Heterorhabditis, Steinernema and their bacterial symbionts — lethal pathogens of insects

Burnell, Ann M.; Stock, S. Patricia

doi:10.1163/156854100508872

Cited by 188 publications

(128 citation statements)

References 58 publications

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“…After locating a living host insect, nematodes enter the hostÕs hemocoel and release symbiotic bacteria Gaugler 1993, Burnell andStock 2000). These bacteria produce compounds that are toxic to the insect host and suppress its immune system, eventually killing the host (Boemare 2002a, Park andStanley 2006).…”

Section: Discussionmentioning

confidence: 99%

“…These bacteria produce compounds that are toxic to the insect host and suppress its immune system, eventually killing the host (Boemare 2002a, Park andStanley 2006). InterspeciÞc variation exists in the bacterial species associated with entomopathogenic nematodes (Burnell andStock 2000, Boemare 2002b), and these bacterial species in turn differ in the insecticidal toxins they produce (Forst andNealson 1996, Chattopadhyay et al 2004). Differences among symbiotic bacteria also may have contributed to the differences in Þtness costs observed in this study.…”

Section: Discussionmentioning

confidence: 99%

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Effects of Four Nematode Species on Fitness Costs of Pink Bollworm Resistance to Bacillus thuringiensis Toxin Cry1Ac

et al. 2010

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Evolution of resistance by pests can reduce the efficacy of transgenic crops that produce insecticidal toxins from the bacterium Bacillus thuringiensis Berliner (Bt). In conjunction with refuges of non-Bt host plants, fitness costs can delay the evolution of resistance. Furthermore, fitness costs often vary with ecological conditions, suggesting that agricultural landscapes can be manipulated to magnify fitness costs and thereby prolong the efficacy of Bt crops. In the current study, we tested the effects of four species of entomopathogenic nematodes (Steinernematidae and Heterorhabditidae) on the magnitude and dominance of fitness costs of resistance to Bt toxin CrylAc in pink bollworm, Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae). For more than a decade, field populations of pink bollworm in the United States have remained susceptible to Bt cotton Gossypium hirsutum L. producing CrylAc; however, we used laboratory strains that had a mixture of susceptible and resistant individuals. In laboratory experiments, dominant fitness costs were imposed by the nematodeSteinernema riobrave Cabanillas, Poinar, and Raulston but no fitness costs were imposed bySteinernema carpocapsae Weiser, Steinernema sp. (ML18 strain), or Heterorhabditis sonorensis Stock, Rivera-Orduño, and Flores-Lara. In computer simulations, evolution of resistance to CrylAc by pink bollworm was substantially delayed by treating some non-Bt cotton refuge fields with nematodes that imposed a dominant fitness cost, similar to the cost observed in laboratory experiments with S. riobrave. Based on the results here and in related studies, we conclude that entomopathogenic nematodes could bolster insect resistance management, but the success of this approach will depend on selecting the appropriate species of nematode and environment, as fitness costs were magnified by only two of five species evaluated and also depended on environmental factors. RightsWorks produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted. ABSTRACT Evolution of resistance by pests can reduce the efÞcacy of transgenic crops that produce insecticidal toxins from the bacterium Bacillus thuringiensis Berliner (Bt). In conjunction with refuges of non-Bt host plants, Þtness costs can delay the evolution of resistance. Furthermore, Þtness costs often vary with ecological conditions, suggesting that agricultural landscapes can be manipulated to magnify Þtness costs and thereby prolong the efÞcacy of Bt crops. In the current study, we tested the effects of four species of entomopathogenic nematodes (Steinernematidae and Heterorhabditidae) on the magnitude and dominance of Þtness costs of resistance to Bt toxin Cry1Ac in pink bollworm, Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae). For more than a decade, Þeld populations of pink bollworm in the United States have remained susceptible to Bt cotton Gossypium hirsutum L. producing Cry1Ac; however,...

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Effects of Four Nematode Species on Fitness Costs of Pink Bollworm Resistance to Bacillus thuringiensis Toxin Cry1Ac

et al. 2010

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“…Thus, interest in studying these nematodes has increased dramatically in recent years, not only to address aspects related to biological control, but also regarding basic research areas such as ecology, biodiversity, evolution, biochemistry, symbiosis and molecular genetics (review by Burnell & Stock, 2000).…”

Section: Introductionmentioning

confidence: 99%

Morphological characterisation of three isolates of Heterorhabditis Poinar, 1976 from the `Irish group' (Nematoda: Rhabditida: Heterorhabditidae) and additional evidence supporting their recognition as a distinct species, H. downesi n. sp.

2002

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The morphological variation of three representative isolates of the 'Irish group' of Heterorhabditis was examined. First generation hermaphrodites were characterised by having a blunt and mucronate tail. Females (second generation) and third-stage infective juveniles were also distinguished by the morphology of the tail and the presence of a refractile projection in the tail tip. Males were characterised by the position of the excretory pore and by the value of ratio SW. These morphological features do not fit the description of currently recognised Heterorhabditis species, and provide additional evidence in support for the consideration of the Irish group as a new species. A description of this species, as H. downesi n. sp., is provided.

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“…The biology and behaviour of entomopathogenic nematodes have been extensively reviewed (e.g. Kaya & Gaugler 1993;Burnell & Stock 1999;Lewis et al 2006). The infective juvenile, a specialized third-stage juvenile, seeks out and enters insect hosts through the mouth, anus and spiracles, and through the intersegmental membranes in some hosts.…”

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Pine weevils modulate defensive behaviour in response to parasites of differing virulence

2010

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Grooming and avoidance of contaminated areas are among the behavioural defences employed by animals against parasites. Antiparasite defence behaviour is costly in terms of time, energy and/or food foregone and therefore animals are expected to modulate their defences depending on the risk of attack and/or the severity of the symptoms caused. We tested the hypothesis that an insect host invests more in defence against more virulent (more likely to cause death) than less virulent parasites. We tested avoidance and grooming of adult pine weevils, Hylobius abietis, in response to infective juveniles of two species of entomopathogenic nematodes, the more virulent Steinernema carpocapsae and less virulent Heterorhabditis downesi. Weevils avoided feeding on a substrate contaminated with S. carpocapsae but not H. downesi. Weevils also groomed more when their bodies were contaminated with S. carpocapsae than either H. downesi or water. We also made direct observations of nematodes on weevils. When equal numbers of nematodes were applied to weevils more S. carpocapsae than H. downesi moved actively on the weevil's cuticle. Thus, the differential response of weevils to the two nematode species can be explained by the weevils detecting the more aggressive behaviour of S. carpocapsae than H. downesi, which corresponds to a higher probability of death. Ó

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Heterorhabditis, Steinernema and their bacterial symbionts — lethal pathogens of insects

Cited by 188 publications

References 58 publications

Effects of Four Nematode Species on Fitness Costs of Pink Bollworm Resistance to Bacillus thuringiensis Toxin Cry1Ac

Effects of Four Nematode Species on Fitness Costs of Pink Bollworm Resistance to Bacillus thuringiensis Toxin Cry1Ac

Morphological characterisation of three isolates of Heterorhabditis Poinar, 1976 from the `Irish group' (Nematoda: Rhabditida: Heterorhabditidae) and additional evidence supporting their recognition as a distinct species, H. downesi n. sp.

Pine weevils modulate defensive behaviour in response to parasites of differing virulence

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