Historical Background

Nematodes from more than 30 families are known to be associated with insects and other invertebrates (Poinar 1979, 1990; Kaya and Stock 1997). However, only a few have established their potentialities as host enemies, while majority of them are more associated either for transport and dissemination or for sharing the same habitat (Sundarababu and Sankaranarayanan 1998). The nematodes from seven families, viz., Mermithidae, Allantonematidae, Sphaerularidae, Tetradonematidae, Phaenopsity-lenchidae, Steinernematidae and Heterorhabditidae are important from biological control of view (Kaya and Stock 1997). Steinernematidae and Heterorhabditidae are of much interest and drew lot of attention on the part of research workers and practitioners (Lacey et al. 2001). These nematodes possess many attributes of parasitoids and pathogens. They are analogous to parasitoids because they have chemoreceptors and can actively search for their hosts (Kaya and Gaugler 1993; Gaugler et al. 1997). Their similarity to pathogens is due to their association with mutualistic bacteria, viz., Xenorhabdus and Photorhabdus for steinernematids and heterorhabditids, respectively. The nematode-bacterial complex is highly virulent, killing its host within 48 h through the action of mutualistic bacteria, can be cultured in vitro, have a high reproductive potential (Kaya and Gaugler 1993), have wide range of hosts, yet pose no threat to plants, vertebrates and many invertebrates (Akhurst 1990; Kaya and Gaugler 1993).

Steinernematidae comprises two genera: Steinernema and Neosteinernema. Steinernema has more than 50 species (Ganguly 2006), whereas Neosteinernema has only one species (Nguyen and Smart 1994). The family Heterorhabditidae has one genus Heterorhabditis with eight reported species (Adams and Nguyen 2002). However, these figures have increased as in the last few years a number of new species belonging to Steinernema and Heterorhabditis have been described from different parts of the world. Phan et al. (2005) described Steinernema robustispiculum from Vietnam. S. seemae and S. masoodi were described from India (Ali et al.

2005a), S. khoisanae from South Africa (Nguyen et al. 2006a), S. leizhouense from southern China (Nguyen et al. 2006b), S. hebeiense from northern China (Chen-ShuLong et al. 2006), S. ashiuense from Japan (Phan et al. 2006), S. sichuanense from east Tibetan mountains, China (Mracek et al. 2006), S. cholashanensen from Sichuan province of China (Nguyen et al. 2008a), S. weiseri from Turkey (Unlu et al. 2007), S. costaricense and S. puntauvense from Costa Rica (Uribe-Lorio et al. 2007), Heterorhabditis safricana from western cape province of South Africa (Malan et al. 2008) and H. georgiana from Georgia, USA (Nguyen et al., 2008b).

The first entomopathogenic nematode, Aplectana kraussie was reported by Steiner (1923), which was later named as S. kraussie by Travassos (1927). However, biocontrol potential of entomopathogenic nematode under field condition was recognized when Glaser (1932) reported the suppression of Japanese beetle with the application of Neoaplectana glaseri. Application of the nematode to 73 field plots in New Jersey resulted in 0.3-81% pest suppression and its persistence was noticed for 8.5 years after treatment (Glaser 1932; Glaser and Farrell 1935; Glaser et al. 1940). Schneider (1859) described the association of a nematode with the slug Arion ater. Maupas (1900) established culture of a nematode, Phasmarhabditis hermaphrodita (which he called Rhabditis causenelli) on rotting flesh and the dauer larvae used for this purpose was found in the intestine of A. ater. However, Pp. hermaphrodita was first described as a potential biocontrol agent by Wilson et al. (1993a). In 1994, the commercial product of this nematode was released for use by home gardeners under the trade name Nemaslug® (Glen et al. 1994, 1996). This nematode has now been on sale in several European countries (Ester and Wilson 2005).

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