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'Preference is measured on the scale of 0 to + 1 for prey accepted and 0 to - 1 for prey rejected. 2Number of combinations a prey was killed more than other species. Adapted from Bilgrami et al. (2005).

'Preference is measured on the scale of 0 to + 1 for prey accepted and 0 to - 1 for prey rejected. 2Number of combinations a prey was killed more than other species. Adapted from Bilgrami et al. (2005).

Diplogasterids can be reared on either prey nematodes or bacteria, both by in vivo or in vitro methods, since they are facultative and biphasic. Diplenteron colobocercus, B. degressei, M. fortidens, M. longicaudatus and M. gaugleri have been successfully maintained on Caenorhabditis, Rhabditis, Panagrellus, Cephalobus, bacteria or on a combination of nematode and bacteria for multiple generations over a period of several months. In a study on reproductive capacity of Mononchoides, cultures with 25 adult female nematodes per 5.5-cm agar Petri dish were started with E. coli. After 20 days at 30°C, culture plates averaged an impressive 10 376 individuals. The oviposition rate was 8-10 eggs day-1 female-1 (Siddiqi et al., 2003).

Mononchs possess significant potential to reduce populations of phytoparasitic nematode under field conditions, but they were never considered as a good biocontrol agent. These predators are fastidious to culture due to their localized distribution in field, long life cycles and low rate of fecundity. In contrast, stylet bearing predators appear as better biocontrol agents since they are widely distributed and occur naturally at high densities. However, their long life cycle and culture conditions hinder any practical application. Pillai and Taylor (1968) cultured diplogasterids on a dixenic culture of bacteria and Aphelenchus avenae. Prey nematodes and bacteria have supported growth and development of diplogasterid predators, although some appeared to provide better nematode reproduction than others.

2.6. Conservation

Predatory nematode conservation under natural conditions could make their practical utilization possible (Bilgrami & Brey, 2005). As compared to insects and other beneficial predatory nematodes, conservation is simple and cost-effective. Their population and predatory activities may be stimulated to counter parasitic nematode populations in the field. More studies are needed to develop methods for predatory nematodes conservation under natural habitats.

Neem (Azadirachta indica) products e.g., leaf powder, sawdust and oilseed cake, used as organic amendments, showed encouraging results in maintaining and conserving predatory nematode densities in the field (Akhtar, 1995; Akhtar & Mahmood, 1993). Mulching may be another option to improve conservation of predatory nematodes in the field. Mulching was found effective in stabilizing a Iotonchus tenuicaudatus population feeding on Tylenchulus semipenetrans and Helicotylenchus dihystera in orange orchards (Rama & Dasgupta, 1998). More studies are needed on the role of organic soil amendments and nitrogenous compounds in predatory nematode conservation.

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