi, nematodes, protozoa, viruses) offer viable, safer and ecologically sound alternatives to chemical nematicides (Hom, 1996). Biocontrol advocacy of predatory nematodes dates back to the early 20th century. Nevertheless, their potential has only begun to be studied in recent years. * Corresponding author. E-mail address: yhokim@snu.ac.kr (Y.H. Kim).