A systematic review on research trends and commercialised entomopathogenic nematodes: A global perspective

Entomopathogenic nematodes in the families Steinernematidae and Heterorhabditidae are ubiquitous soil-dwelling obligate parasites of arthropods and are used commercially to suppress soil-dwelling insect pests in agricultural fields. Little is known about diversity of entomopathogenic nematodes in Oklahoma, which is home to 11 ecoregions, nine annual precipitation zones ranging from east to west, and seven soil orders. This study aimed to characterize entomopathogenic nematode communities inhabiting pastureland from different mean annual precipitation zones in Oklahoma. Soil physical parameters and weather data were used to characterize eight pastureland habitats. Soil samples were collected and native entomopathogenic nematodes were isolated using a common bioassay technique. Entomopathogenic nematodes were identified by PCR amplification of individual nuclear ribosomal its regions and sequencing. Six species of Steinernema in the Steinernematidae were isolated, including S. feltiae, S. texanum, S. glaseri., S. carpocapsae, and S. riobrave, and one population of Heterorhabditis bacteriophora in the Heterorhabditidae was recovered. Higher diversity and abundances of entomopathogenic nematodes were found in areas with higher precipitation levels. This study represents the first documentation of these species in OK and indicates a positive correlation between increased entomopathogenic nematodes prevalence as well as diversity and the increase in annual precipitation.

BackgroundThe complex including entomopathogenic nematodes (EPNs) of the genera Steinernema and Heterorhabditis and their mutualistic partner, i.e., Xenorhabdus and Photorhabdus bacteria, respectively possesses many attributes of ideal biological control agents against numerous insect pests as a third partner. Despite authenic opportunities for their practical use as biocontrol agents globally, they are challenged by major impediments especially their cost and reliability.Main bodyThis review article presents major attributes of EPNs to familiarize growers and stakeholders with their careful application. As relatively high EPN costs and frequently low efficacy are still hindering them from reaching broader biopesticide markets, this is to review the latest findings on EPN strain/species enhancement, improvement of production, formulation and application technology, and achieving biological control of insects from the standpoint of facing these challenges. The conditions and practices that affected the use of EPNs for integrated pest management (IPM) are identified. Besides, efforts have been made to address such practices in various ways that grasp their effective approaches, identify research priority areas, and allow refined techniques. Additionally, sampling factors responsible for obtaining more EPN isolates with differential pathogenicity and better adaptation to control specific pest(s) are discussed.ConclusionSpecific improvements of EPN production, formulation, and application technology are reviewed which may help in their broader use. Other diverse factors that optimize EPNs to constitute a cost-effective, value-added approach to IPM are also demonstrated.

Summary The occurrence and diversity of entomopathogenic nematodes (EPN) and their symbiotic bacteria was evaluated in commercial forestry plantations (Eucalyptus spp., Pinus spp. and Acacia mearnsii) and indigenous forests in South Africa. EPN were most prevalent in A. mearnsii plantations, accounting for 60.7% of the isolates, while indigenous forests, plantations of Pinus spp. and Eucalyptus spp. accounted for 35.7, 3.6 and 0% of the isolates, respectively. DNA sequences of the internal transcribed spacer (ITS) and D2-D3 28S rDNA regions were used to identify the nematode species. Four Steinernema spp. were identified, including S. citrae, S. sacchari, two undescribed species, as well as Heterorhabditis bacteriophora and H. baujardi. Heterorhabditis baujardi is reported from South Africa for the first time. Analysis of 16S rRNA of the bacteria confirmed the presence of at least three Xenorhabdus species from Steinernema isolates and two subspecies of Photorhabdus luminescens from Heterorhabditis species.

The present investigation mainly emphasized on the development and use of entomopathogenic nematodes (EPNs) as a bio-insecticide. The success in controlling insect pests in the soil environments increased the production and use of the adapted indigenous EPNs species for insect management in the fields. EPNs as biocontrol agents were capable for high virulence, easy for application, safe for non-target animals and eco-friendly in nature. These nematodes have ubiquitous nature. These occur in low population in their natural habitat which was mass multiplied in the laboratory. In the present investigation, 5 concentrations (30IJs, 60IJs, 90IJs, 120IJs and 150IJs) of Heterorhabditis bacteriophora strain S15 were applied against the 3rd and 4th instar larvae of four major agricultural insect pests, namely Helicoverpa armigera, Spodoptera litura, Agrotis segetum and Mythimna separata under laboratory conditions at different time exposure (24, 48, 72 and 96 hr). It was observed that the 3rd and 4th larval instars of all 4 insects (H. armigera, S. litura, A. segetum and M. separata) were highly susceptible for the pathogenesis caused by H. bacteriophora Sirmaur isolates. Amongst all insects, both the larval instars of M. separata are highly susceptible for EPNs infection with highest 96% and 98% mortality in highest dose @150IJs. In 3rd instar larvae of other insects such as H. armigera, S. litura and A. segetum larval mortality ranges from 84%, 92% and 94% respectively. Among 4th instar larvae of H. armigera, S. litura and A. segetum the pathogenicity varies from 88%, 94% and 96% respectively. The recorded median lethal concentration (LC50) in 3rd instar larvae of H. armigera, S. litura, A. segetum and M. separata varies from 36.15, 30.05, 30.97 and 23.8. Similarly in 4th instar larvae of H. armigera, S. litura, A. segetum and M. separata, LC50 ranged from 31.41, 28.64, 26.92 and 20.64 respectively. Statistically significant variations were observed in the data recorded on the mortality, in all the treatments. EPNs are the best weapon to overcome insect resistance problems and must be employed to manage insect population.

BackgroundThe wheat stink bug, Aelia rostrata Boheman (Hemiptera: Pentatomidae), is one of the harmful insects that caused significant product losses in cereals due to outbreaks. Entomopathogenic nematodes (EPNs) are natural enemies of soil insect pests whose effects as a biocontrol agent against many harmful pests have been demonstrated by many laboratories and field/garden studies in the world. The present laboratory studies, using native EPNs [Steinernema carpocapsae (Black sea isolate), S. feltiae (isolate 09-31) (Aydin isolate) and Heterorhabditis bacteriophora (isolate 09-43) (Aydin isolate)] against the wheat stink bug adults, were carried out.ResultsIn the application of EPNs to the soil in plastic cups, the highest mortality rates (75 and 70%) on wheat stink bug occurred at 200 IJs cm−2 concentration of S. carpocapsae isolate at 15 and 12 °C, respectively. In other tested nematode species, the highest insect mortality was observed at 200 IJs cm−2 concentration of S. feltiae and H. bacteriophora isolates, with mortality rates of 65–35% and 55–25%, at 15 and 12 °C, respectively. S. carpocapsae (Black sea isolate) was the most pathogenic among the three nematodes tested.ConclusionsIt was concluded that S. carpocapsae had the potential as a biocontrol agent against the wheat stink bug, A. rostrata. The applications of S. carpocapsae were the great potential for the management of the pest. Effective use of EPNs should be evaluated in integrated pest management strategies between other biological control agents. According to EPNs laboratory experiments results, field trials should be conducted in future studies.

The increasing cost of nematicides and environmental deterioration are the great challenges to agriculture. Entomopathogenic nematodes (EPNs) could be a choice as biocontrol agent in suppressing the root knot nematode, Meloidogyne incognita on tomato and other crops. A total number of 75 soil samples were collected from different locations of Vehari and Faisalabad, Pakistan. In Vehari out of 14 sites, 13 sites were found positive for EPNs, Nematodes were recovered from 19 (54 %) of 35 soil samples obtained from ecologically diverse habitats. From University of Agriculture Faisalabad, EPNs were recovered from 6 (40 %) of 15 soil samples. While, out of 25 samples collected from Ayub Agriculture Research Institute 9(36%) were found positive for EPNs. Both Steinernema and Heterorhabditis species were found in these locations. The soil samples were also analyzed to indicate the effect of soil texture. Maximum EPNs (36 %) were recovered from sandy loam soil followed by loamy soil. A series of experiments was carried out to unearth EPNs’ soil persistence, reproductive potential and their effects on root knot nematodes. All species and strains of EPNs had potential to persist in almost all type of soils. Persistence was observed in sterilized soil sand and clay (1:1). Maximum persistence was found in S. glaseri (29.11 %) followed by S. pakistanese (28.41 %), H. indica (26.93 %), S. asiaticum (24.42 %), S. feltiae (21.52 %) and H. bacteriophora (21.11 %) which showed the least persistence in sterilized soil. All species of both the families Heterorhabditidae and Steinernematidae did not persist more than 30 % in sterilized soil. Reproductive potential of three EPNs was recorded using the greater wax moth Galleria mellonella larvae. H. indica showed very high reproductive potential within wax moth followed by S. asiaticum and S. pakistanese. On the other hand, maximum emerged infective juveniles per day were recovered from H. indica followed by S. pakistanese and S. asiaticum. Suppressive effect of EPNs against root knot nematodes was observed on susceptible tomato cultivars at different concentration. S. pakistanese suppress M. incognita population more efficiently than H. indica at all the levelsi.e. 1250, 2500 and 5000 nematodes pot-1 . After 35days egg masses (EM) recovered from S. pakistanese treated pots at level 1250 were 232/pot, at level 2500 were 207 and at level 5000 were 135 respectively. Similarly, egg masses recovered from H. indica treated plants at level 1250 were 276, at level 2500 were 212 and at level 5000 were 154 EM pot-1 respectively. No EM were recovered from clean plants on contrary328 EM were recovered from plants with root knot nematodes only.

Chapter 12 - Entomopathogenic Nematodes as Biological Control Agents of Tomato Pests

Potential for the Control ofPlutella xylostellaLarvae with Entomopathogenic Nematodes

This review highlights the latest findings regarding the use of entomopathogenic nematodes against post-harvest insects. Due to their requirements for moisture, entomopathogenic nematodes had received, until lately, limited attention for application to the dry storage environment. Recent improvements of their formulation and application approaches, as well as the discovery of new, more virulent strains have enhanced the efficacy of entomopathogenic nematodes and renewed interest in using entomopathogenic nematodes in the stored-product environment. The nematode species tested against storage insects belong exclusively to the genera Steinernema and Heterhorhabditis. The virulence of entomopathogenic nematodes against post-harvest insects varies depending on the nematode species and strain. Usually, only a single-nematode species or strain is not equally effective against all major stored-product insect pests; therefore, one nematode strain or species cannot be suitable for controlling all species present in the storage environment, where several insect species coexist. The successful application of entomopathogenic nematodes in storage environments for controlling post-harvest insects is highly dependent on several biotic and abiotic factors, such as the host life stage, temperature, and relative humidity. Entomopathogenic nematodes have still to overcome substantial hurdles to become a reliable alternative for commercial applications in warehouses and storage facilities. However, the use of innovative, enhanced methods of formulation and application, such as encapsulation or bait traps, could boost the exploitation of entomopathogenic nematodes in storage facilities against post-harvest insects.

In the Western Cape province of South Africa, codling moth (Cydia pomonella) is the most important lepidopteran pest of apples and pears. Currently an integrated pest management (IPM) strategy is followed. However, chemical control still plays an important role in the control of this pest. Entomopathogenic nematodes (EPNs) of the families Steinernematidae and Heterorhabditidae have been successfully utilized as biological control agents in classical, conservation, and augmentative insect pest management programmes. In this review different biological control options for control of codling moth are considered, with special emphasis on research being done on the biological control of codling moth using EPNs. To integrate nematodes into an IPM system, it is important to conduct research under local environmental conditions for a specific crop. Application of EPNs against codling moth will target the diapausing larval overwintering population above-ground. Especially for commercial application, the unique environmental conditions in the various production areas need to be assessed to allow for the effective use of various EPN species. Orchard application, onto trees poses its own unique challenges with regard to the inundative application of EPNs. Research on the use of EPNs to control codling moth and obstacles encountered in the success of codling moth control are discussed.

Entompathogenic nematodes are found worldwide in a wide array of soil habitats with a broad host range and significant variation in foraging strategies. The primary use of entomopathogenic nematodes (EPNs) in managed plant systems has been focused on inundative releases in a biopesticide strategy. Little effort has been placed in investigating the use of natural occurring or adapted EPN strains for long-term suppression of pest outbreaks in managed systems. This study examined the potential of EPN isolates from Northern New York (NNY), inoculated at a low level (250 million IJ/ha), which are climate adapted and their persistent characteristics preserved to maintain population levels in agricultural fields (N = 82) for multiple years and across crop rotation (alfalfa:corn:alfalfa). Persistence levels for Steinernema carpocapsae (Weiser) (Rhabditida:Steinernematidae) ranged between 8 and 12% of the soil cores assayed in continuous alfalfa and 1-14% of the soil cores assayed in continuous corn rotated from EPN treated alfalfa. Steinernema feltiae (Filipjev) (Rhabditida: Steinernematidae) residual persistence level ranged between 17 and 32% in continuous alfalfa and 22-41% in continuous corn rotated from EPN treated alfalfa. Combined EPN level ranged between 27 and 43% of the soil cores in continuous alfalfa and 28-55% in continuous corn rotated from EPN-treated alfalfa. Inspection of individual fields suggested EPN populations established in prior years at the residual soil core level of 18-35% can respond positively to an increase of susceptible hosts in both alfalfa and corn, often increasing their presence to 100%.

Entomopathogenic nematodes (EPNs) have been identified as being promising biological control agents of key insect pests. The two EPN genera that have shown potential for use as biological control agents within an integrated pest management programme are Steinernema and Heterorhabditis. Large numbers of EPNs can be produced through either in vivo or in vitro culturing practices. Commercialization and the successful use of EPNs to control pests in North America, Australia, Europe and Asia have confirmed the effectiveness of these organisms as biological control agents. Two endemic EPN isolates to South Africa, Heterorhabditis zealandica (SF41) and H. bacteriophora (SF351) have been shown to be effective control agents of codling moth, Cydia pomonella, false codling moth, Thaumatotibia leucotreta, obscure mealybug, Pseudococcus viburni, and the banded fruit weevil, Phlyctinus callosus. Unfortunately, EPNs in large enough numbers for commercial field applications are not yet available on the South African market.

Simple SummaryOnion maggot (Delia antiqua) can be a devastating pest of onion and related crops around the world. While management of this pest typically relies on insecticides to control these pests, growing resistance and desire for alternative control strategies has motivated a search for new methods to manage them effectively. We investigated the potential of using tiny beneficial roundworms called entomopathogenic nematodes to control onion maggots. We conducted surveys in onion-growing areas to see if these nematodes were naturally present, and also tested their compatibility with commonly used insecticides. Our field trials demonstrated that applying entomopathogenic nematodes can significantly reduce the number of onion plants destroyed by onion maggots, leading to higher crop yields. These nematodes could be a useful tool for onion farmers, whether they practice conventional or organic farming. When combined with other strategies like insecticide seed treatments, the use of entomopathogenic nematodes can provide effective control of onion maggots while boosting crop productivity.Onion maggot (Delia antiqua) is a prominent pest of allium crops in temperate zones worldwide. Management of this pest relies on prophylactic insecticide applications at planting that target the first generation. Because effective options are limited, growers are interested in novel tactics such as deployment of entomopathogenic nematodes. We surveyed muck soils where onions are typically grown to determine if entomopathogenic nematode species were present, and then evaluated the compatibility of entomopathogenic nematode species with the insecticides commonly used to manage D. antiqua. We also evaluated the efficacy of these entomopathogenic nematodes for reducing D. antiqua infestations in the field. No endemic entomopathogenic nematodes were detected in surveys of muck fields in New York. Compatibility assays indicated that, although insecticides such as spinosad and, to some extent, cyromazine did cause mortality of entomopathogenic nematodes, these insecticides did not affect infectivity of the entomopathogenic nematodes. Field trials indicated that applications of entomopathogenic nematodes can reduce the percentage of onion plants killed by D. antiqua from 6% to 30%. Entomopathogenic nematodes reduced D. antiqua damage and increased end of season yield over two field seasons. Applications of entomopathogenic nematodes may be a viable option for reducing D. antiqua populations in conventional and organic systems. Together with other management tactics, like insecticide seed treatments, applications of entomopathogenic nematodes can provide a yield boost and a commercially acceptable level of D. antiqua control.

Entomopathogenic fungi and entomopathogenic nematodes are globally distributed soil organisms capable of infecting and killing a vast variety of insects. Therefore, these organisms are frequently used as biocontrol agents in insect pest management. Both entomopathogenic fungi and nematodes share the soil environment and thus can infest and compete for the same insect host; however, natural co-infections are rarely found due to the cryptic soil environment. Our current knowledge on their interactions within hosts mainly comes from laboratory experiments. Because of the recent trend of combining biocontrol agents to increase their efficacy, many studies have focused on the co-application of different species of EPF and EPNs against various insect pests with variable outcomes ranging from synergistic effects and additive effects to antagonism. In addition, the effect on the development and reproduction of each pathogen varies from normal reproduction to exclusion, and generally the outcomes of the interactions are dependent on pathogen and host species, pathogen doses, and the timing of infection. The present review aims to summarize the current knowledge on the interactions of entomopathogenic fungi and nematodes within an insect host and to estimate the possible effects of the interactions on natural pathogen populations and on their use in biocontrol.

The olive fruit fly Bactrocera oleae is one of the most serious and economically damaging insects worldwide, affecting the quality and quantity of both olive oil and table olives. Third instar larvae and pupae of several Tephritidae flies were reported to be susceptible to entomopathogenic nematodes (EPNs), but few studies have been carried out on the olive fruit fly. Laboratory assays were conducted to evaluate the susceptibility of B. oleae larvae and pupae to two commercial EPN species, Steinernema feltiae and Heterorhabditis bacteriophora and two indigenous Italian strains of H. bacteriophora and Steinernema carpocapsae. Moreover, an olive assay in the soil was performed to evaluate the capability of EPN strains to enter inside the olive fruits and interact with B. oleae during the pupal stage or the emergence of adults in the winter diapause. The susceptibility assays with B. oleae were performed in well plates, filled with sterile soil (n = 30 for each EPN strain and insect stage). Adult emergence and mortality were recorded daily for 15 days. Dead pupae and adults were dissected to assess nematode infection. The most noteworthy result was obtained with S. feltiae which was able to infect more than 80% of larvae and it killed the pupae inside olive fruits and the adults during their emergence with the same efficacy. Since this Tephritidae fly spends several months in the soil, the use of EPNs, in particular, S. feltiae may represent a promising method to control this pest.