Steinernema kraussei S. carpocapsae S. feltiae S. glaseri S. kushidai S. intermedium S. affine S. cubanum S. bicornutum S. longicaudatum S. rarum S. scapterisci S. serratum S. thermophilum
Heterorhabditis bacteriophora subgroup Brecon
H. bacteriophora subgroup HP88
H. bacteriophora subgroup NC
H. megidis Nearctic group (Ohio, Wisconsin)
H. megidis Palaearctic group
Xenorhabdus bovienii X. nematophila X. bovienii X. poinarii X. japonica X. bovienii X. bovienii X. poinarii X. budapestensis X. beddingii X. szentirmaii X. innexi X. ehlersii X. indica
Photorhabdus luminescens luminescens
Pp. luminescens laumondii
Pp. temperata temperata
Pp. luminescens akhurstii
Steinernematid and Heterorhabditid nematodes attack a far wide spectrum of insects and are being exploited worldwide to manage crop insect pests. The host range of these nematodes varies with the species (Table 13.2) and it has been observed to
Table 13.2 Host suitability of some Steinernema sp. against various insect pests
S. seemae, S. masoodi, S. thermophilum,
S. glaseri, S. carpocapsae S. carpocapsae, S. seemae, S. thermophilum,
S. glaseri, S. masoodi S. carpocapsae
S. carpocapsae, S. feltiae, S. abbasi,
Heterorhabditis indica S. glaseri, S. carpocapsae S. carpocapsae
S. masoodi, S. seemae, S. carpocapsae,
S. thermophilum S. carpocapsae S. seemae, S. masoodi S. masoodi, S. seemae, S. carpocapsae S. seemae, S. masoodi, S. carpocapsae S. seemae, S. masoodi S. masoodi, S. seemae, S. carpocapsae S. masoodi, S. seemae, S. carpocapsae S. masoodi, S. carpocapsae
Greater wax moth (Galleria mellonella)
Rice moth (Corcyra cephalonica)
Black cutworm (Agrotis ipsilon) Tobacco caterpillar (Spodoptera litura)
White grub (Holotrichia consanguinea) Leaf minor (Liriomyza trifolii) Gram pod borer (Helicoverpa armigera)
Diamondback moth (Plutella xylostella) Legume pod borer (Maruca vitrata) Blue butterfly (Lampides boeticus) Bruchid (Callosobruchus sp.) Wheat flour beetle (Tribolium castaneum) Grey weevil (Myllocerus sp.) Bihar hairy caterpillar (Diacrisia obliqua) Mealybug (Centrococcus sp.)
infect over 200 species of insects belonging to different orders (Woodring and Kaya 1988). S. carpocapsae has been found to parasitize more than 250 insect species from over 75 families in 11 orders (Poinar 1975). The host range of nematodes largely depends on foraging strategy varying from cruising to ambusher (Campbell and Gaugler 1997). Cruisers have an active searching strategy, moves through the soil and are more effective against those insects, which are less mobile (Lewis et al. 1993; Campbell and Gaugler 1997). The cruise foraging species are Heterorhabditis sp. and S. glaseri (Lewis 2002). Ambushers nictate during foraging by raising nearly all of their bodies off the substrate. S. carpocapsae and S. scapterisci are the extreme ambushers and may nictate for hours at a time (Campbell and Gaugler 1993). Heterorhabditids have a better host-finding ability than the Steinernematids (Choo et al. 1989). Motility and attraction are also responsible for host-finding ability of nematodes. There is a third type having intermediate foraging strategy whereby nematodes raise themselves on substrate for a short while, and has been reported in some species like S. riobrave and S. feltiae (Griffin et al. 2005). Susurluk (2008) compared the vertical movement of Turkish isolates of S. feltiae (TUR-S3) and H. bacteriophora (TUR-H2) at different temperatures in the presence and absence of larvae of the host insects, G. mellonella. It was observed that nematodes of both species moved faster towards the bottom of the column when an insect was placed there. S. feltiae showed greater vertical dispersal ability than H. bacteriophora. The vertical movement of both species increased as the temperature increased and lower temperature depressed the movement of H. bacteriophora more than S. feltiae. The nematodes that had migrated different distances were compared for their infectivity to G. mellonella and the positive correlation between the distance travelled and infectivity indicated that there was a link between host-searching behaviour and infection behaviour in S. feltiae and to a lesser extent, also in H. bacteriophora.
The insects killed by nematodes are flaccid and do not undergo putrefaction because the mutualistic bacteria produce antibiotics, which prevent the growth of secondary micro-organisms. Also the cadaver differs in colour. Insects killed by steinernematids turn ochre, yellow brown or black, whereas those killed by heter-orhabditids turn red, brick- red, purple, orange or sometimes green (Sundarababu and Sankaranarayanan 1998). The insect infected with heterorhabditids, luminesce in the dark and this is due to the symbiotic bacteria Photorhabdus luminescens present in the intestine of the nematodes. The internal tissues of the killed insects become gummy or sticky.
Cannayane et al. (2007) conducted a laboratory experiment to test the pathogenic potential of H. indica and S. glaseri on cardamom root grub, Basilepta fulvicorne. After mortality the cadaver of B. fluvicorni exhibited brick red to brown colour when infested with H. indica and also luminescent under ultraviolet, whereas, yellow and flaccid nature was due to S. glaseri infestation.
The efficacy of Steinernematids and Heterorhabditids in the management of crop insect pests has been worked out by several workers in the past. Kumar et al. (2003) studied the efficacy of Heterorhabditids against S. litura collected from castor bean. The insect mortality was significant within 48 h of exposure when infective juveniles of Heterorhabditis were released against the larva of S. litura at the rate of 50, 75, 100, 125 and 150 infective juveniles per 100 g of soil. Narayanan and Gopalakrishnan (2003) reported that mustard sawfly, Athalia lugens proxima was highly susceptible to S. feltiae on radish under field condition. Toledo et al. (2006) for the first time demonstrated the infectivity of H. bacteriophora on third instar of tropical fruit fly, Anastrepha serpentina under laboratory conditions. Adjei et al. (2006) reported that S. scapterisci applied in stripe to a 10 ha bahia grass pasture reduced populations of mole crickets, Scapteriscus spp. by 79.2% over a period of 3 years. Infection on Tipula paludosa, a turf grass pest on golf courses was studied under laboratory condition against Heterorhabditis and Steinernema and it was observed that these nematodes were virulent against T. paludosa (Simard et al. 2006). Shapiro-Ilan and Cottrell (2006) also reported the susceptibility of lesser peach tree borer, Synanthedon pictipes against S. carpocapsae and S. feltiae. Cuthbertson et al. (2007) tested the efficacy of S. feltiae under both laboratory and glass house condition against sweet potato white fly, Bemisia tabaci. They observed 90% mortality in second instar of B. tabaci under laboratory condition and 80% under glass house condition. Ramos-Rodriguez et al. (2007) reported that under laboratory bioassay S. riobrave significantly reduced survival of larva, pupae and adults of a store grain pest red flour beetle, Tribolium castaneum. In an experiment, S. thermophilum when applied at 3000 infective juveniles per millilitre caused 46% mortality of diamondback moth infesting cabbage, whereas, mortality at 2,000 infective juveniles per millilitre was 40.5% (Somavanshi et al. 2006). Elawad et al. (2007) assessed the pathogenicity of H. indicus a local isolate of UAE against red palm weevil, Rhynchophorus ferrugineus. The result indicated that nematode was effective in declining the population of R. ferrugineus under both laboratory and field conditions. However, a higher concentration of H. indicus was required for field application. Khan et al. (2007) tested the pathogenicity of S. masoodi against final instars of six insect pests, i.e. G. mellonella, Pp. xylostella, Pieres brassicae, Corcyra cephalonica, Helicoverpa armigera and A. proxima. Six concentrations of the nematode were used, i.e. 25, 50, 75, 100, 125 and 150 infective juveniles per larvae. The nematode was found to be pathogenic to all the six insects with a considerable degree of variability in pathogenicity. Koppenhofer et al. (2008) conducted a series of laboratory and green house experiments to evaluate the comparative effectiveness of S. scarabaei, H. bacteriophora and H. zealandica for the control of second and third instar of cranberry white grub, Phyllophaga georgiana in cranberries. The result indicated that S. scarabaei was the most effective species causing 76-100% mortality of Pp. georgiana under green house condition. However, under laboratory condition S. scarabaei was more effective against third instar than second instar of Pp. georgiana. In an experiment under laboratory condition, Entonem and Larvanem, the two commercial products of S. feltiae and H. bacteriophora, respectively, were evaluated against Parahypopta caestrum, the major insect pest of Asparagus officinalis in Greece. S. feltiae caused insect mortality within 24 h, however, the highest level of mortality was observed at 48 h. In contrast, H. bacteriophora required 96 h to achieve the highest level of mortality. However, under field condition the two nematodes provided equal insect suppression (Salpiggidis et al. 2008).
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