Entomopathogens as biological control agents are receiving a great deal of attention for the following reasons: they provide environmentally safe insect control; they can be engineered genetically, thereby changing their pathogenicity and persistence (Bonning and Hammock,1996.);(30) some of the proteinaceous toxins they produce can be transferred to and expressed in crop plants or other microorganisms (Raichon et al.1994)(31); or they can be used as inundative or inoculative biological agents. The use of most entomopathogens has focused on above ground pests. Yet, 90 percent of the pest species have one or more life stages in the soil (Klein,1990)(32). Several entomopathogens (e.g., Bacillus popilliae, B.thuringiensis subsp.japonensis Buibui strain,Beauveria spp.,Metarhizium spp.) are available for the control of soil dwelling pests, but to date the most successful have been the entomopathogenic nematodes.
Entomopathogenic nematodes in the families Steinernematidae and Heterorhabditidae have been known since 1929 and 1975, respectively (Glaser and Fox, 1930.;(55) (Poinar,G.O.Jr, 1975;(56), but they became commercially available only during the past decade 40 nematode families have been found associated with insects, only two families, Heterorhabditidae and Steinernematidae have widely been used as biological agents (Gaugler and Kaya 1990). Nematodes in the genera Steinernema spp. and Heterorhabditis spp. are found to be potential agents for control of insect pests. The free living, non feeding infective juveniles possess chemoreceptors, are motile, highly virulent, have high reproductive potential, and have the ability to seek out their hosts. They have the potential for long term establishment in soil through recycling on infected insects. Compatibility with other control strategies, pesticides, ease of production and ease of application are well established. Although some degree of success has been achieved against pests of cryptic habitats, their use in the foliar environment has been limited, with most attempts meeting with very little success (Begley,1990)(62). The major reasons for these failures within the foliar environment are generally considered to be due to temperature, UV radiation and desiccation. Spray application methods used to apply EPN also require critical assessment. Optimization of the application methods would ensure better efficacy (Lello,et. al.,1996.)(63). In India work on entomopathogenic nematodes started in 1966.
Extensive use of chemical pesticides has resulted in widespread insect resistance to pesticides and adverse effects on beneficial insects, wildlife, and human health throughout the world. In response, there has been increased demand for alternative and selective pest control agents, in particular, biological controls. In general, three kinds of biological control are recognized: natural, classical, and augmentative. Natural control is that population regulation which occurs in the habitats that co-evolving plants, predators, and prey occupy, Classical control involves the introduction, by man, of natural enemies to control both native and exotic pests. Augmentative control involves the manipulation, by man, of populations of natural enemies by altering environmental conditions, by aiding dispersal through inoculative releases of small numbers of individuals, or by greatly augmenting natural enemy populations to obtain immediate pest suppression through inundative releases of massive numbers of individuals .
Nematodes are morphologically, genetically and ecologically diverse organisms occupying more varied habitats than any other animal group except arthropods. They may occur as free-living organisms or as facultative or obligate parasites. Many species are endoparasites of insects pests of agricultural importance and they are broadly termed as entomopathogenic nematodes (= insect loving) or entomogeous nematodes (= insect associated) or entomopathogenic nematodes (= insect disease causing). Of all insects studied for biological control of insects,those in the families Steinernematidae and Heterorhabditidae have aroused the most interest, and information about them is growing exponentially.These two families mutualistically associated with bacteria are similar in their actions. Interest in entomopathogenic nematodes as biological control agents has heightened in recent years due to the adverse effects of chemicals and poor stability and persistence of other biological control agents. Biological control of pests using entomopathogenic nematodes is an ideal alternative, is economical, has long term control, without risk to non-target organisms. The EPNs are potential agents as they serve as vectors of bacteria, achieve a quick kill of target insect pests,have a broad host range,highly virulent,possess chemoreceptors,can be cultured easily in vitro,have a numerical but no functional response,are safe to vertebrates,plants and non targets,have been exempt from registration in USA,are easily applied using standard application equipment,are compatible with many chemical pesticides, and are amenable to genetic selection. Kaya and Gaugler (1993) presented a review (Link as below) There are currently hundreds of researchers representing 40 countries working on the development of entomopathogenic nematodes as biological control agents, and the number is increasing. This intense interest is a function of the impressive attributes of these beneficial nematodes that include ease of mass production, ease of application, host specificity, high lethality and safety to non-target organisms (Gaugler & Kaya, 1990; Kaya & Gaugler 1993). In addition, insect parasitic nematodes are commercially produced on four continents for the control of horticultural and agricultural soil-dwelling insect pests.
Rao and Manjunath(1966) discussed the use of DD 136 in the control of insect pests of rice, sugarcane and apple. In the seventies, Singh and Bardhan(1974) and Singh (1977) worked on mortality in laboratory and field trials, life cycle and compatibility of DD-136 with insecticides and fertilizers. Work on heterorhabditids is of recent origin. In Rice, high mortality of cutworm, Pseudoletia separataand leaf folder, Cirphis compta were obtained with DD 136 strain,S. carpocapsae in lab, green house and field experiments (Israel et al.1969). Ragi pink borer, Sesamia inferens, rice leaf folder, Cnaphalocrosis medinalis, rice borer, Chilo suppressalis, stem borer, Scirpophaga (=Tryporyza) incertulas and paddy gall midge, Orseolia oryzae were found highly susceptible. At temperature above 30°C nematodes were ineffective against Scirpophaga incertulas (Rao et al.1971). About 98% mortality of the folder, Srinivas and Prasad (1991) reported C. medinalis with S. carpocapsae. Enhancement of efficacy of spray was achieved with addition of 2% glycerin (Yadav & Rao,1970). They were found compatible with fertilizers and insecticides and tolerant to osmotic stress (Rao et al.1975,Das,P.K., 1977). Maize stem borer, Chilo partellus was parasitized by Neoaplectana sp. (Mathur et al.1966).
In Tobacco, DD-136 caused 66% mortality of cutworm, Spodoptera litura (Gupta, et. al., 1987). Narayanan and Gopalakrishnan (1987), found the effect of S. feltiae to the pre-pupa, pupa, and adult of S. litura. Complete mortality of S. litura pre-pupae was recorded at 10,000 and 1000 IJ. The pupae were less susceptible to nematode infection than pre-pupae and adults. However 20-60 mortality was observed in the case of 7-8 days old pupa.
In Groundnut, DD-136, Burliar, Melur and Cherikunnu strains of Heterorhabditis bacteriophora were tested by Bhaskaran et. al.,(1994) on red hairy caterpillar, Amsacta albistriga in field. DD 136 was most effective followed by cherikunnu and burliar strains. The Melur strain was ineffective. In Potato, the cutworms, Agrotis ipsilon and A. segetum were found parasitized Singh,S.P.,1977,(Singh,S.P., 1993). The DD-136 strain caused 100% mortality of chafer grubs, Anomala sp. (Rajeswari Sundarababu et al.,1984). Brinjal fruit borer, Leucinodes orbonalis, mustard sawfly, Athalia proxima (Singh and Bardhan,1974), castor semi looper, Paralellia algira (Gupta et al.,1987). Sivakumar et al.,(1989) found adult grasshoppers (Orthacris simulans), larvae of beetle, Draterius sp., citrus butterfly, Papilio aristolochiae and Ergolis merione were susceptible to Heterorhabditis bacteriophora.
Though the work on EPN in India has been initiated in 1960s, the scenario in India is not vivid. Concerted efforts were not made in many aspects till 1996. Extensive surveys were taken up by PDBC since 1996 in different parts of the country and documented different species and isolates of EPN in the country. Adopting the baiting technique (Bedding and Akhurst,1975.) many species have been documented throughout the world. This technique is the widely accepted and has been recommended for the collection of indeginous EPN population. In India, Poinar et al.(1992) described Heterorhabditis indica from Sugarcane ecosystem in Coimbatore. Further there have been no authentic records of occurrence of Steinernema sp. in the country. Ganguly and Singh,(2000) described a new species S. thermophilum from Delhi. Most of the workers engaged in EPN research in India find difficulty in identification of the species due to lack of adequate taxonomic expertise.
EPN research at Gujarat Agricultural University was started in 1980 the imported EPN, Steinernema glaseri (Steiner) Travassos (SBI, Coimbatore) was tested for its efficacy against some polyphagous insect-pests viz., white grub (Holotrichia consanguinea Blan.), cut worms (Agrotis ipsilon Huf. and Spodoptera litura Fab.) gram pod borer (Helicoverpa armigera Hub.) and Plutella xylostella through laboratory, pot and field tests at AICRP on Biological control of crop pests and weeds and subsequently in much detail at Department of Nematology. Research work on isolation of native EPNs (Vyas et al.,1998), in vitro mass production technique (Vyas et al.,1999), and field testing of EPNs was carried out at this center. At IARI, Delhi studies on taxonomy and biology were carried out and Ganguly & Singh (2000) described a new species of Steinernema from Delhi. Research on EPN has started in 1985 at TNAU since then studies on different aspects, viz. Natural occurrence, host range, mass multiplication and efficacy against insect pests under lab, microplot and field, of EPN was carried out under ICAR adhoc scheme and through M.Sc. and Ph.D. students research programs.
At Directorate of Rice Research, Rajendranagar, Hyderabad Entomopathogenic nematode, Ochieus sp (Fam: Rhabditidae) was isolated. Pathogenicity of Ochieus sp. was tested against egg mass of yellow stem borer and leaf folder, Cnaphalocrocis medinalis in rice.