The nematode-bacterium complex kills insects so rapidly that the nematodes do not form the intimate, highly adapted, host-parasite relationship characteristic of other insect-nematode associations, e.g., mermithids. This rapid mortality permits the nematodes to exploit a range of hosts that spans nearly all insect orders a spectrum of activity well beyond that of any other microbial control agent. In laboratory tests, S. carpocapsae alone infected more than 250 species of insects from over 75 families in 11 orders. The nematodes attack a far wider spectrum of insects in the lab where host contact is assured, environmental conditions are optimal, and no ecological or behavioural barriers to infection exist. For example, foliage feeding lepidopteran larvae are highly susceptible to infection in petridishes, but are seldom impacted in the field, where nematodes tend to be quickly inactivated by the environmental extremes (i.e., desiccation, radiation, temperature) characteristic of exposed foliage. Although EPNs possess an extremely broad laboratory host range, ecological and behavioural barriers restrict their natural host range. Temporal and spatial factors, such as synchronous life cycles and differing habitat preferences, also appear to determine the host rang . For example New Zealand populations of S. feltiae occur at the basis of tussock grass, where they have become adapted to parasitize lepidopteran larvae feeding on the roots of these grasses. These strains of S. feltiae are ineffective parasites of native scarabaeid larvae living in the same habitat. Behavioural barriers also restrict nematode efficacy to a few selected hosts or host groups. Some species are sit-and -wait strategists or ambushers that tend to stay near the soil surface where their specialized foraging behaviours (nictation, jumping) allow them to efficiently infect mobile host species (e.g., S. carpocapsae and S. scapterisci). Other species are widely searching foragers or cruisers that distribute themselves actively throughout the soil profile and are well adapted to infecting sessile or less mobile hosts (e.g., H. bacteriophora and S. glaseri). Most known species appear to be situated somewhere along a continuum between these two extremes (e.g; S. riobrave, S. feltiae). Cruisers, which are highly mobile, respond strongly to long-range host chemical cues and are therefore best adapted to find sedentary hosts.

Host recognition is a vital step in the life cycle of most parasites. In plant and animal parasitic nematodes, host recognition consists of a sequence of behavioural responses to an array of stimuli associated with host or host-related materials. The strategy that EPN employ to find hosts varies between species. Nematodes rely to some extent upon environmental cues for orientation toward, recognition of, or assessment of potential hosts. Ambushers and cruisers differ in their responses to host associated cues. Contact cues (host faeces or cuticle) are short range and provide specific information about the host. Volatile host cues are long range and usually provide general, directional information for host location. Cruisers have strong attraction to volatile cues containing CO2 whereas ambushers rely on host movement for successful parasitization and be relatively unresponsive to chemical host cues until after the host is located. Location of sedentary host in soil matrix necessitates the use of chemical cues, thereby exerting considerable selection pressure against individuals unable to follow chemical gradients to find hosts.

Host Range
Major target pests for entomopathogenic nematodes worldwide
Pest group Common nameLife Stage Application siteCommodity Nematode sp.2
Blattellidae German cockroach A.N BaitsApartment,buildings/structures Steinernema carpocapsae, Heterorhabditis zeylandica
Cerambycide Asian longborn beetle L Cryptic Forest trees, fruit trees Heterorhabditis bacteriophora, Heterorhabditis marelata, Steinernema carpocapsae
Bark beetle L Cryptic Forest Steinernema carpocapsae
Chrysomelidae Flea beetles L/A Soil Mint, potato, sweet potato, sugar beets, vegetables Steinernema carpocapsae
Colorado potato beetle L Foliage/soil Potatoes, vegetables Steinernema carpocapsae
Elm leaf beetle L Foliage Forest Steinernema carpocapsae
Striped cucumber beetle L Soil Vegetables Steinernema carpocapsae
Rootworms L Soil Corn, peanuts, vegetables Steinernema carpocapsae, Steinernema riobrave
Curculionidae Billbugs L Turf Turf Steinernema carpocapsae,Heterorhabditis bacteriophora
Curculionidae Billbugs L Turf Turf Steinernema carpocapsae,Heterorhabditis bacteriophora
Root weevils L Soil, rhizomes Banana, berries, citrus forest seedlings, hops, mint ornamental, sweet potato sugar beets, vegetables Steinernema carpocapsae,Heterorhabditis bacteriophora,Heterorhabditis marelata,Steinernema riobrave
Black vine weevil L Soil Straw, ornamental
Rice water weevil Soil Paddy Steinernema carpocapsae
Scarabaeidae White grubs L Soil, Turf Berries, field crops, ornamental,turf Heterorhabditis bacteriophora, Steinernema glaseri,Heterorhabditis marelata,Steinernema kraussei
Scolytidae Coffee berry borer L Cryptic Coffee berries Hb
Tenebrionidae Mealworm L Soil Poultry houses Steinernema carpocapsae
Agromyzidae Leaf miners L Foliage Ornamental, vegetables Steinernema carpocapsae
Anthomylidae Cabbage maggot L Soil Vegetables Steinernema carpocapsae, Steinernema feltiae
Ephydridae Shore flies L Soil Ornamental, vegetables Steinernema feltiae
Muscidae Filth flies A Baits Animal rearing units Steinernema feltiae, Heterorhabditis bacteriophora
Phoridae Phorid flies L Compost Mushrooms Steinernema carpocapsae
Sciaridae Sciarids Fungus goats L Soil Ornamental, vegetables Steinernema feltiae
Tephritidae Fruit flies L Soil Fruits and vegetables Steinernema carpocapsae,Steinernema feltiae, Heterorhabditis bacteriophora
Tipulidae Crane flies L Soil,turf Ornamental, turf Steinernema carpocapsae,Heterorhabditis marelata
House fly A Baits Animal rearing units Steinernema feltiae
HETEROPTERA A Steinernema feltiae
Coreidae Squash bug A/N Soil Vegetables Steinernema carpocapsae
LEPIDOPTERA A Steinernema feltiae
Carposinidae Peach borer moth L Soil Apple Steinernema carpocapsae
Cossidae Carpenter worms L Cryptic Ornamental, shrubs Steinernema carpocapsae
Leopard moth L Cryptic Apple, pear Steinernema carpocapsae
Noctuidae Cutworms L/P Soil,turf armyworms Corn,cotton Steinernema carpocapsae, Steinernema riobrave
Iris borer L Ornamental, vegetables Sc
Olethreutidae Codling moth L/P Cryptic Apple Steinernema carpocapsae
Pterophoridae Plume moth L Cryptic Artichoke Steinernema carpocapsae
Pyralidae Webworms L Soil, turf Cranberries, ornamental, turf Steinernema carpocapsae
Sesiidae Crown borers L Cryptic Berries Steinernema carpocapsae,Heterorhabditis bacteriophora
Grape root borer L Soil Grapes, berries Heterorhabditis bacteriophora,Heterorhabditis zeylandica
Peach borers L Cryptic Peaches, Cherries Steinernema carpocapsae,Heterorhabditis bacteriophora
Stem borer L Cryptic Cucurbits, ornamental,shrubs fruit trees Sc,Hb
Wood borers L Cryptic Ornamental,shrubs Steinernema carpocapsae,Heterorhabditis bacteriophora
Gryllotalpidae Mole crickets A/N Turf Turf,pastures, vegetables Steinernema riobrave
Acrididae Grasshoppers A/N Turf Turf,pastures Steinernema carpocapsae
Pulicidae Cat fleas L/P Soil, turf Pet/vet Steinernema carpocapsae
Thripidae Western flower thrip L Soil Ornamental, Vegetables Heterorhabditis carpocapsae,SfHeterorhabditis bacteriophora
Several Plant-parasitic nematodes All Soil,turf Ornamental,turf,vegetables Steinernema riobrave,Steinernema feltiae,Steinernema carpocapsae,Heterorhabditis bacteriophora,Heterorhabditis indica

Host Acceptance
An EPN can parasitize only a single host, so each infective nematode must carefully assess an insect before committing irreversibly. Nematodes must be able to recognize their hosts so they don't make an irreconcilable mistake and attack an unsuitable host. They are able to discriminate among potential hosts. S. carpocapsae is highly responsive to caterpillars, moderately responsive to white grubs and is unable to differentiate between millipedes and plastic. This correlates positively with the suitability of these insects as hosts, thereby providing an excellent measure of adaptation and an excellent means for making more accurate nematode-insect matches. Once a potential host has been contacted and recognized, the insect is not defenseless.
Spiracles are a key portal of entry of S. carpocapsae attacking caterpillars, but white grub spiracles are covered with sieve plates that preclude invasion via this route. The alternate penetration route for this nematode tends to be the gut; but whereas the highly susceptible wax moth has a thin, loose peritrophic membrane lining the gut, white grubs possess a thick, multi-layered protective membrane. Therefore only highly adapted nematodes such as S. glaseri are a good match against these insect pests.

Host Selection
Infection barriers are all part of the host selection process for EPN consisting of four sequential steps: 1) host-habitat finding, 2) host-finding, 3) host acceptance, and 4) host suitability. Each step acts as a sort of biological sieve, narrowing an experimental to a field host range. If our goal as practitioners is to match target insects with the nematode species best able to parasitize it, we must understand and appreciate each step.
1. Host-Habitat Finding. Parasite and host must coincide in time and space. Cabbage loopers are easy for nematodes to kill in the lab but tolerate the physical extremes characteristic of exposed foliage: rapid desiccation, high surface temperature, and exposure to solar radiation. Nematodes are soil adapted. The soil environment buffers them against extremes of the aboveground world. Overwhelmingly, nematodes are most effective when soil insects are the target pests.
2. Host-finding. In the proper habitat, IJs must locate insect hosts. Host-finding strategies can be divided into two broad categories: ambushing and cruising. Ambusher and cruiser strategies can be distinguished by their contrasting host search behaviours. Cruiser nematode species such as S. glaseri and H. bacteriophora tend to be highly mobile in searching comparatively large areas for hosts, whereas ambusher species tend to remain stationary. The key reason for this dichotomy in behaviour is nictation. Ambushers nictate, search by standing on their tail, elevating most of their bodies free in the air. The sit-and-wait approach to find hosts serves as a mechanism for host attachment. Ambushers are unable to detect hosts resting only a few millimetres away. By contrast, cruisers are unable to nictate but are highly responsive to host-released volatiles like carbon dioxide, which they use to orient toward insects. Ambushing is clearly a surface-adapted behaviour, as it is not possible to nictate effectively within the soil. And, indeed, soil sampling reveals that ambush species tend to be found in the upper soil stratum especially near the soil surface. Cruiser species are found distributed throughout the soil profile.
As ambushing is a stationary behaviour occurring at or near the soil surface, hence ambusher nematodes are best adapted to parasitize highly mobile, surface-adapted hosts like cutworms and armyworms. If cruising is a mobile behaviour that occurring below ground, then cruiser nematodes must be best adapted to parasitize sedentary, below ground hosts such as white grubs. Thus, understanding host-finding strategies helps to make efficacy predictions, thereby optimizing host-parasite matches.
Host finding is a continuum. Ambusher species such as S. carpocapsae and S. scapterisici form one end of the continuum and cruisers such as H. bacteriophora and S. glaseri form the opposite end. Other species, notably S. riobrave and S. feltiae, are intermediate, doing both ambushing and cruising. Yet where most species of the more than 40 species of EPN fall on the continuum is not known

Host Suitability
After a suitable host is located, recognized, and penetrated, the nematode's attack still may not succeed if the insect is able to respond with an effective immune response. The immune response also provides with clues for making the most appropriate host-parasite matches, since a strong immune response suggests a low level of adaptation. Thus, S. carpocapsae is a poor match for Popilia japonica larvae where encapsulation begins immediately and melanization is complete in a few hours. S. glaseri invasion elicits a weak immune response that is quickly defeated by the nematode-released anti-immune proteins. This would indicate that the latter nematode is the best match for control purposes, a prediction borne out by extensive field testing. Consideration of host suitability provides another measure useful in avoiding incompatible matches.

Host Range
Steinernematids and heterrorhabditids are reported to infect over 200 species of insects from several orders. Entire range of insects controlled with entomopathogenic nematodes have been reviewed by Georgis and Manweiler (1994) and several other authors (Kaya, 1985; Klein, 1990; Nickle, 1984; Wouts, 1991; Umamaheswari et al., 2004.). The insects killed or parasitized by the entomopathogenic nematodes includes armyworms, carpenter worms, cat fleas, crown borers, cutworms, filth flies, flea beetles, German cockroaches, leaf miners, mole crickets, phorid flies, plume moths, root weevils, sciarid flies, stem borers, webworms, white grubs, name a few.

Kaya, H.K., Burlando, T.M., Choo, H.Y & Thurston, G.S. (1995). Integration of entomopathogenic nematodes with Bacillus thuringiensis or pesticidal soap for control of insect pests. Biological Control 5(3): 432-441.
Klein, M.G. (1990). Efficacy against soil inhabiting insect pests. Pp. 195-214 In: R. Gaugler & H. K. Kaya (eds). Entomopathogenic nematodes in biological control. Boca Raton, FL: CRC Press

Nickle, W.R. (1984). History, development and importance of insect nematology. Pp. 627-653 in W. R. Nickle, ed. Plant and insect nematodes. New York: Marcel Dekker.

Wouts, W.M. (1991). Steinernema (Neoaplectana) and Heterorhabditis species. Pp. 855-897 in W.R. Nickle, ed., Manual of agricultural Nematology. New York: Marcel Dekker.

Umamaheswari,R., Sivakumar,M. & Subramanian,S. (2004). Host range of native entomopathogenic nematodes from Tamil Nadu. Insect Environment 10(4): 151-152

1. Neves-JM; Simoes-N; Mota-M. Evidence for a sex pheromone in Steinernema carpocapsae. Nematologica. 1998, 44: 1, 95-98; 11 ref.
AB: Sexual attraction and behaviour in S. carpocapsae was studied and is described. It was shown that virgin females produce an attractant which appears to be a non-strain specific sex pheromone.

2. Simoes-N; Caldas-C; Rosa-JS; Bonifassi-E; Laumond-C. 2000. Pathogenicity caused by high virulent and low virulent strains of Steinernema carpocapsae to Galleria mellonella. Journal-of-Invertebrate-Pathology. 75: 1, 47-54; 38 ref.
AB:The factors affecting virulence of Steinernema carpocapsae to Galleria mellonella were investigated by comparing high and low virulence strains, both free of symbiotic bacteria. The ability of strain Az27 to infect larvae was not significantly different from that of the Breton strain, but mortality occurred later in insects exposed to Az27 than in those exposed to the Breton strain, with LT50s of 75.2 and 27.3 h, respectively. Silk production and mobility were reduced in larvae 12 h after exposure to the Breton strain, with death occurring at 21-38 h after exposure. Az27 had less effect on mobility, and larvae containing a reduced number of nematodes were alive 5 days after exposure. The protein pattern of serum from healthy and infected G. mellonella was analysed using SDS-PAGE. The same pattern was observed in all cases, except for serum 36 h after injection of 30 infective juveniles of the Breton strain, in which a 42-kDa protein was present. Analysis of growth medium before and after incubation of infective juveniles, revealed that nematodes released products containing proteins. The profiles differed between the 2 strains. The Breton strain products had greater proteolytic activity than those of Az27.