Entomopathogenic nematodes (EPNs) are recognized as one of the effective bio-control agents of insects that are harmful to many agricultural crops. The two EPNs genera, Steinernema and ...Heterorabditis, are widely used nematodes. Insect pests infesting different agricultural crops and other plants, can be controlled using these nematodes. These beneficial EPNs can be mass produced using both in vivo, baiting using insects, and in vitro techniques, using solid or liquid fermentation. For laboratory trials, greenhouse experiments, or limited agricultural field trials, in vivo production of EPNs is most appropriate. As EPNs have a crucial part in the management of numerous insect pests of field crops, stored products/grains, mushroom culture, etc., they are valuable as eco-friendly products. Our focus in this paper is to present the various procedures and components involved in the in vivo mass production of EPNs and to provide a summary of factors that affect the in vivo mass production.
The entomopathogenic nematodes (EPNs) Steinernema and Heterorhabditis have long been described as specifically associated with endosymbiotic bacteria, but recent studies have revealed associations ...with more complex bacterial communities.The endosymbionts Xenorhabdus and Photorhabdus are the first bacterial circle of EPNs.The other associated bacterial taxa, the second bacterial circle, belong to other species, mostly Proteobacteria.Putative first, and a second, bacterial circles have also been described in the entomopathogenic bacterivorous nematodes, Caenorhabditis briggsae and Oscheius sp.The second bacterial circle might play a role in the parasitic cycle, that is, entry into the live insect, causing death, nematode reproduction in the insect cadaver, and EPN transmission and dissemination in soil.
Single host–symbiont interactions should be reconsidered from the perspective of the pathobiome. We revisit here the interactions between entomopathogenic nematodes (EPNs) and their microbiota. We first describe the discovery of these EPNs and their bacterial endosymbionts. We also consider EPN-like nematodes and their putative symbionts. Recent high-throughput sequencing studies have shown that EPNs and EPN-like nematodes are also associated with other bacterial communities, referred to here as the second bacterial circle of EPNs. Current findings suggest that some members of this second bacterial circle contribute to the pathogenic success of nematodes. We suggest that the endosymbiont and the second bacterial circle delimit an EPN pathobiome.
•S. carpocapsae and S. bicornotum showed the best efficacy in laboratory studies.•The highest mortality rate (%75) was obtained by S. bicornotum at 1000 IJs.•Field performance of EPNs were quite ...similar to those in laboratory studies.•The maximum mortality rate (55%) was achieved by H. indica in field studies.
In the present study, the virulence of some local entomopathogenic nematode (EPN) isolates (S. carpocapsae E-76, S. feltiae KCS-4-S, H. bacteriophora FLH-4-H, S. bicornotum MGZ-4-S and H. indica 216-H) recovered from the surveys conducted in Adana, Kayseri, and Kahramanmaras provinces on the 5th or 6th larval instar of Agriotes spp. (Coleoptera: Elateridae) were investigated under laboratory and field conditions. Laboratory studies were carried out in 100 ml plastic containers including autoclaved soil at different temperatures (25 and 30 °C) and concentrations (25, 50 and 100 IJs/cm2). The infective juveniles of S. carpocapsae E-76 and H. indica 216-H isolates were applied at the concentration of 1x106 IJs/m2 with a back pack sprayer with a 0.5 mm nozzle in the field trial. In the laboratory studies, the mortality rates generally increased with the increasing temperatures, concentrations and exposure times. The highest mortality rate (65%) was achieved by two isolates (S. bicornotum MGZ-4-S and S. carpocapsae E-76) at the highest concentration (100 IJs/cm2) 21 days after inoculation at 25 °C. The most efficient isolate at 30 °C was S. bicornotum MGZ-4-S and caused 75% mortality 21 days after treatment. In the field study, S. carpocapsae E-76 performed better than H. indica 216-H isolate and caused 55% mortality on the larval instar of wireworms. The current study suggests that some of the EPN isolates tested have good potential for the biological control of wireworm. However, further studies are needed to enhance the effectiveness of EPN isolates.
The tomato leaf miner, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), is a devastating pest worldwide affecting tomato production. Entomopathogenic nematodes (EPNs) are well known for their ...potential as biocontrol agents to control the emergence and development of this insect pest. Virulence and pathogenicity of five EPN strains isolated from different fields in Morocco were evaluated against the larval stage of T. absoluta. In laboratory assays, Steinernema feltiae strains (SF-MOR9 and SF-MOR10) showed significantly higher infectivity rates after 72 h compared to Heterorhabditis strains. In leaf bioassay, S. feltiae strains alongside H. bacteriophora (HB-MOR8) strain caused the highest larval mortality rate (80–100%) at 40–50 infective juveniles (IJs) cm−2 which confirms the importance of the dose applied. On top of that, EPNs were able to locate and accurately kill the insect larvae inside and outside leaf conditions. Subsequently, the results showed that both S. feltiae strains were significantly effective in pot experiments for both applied concentrations (40 and 50 IJs cm−2). In addition, the efficiency of these nematodes was assessed under field conditions. Both S. feltiae accessions had optimal effects against T. absoluta larvae with more than 80% mortality rate at 50 IJs cm−2. Heterorhabditis strain (HB-MOR8) significantly reduced larval occurrence with a more than 60% mortality rate when applied at the same dose. Therefore, the three tested indigenous EPN strains; SF-MOR9, SF-MOR10, and HB-MOR8 could be used as promising eco-friendly biological agents against T. absoluta in a broad agronomic range.
•Steinernema feltiae showed high virulence under laboratory and field conditions.•The highest larval mortality (84.7%) was recorded for S. feltiae (SF MOR10) at 50 IJs cm2.•EPNs caused a mortality rate similar to Chlorantraniliprole against T. absoluta larvae.•Moroccan EPNs could be a reliable eco-friendly insecticide alternative to chemicals for controlling T. absoluta larvae.
•Entomopathogenic nematodes (EPNs) in soil are attacked by natural enemies.•Bacteria, fungi, mites and collembolans are major mortality factors of EPNs in soil.•Deterrent compounds are produced by ...symbiotic bacteria of EPNs.•The compounds protect the nematode-killed insects from microbial invasion.•The compounds also protects nematode-killed insects from omnivores and scavengers.
Entomopathogenic nematodes (EPNs) in the families Steinernematidae and Heterorhabditidae are effective biocontrol agents against a number of important soil insect pests and are safe to vertebrates, plants and other non-target organisms with no negative effects on the environment. They are associated with mutualistic bacteria in the genus Xenorhabdus for Steinernematidae and Photorhabdus for Heterorhabditidae and are often referred to as the nematode/bacterium complex. The natural habitat of EPNs is the soil where the third-stage infective juveniles (IJs), the only free-living stage, can infect an array of insect hosts. However, the survival of the IJs is affected by various abiotic (i.e., temperature, moisture, soil texture, soil salinity, UV light, oxygen, and pH) and biotic (i.e., natural enemies, omnivores, scavengers, competitors, and plants) factors in the soil. In this review, we summarize the impact of the biotic factors, especially natural enemies, omnivores, scavengers, and competitors against EPNs and conclude that the major predators of the IJs appear to be nematophagous fungi, mites, and collembolans. Omnivores and scavengers, particularly, mites, collembolans, ants and birds, feeding on EPN-killed insects appear to be the major mortality factors on the developing nematodes especially of insects that are 2 days or less post infection. In addition, we discuss the defense mechanisms of EPN IJs against nematophagous fungi, and the protection of the nematode-killed insects by production of the scavenger deterrent factor produced by the mutualistic bacteria against omnivores and scavengers. By understanding the interactions between EPNs and their antagonists we can improve and increase the successful use of EPNs in biological control programs.
Entomopathogenic nematode (EPN) Heterorhabditis indica is a promising biocontrol candidate. Despite the acknowledged importance of EPN in pest control, no extensive data sets or maps have been ...developed on their distribution at global level. This study is the first attempt to generate Ecological Niche Models (ENM) for H. indica and its global Habitat Suitability Map (HSM) for H. indica to generate biogeographical information and predicts its global geographical range and help identify of prospective areas for its exploration and to help identify the suitable release areas for biocontrol purpose. The aim of the modeling exercise was to access the influence of temperature and soil moisture on the biogeographical patterns of H. indica at the global level. Global Heterorhabditis indica ecosystems. CLIMEX software was used to model the distribution of H. indica and assess the influence of environmental variable on its global distribution. In total, 162 records of H. indica occurrence from 27 countries over 25 years were combined to generate the known distribution data. The model was further fine‐tuned using the direct experimental observations of the H. indica's growth response to temperature and soil moisture. Model predicts that much of the tropics and subtropics have suitable climatic conditions for H. indica. It further predicts that H. indica distribution can extend into warmer temperate climates. Examination of the model output, predictions maps at a global level indicate that H. indica distribution may be limited by cold stress, heat stress, and dry stresses in different areas. However, cold stress appears to be the major limiting factor. This study highlighted an efficient way to construct HSM for EPN potentially useful in the search/release of target species in new locations. The study showed that H. indica which is known as warm adapted EPN generally found in tropics and subtropics can potentially establish itself in warmer temperate climates as well. The model can also be used to decide the release timing of EPN by adjusting with season for maximum growth. The model developed in this study clearly identified the value and potential of Habitat Suitability Map (HSM) in planning of future surveys and application of H. indica.
This study, highlighted an efficient way to construct habitat suitability map (HSM) for entomopathogenic nematode (EPN) potentially useful in the search/release of target species in new locations. The study showed that Heterorhabditis indica which is known as warm adapted EPN generally found in tropics and subtropics can potentially establish itself in warmer temperate climates as well. The model can also be used to decide the release timing of EPN by adjusting with season for maximum growth. The model developed in this study clearly identified the value and potential of HSM in planning of future surveys and application of H. indica.
Entomopathogenic nematodes (EPN) are well-established plant protection tools for the control of insect pests. The release of EPN species is often limited to species that are endemic in the country. ...Therefore, surveys to check for the presence of EPN species in the country are necessary. Here, a sampling and baiting method based on the in situ attraction of EPN to insects contained in a plastic tube is described. Heterorhabditis downesi was isolated from overgrown dunes at the Baltic coast and Steinernema feltiae from chromic luvisol further inland. This is the first report of the presence of H. downesi in Germany.
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•Commercially available Entomopathogenic nematodes were evaluated for medfly control.•Steinernema feltiae provided the highest suppression of emerging adult medflies.•The efficacy of ...nematodes for medlfy control in citrus trees was evaluated.•Application of 2.5 × 106Steinernema feltiae/m2 leads to 65 % adult medfly suppression.•Entomopathogenic nematodes can reduce medfly populations early and off-season.
The Mediterranean fruit fly Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) is an important pest of citrus and other deciduous fruit trees. There is a need for sustainable pest management tools and the use of entomopathogenic nematodes have been explored for controlling the stages of medfly that occur in the soil. We have investigated further this approach by assessing the efficacy of commercially available entomopathogenic nematodes applied early season or off-season when the medfly populations are passing through their annual bottleneck period, aiming at reducing their population before the growing season. In laboratory experiments, the efficacy of commercial strains of Steinernema carpοcapsae, Steinernema feltiae, Heterοrhabditis bacteriοphοra and H. downesi at doses of 1.5 × 106 IJs/m2 and 2.5 × 106 IJs/m2, at 15C° and 25C° was assessed. Steinernema feltiae was found to result in up to 70 % reduction of adult medfly emergence at a dose of 2.5 × 106 IJs/m2 and lower temperatures, confirming its superiority over other commercially available species. Field trials in citrus groves in Corinthos, Greece in Spring 2021 (early season) and Autumn 2021 (off-season) showed that a single application of S. feltiae at moderate dose regimes can provide about 62–65 % suppression of adult medlfies. Therefore, a single, moderate dose application of entomopathogenic nematodes early or off-season, which is more economically feasible can provide significant suppression of overwintering medflies and can be safely integrated with other tools for medfly management.
Below-ground insect pests are challenging to control because they are hard to target with control measures. Moreover, broad spectrum insecticides are or will soon be banned due to their negative ...effects on non-target organisms. In this study, we have developed a biological control method for the cabbage maggot Delia radicum (Diptera: Anthomyiidae), a significant pest of Brassicacean crops, based on a consortium of three biocontrol agents (BCAs). We chose the bacterium Pseudomonas chlororaphis because it can be used in a dual strategy against insect pests and fungal plant diseases, and combined it with the nematode Steinernema feltiae and the fungus Metarhizium brunneum that have a long history of commercial use against different pest insects. Our aim was to combine BCAs with different modes of action in order to achieve a stable and reliable biocontrol effect. We first tested double combinations of the bacterium with either the nematode or the fungus for improved potential to kill D. radicum in laboratory assays. We then evaluated the effect of double and triple combinations on D. radicum development and maggot-induced damage on radish bulbs in a series of pot experiments with artificial cabbage maggot infection performed in the greenhouse and outdoors and finally in a field trial with a natural infestation. Our results show that i) insecticidal pseudomonads are highly efficient in D. radicum control, ii) the three BCAs are compatible and neither inhibit each other’s infectiousness nor survival in the soil or on the roots, iii) synergistic effects of Pseudomonas-nematode and Pseudomonas-fungus combinations on maggot killing are possible, and iv) the triple combination reduced both pest survival in greenhouse experiments and maggot-induced damage on radish bulbs in the field by 50% each. The strategy we present here is a promising step forward to a reliable and efficient environmentally friendly biological control method for the cabbage maggot, which can also be adapted to other problematic below-ground pests.
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•Root-colonizing insecticidal pseudomonads can control the cabbage maggot Delia radicum.•In a biocontrol consortium, entomopathogenic pseudomonads, nematodes and fungi are well compatible.•Combinations of biocontrol agents resulted in more stable and efficient D. radicum control.•Application of the triple consortium in a field trial increased marketable radish by 50%.
The striped flea beetle, Phyllotreta sinuata is a serious pest of Chinese radish production. This insect larvae feed on roots of the host plant, pupate in the soil and adults live close to the soil ...surface. This study evaluated the efficacy of three entomopathogenic nematodes (EPN); Steinernema siamkayai, S. carpocapsae, and Heterorhabditis indica against various stages of P. sinuata. The results showed that all three EPN species were able to kill third-instar larvae, pupae and adults of P. sinuata under laboratory conditions. Larvae of P. sinuata were more susceptible to all three EPN species than the other two stages. Field evaluations indicated a reduction of P. sinuata populations and a decrease of root damaged length caused by the larvae of P. sinuata after 40 days of exposure. Furthermore, root weight and root diameter of Chinese radish in treatments with S. carpocapsae were higher than control treatments. This study presents evidence for the potential use of the three EPN species as bio-agents against P. sinuata on Chinese radish production in Thailand.
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•Steinernema siamkayai, Steinernema carpocapsae, and Heterorhabditis indica were tested against Phyllotreta sinuata.•The three entomopathogenic nematode (EPN) species were able to kill third-instar larvae, pupae and adults of P. sinuata.•Larvae of P. sinuata were more susceptible to all three EPN species than pupae and adults of P. sinuata.•Three EPN applications every ten days reduced P. sinuata damage under Raphanus sativus fields.
