Entomopathogenic Nematode Species Research Articles

Isolation, identification of entomopathogenic nematodes with insights into their distribution in the Syrian coast regions and virulence against Tuta absoluta.

The occurrence and distribution of entomopathogenic nematodes (EPNs) in the Syrian coast regions remain relatively uncharted. To address this gap in our knowledge, an extensive survey of these ecosystems was essential. This study aims to isolate and identify EPNs from diverse ecosystems within the coastal regions. The distribution of EPNs in cultivated and natural environments was analyzed according to habitat, altitude, and sampling season factors. Between 2017 and 2020, EPNs were recovered from 27 out of 821 soil samples (3.28%) and collected from 24 out of 375 sampling sites (6.4%). Based on morphological, morphometric, and molecular (ITS) characteristics, four EPN species were identified: Heterorhabditis indica (51.85%), representing the first report of its occurrence in the coastal regions, H. bacteriophora (33.33%), H. pakistanense (7.4%), which is also reported for the first time in Syria, and Steinernema affine (7.4%). There were statistical differences in the abundance and recovery frequency of EPNs in each type of habitat. Additionally, there were statistical differences in the altitude and sampling season recovery frequency. Co-inertia analysis revealed correlation between the distribution and occurrence of EPNs in vegetation habitats, altitude, and sampling seasons, as well as some soil characteristics. H. indica and H. bacteriophora were associated with citrus orchards, low-altitude ranges, moderate organic matter, and acidic soil. More specifically, H. indica isolates were correlated with olive orchards, vegetable fields, autumn season, and clay, sandy, and sandy loam soils. Meanwhile, H. bacteriophora isolates were correlated with tobacco fields, grasslands, alkaline pH, spring season, silty loam, and clay loam soils. H. pakistanense was linked to pear orchards, vineyards, moderate pH, and low organic matter. S. affine occurred in walnut orchards, silty soil, higher altitudes, and winter season. The virulence levels of three native EPN isolates (S. affine, H. indica and H. bacteriophora) were evaluated against 3rd and 4th instar larvae (outside and inside mines) and pupae of T. absoluta, a destructive pest in Syria. All three native EPN species exhibited ability to infect and kill the insect, with observed significant differences in their virulence. This study provides an understanding of EPN occurrence, distribution, and their potential for application in sustainable pest control strategies in Syria.

Multigene Sequence-Based and Phenotypic Characterization Reveals the Occurrence of a Novel Entomopathogenic Nematode Species, Steinernema anantnagense n. sp.

Three entomopathogenic nematode populations were isolated from agricultural fields in the Anantnag district of Jammu and Kashmir (India). Sequences of multiple gene regions and phenotypic features show that they are conspecific and represent a novel species. Molecular and morphological features provided evidence for placing the new species into the "Kushidai" clade. Within this clade, analysis of sequence data of the internal transcribed spacer (ITS) gene, the D2D3 region of the 28S rRNA gene, the mitochondrial cytochrome oxidase I (mtCOI) gene, and the mitochondrial 12S (mt12S) gene depicted the novel species as a distinctive entity closely related to Steinernema akhursti, S. kushidai, and S. populi. Phylogenetic analyses also show that the new species is a sister species to S. akhursti, and these two species are closely related to S. kushidai and S. populi. Additionally, the new species does not mate or produce fertile progeny with any of the closely related species, reinforcing its uniqueness from a biological species concept standpoint. The new species is further characterized by the third-stage infective juveniles with almost straight bodies (0.7-0.8 mm length), poorly developed stoma and pharynx, and conoid-elongate tail (49-66 µm) with hyaline posterior part. Adult females are characterized by short and conoid tails bearing a short mucron in the first generation and long conoid tails with thin mucron in the second generation. Adult males have ventrally curved spicules in both generations. Moreover, the first-generation male has rounded manubrium, fusiform gubernaculum, conoid and slightly ventrally curved tails with minute mucron, and the second generation has rhomboid manubrium anteriorly ventrad bent, and tails with long and robust mucron. The morphological, morphometrical, molecular, and phylogenetic analyses support the new species status of this nematode, which is hereby described as Steinernema anantnagense n. sp. The bacterial symbiont associated with S. anantnagense n. sp. represents a novel species, closely related to Xenorhabdus japonica. These findings shed light on the diversity of entomopathogenic nematodes and their symbiotic bacteria, providing valuable information for future studies in this field.

Steinernema carpocapsae

Steinernema and Heterorhabditis are not closely related phylogenetically but they share many characteristics via convergent evolution. Over 100 species of Steinernema have been described. Here we focus on Steinernema carpocapsae. All entomopathogenic nematode (EPN) species are symbiotically associated with entomopathogenic bacteria: S. carpocapsae retains Xenorhabdus nematophila. The bacteria kill the insect host along with EPN-produced factors, provide nutrition for the EPNs, and produce metabolites that protect the infection by inhibiting opportunistic colonization by other soil organisms. S. carpocapsae is a common species isolated from soil from every continent except Antarctica and was the first EPN-produced in vitro and commercially developed for pest control. To date, 12 species of EPNs have been commercialized for biological control of soil insect pests for agriculture, municipalities, and homeowners.

Assessment of biocontrol potential of different Steinernema species and their bacterial symbionts, Xenorhabdus species against larvae of almond moth, Ephestia cautella (Walker)

The almond moth, Ephestia cautella is a serious pest of stored food commodities including dried figs, dates, raisins, cocoa beans. The control of E. cautella infestations in storage that mostly relies on toxic insecticides or fumigants has caused emergence of resistant pest populations as well as residues on the commodities. Entomopathogenic nematodes (EPNs) and their endosymbionts are one of the emerging approaches in eco-friendly pest management and pose no health risk to humans and the environment. Therefore, here we evaluated the toxicity of different EPN species (Steinernema feltiae, S. carpocapsae, and S. bicornotum) and their endosymbiotic bacteria (Xenorhabdus nematophila, X. bovienii, and X. budapestensis) on the 3rd and 4th instars larvae of E. cautella under controlled conditions. The IJs of EPNs were applied to concrete arenas in Petri dishes at three concentrations (50, 100, and 200 IJs/cm2). Oral and contact toxicity of the cell-free supernatants and cell suspension of symbiotic bacteria (4x107 cells/mL) were tested against both larval instars of E. cautella. Steinernema carpocapsae and S. feltiae induced mortalities over 80% at their lowest concentrations against both larval instars after 24 h of application. Oral and contact treatments of cell-free supernatants and cell suspensions were lethal for both larval instars; however, higher mortalities were generally obtained from direct exposure of larvae to cell-free supernatants and cell suspensions. The contact treatment of X. nematophila exhibited the highest virulence, causing 70 and 82.5% mortalities in 3rd and 4th instar larvae after 72 h of application, respectively. The anti-feedant activity of cell-free supernatants and cell suspensions was also observed in both instars in oral treatments. The findings of this study suggest that EPNs and their symbiotic bacteria have enormous potential for the eco-friendly control of E. cautella.

Natural infection of white grubs (Coleoptera: Scarabaeidae) with entomopathogenic nematodes in the KwaZulu-Natal province of South Africa.

White grubs are root feeding larvae of beetles (Coleoptera: Scarabaeidae) that are sporadic pests in agriculture and can lead to economic damage. The grubs feed on the roots of plants, while the adult beetle can bore into underground stems, as well as cause defoliation of plants. Sporadic incidence of larvae with symptoms of nematode infections were detected in wattle and sugarcane plantations in the KwaZulu-Natal province of South Africa. The larvae with infection symptoms were isolated, washed, and put on water traps to collect infective juveniles of possible nematode infections. Three species of entomopathogenic nematodes (EPNs) were isolated from the white grub larvae. These included Steinernema bertusi isolated from Maladera sp. 4., Oscheius myriophila from Maladera sp. 4 and Schizonchya affinis, and Steinernema fabii isolated from Maladera sp. 4., Pegylis sommeri, and S. affinis. Of these S. fabii was the most common species in the sample (87%). This is the first report of such a high diversity of locally occurring EPNs found naturally associated with white grub species in this region of South Africa.

Spreyleme ve Toprak Enjeksiyonu Yöntemleri ile Toprağa Uygulanan Entomopatojen Nematodların Şeftali Bahçesinde Kalıcılığının Belirlenmesi

Entomopathogenic nematodes (EPN) are effective biological control agents against underground and cryptic pests. Persistency and survival of EPN in soil after soil application is important for long term success of management programs. In this study, it was aimed to determine the soil persistency of 4 native EPN species after surface spraying and soil injection applications in a peach orchard. In the study, S. feltiae (96), S. carpocapsae 1133, H. bacteriophora 1144 and S. affine 47 species were applied in 30 l water with 140.000 IJ/tree dose per tree by surface spraying and soil injection methods. EPN were applied to soil with a watering can in surface spraying method and with a pulverizator into 5-15 cm depth in soil injection method. After the monthly application, soil samples were collected and EPN presence was tested with G. mellonella larvae and White traps in the laboratory. The study was conducted for 2 times in 2018 and 2019. At the end of the study, EPN persistency in soil was found to be 90 days in 2018 and 150 days in 2019.

Potential of Entomopathogenic Nematode HbSD as a Candidate Biocontrol Agent against Spodoptera frugiperda.

Spodoptera frugiperda is a highly destructive and polyphagous pest that causes severe damage to various crops, especially maize. The wide use of chemical insecticides to control S. frugiperda results in resistance against commonly used chemicals and resistant mutations will expand in populations accompanied by a spread to vulnerable areas. Consequently, more effective and friendly strategies must be explored to minimize losses caused by S. frugiperda. Entomopathogenic nematodes (EPN) are good candidates for the biological control of different species of insect pests, including S. frugiperda. In the current study, the infective capabilities of the EPN species HbSD, belonging to Hetrerorhabditis bacteriophora, were evaluated against S. frugiperda under laboratory, greenhouse and field conditions. In laboratory assays, HbSD was highly virulent against 3rd/5th instar larvae, which was related to HbSD concentration and exposure durations. In greenhouse assays, spraying aqueous HbSD also showed good performance in killing larvae on maize leaves. However, the virulence of HbSD decreased in field trials where many adverse factors affecting survival and efficacy were encountered by HbSD. Overall, our study provides an alternative EPN for the biological control of S. frugiperda with the potential to be developed as a sustainable option for efficient pest management.

Evaluation of Indigenous Strains of Entomopathogenic Nematodes, in Combination with Low-Toxicity Insecticides at Low and High Dosages South American Tomato Pinworm, Tuta absoluta (Meyrick) (Lepidoptera, Gelechiidae)

The laboratories experiments were conducted during September, 2021 to test the pathogenicity of two EPNs species S. feltiae and H. bacteriophora at different (IJs cm-2) concentrations against Tuta absoluta (Meyrick)(Lepidoptera, Gelechiidae). The experimental location in Department of Entomology, Nematology Laboratory, Dr. Yashwant Singh Parmar University of Horticulture and Forestry, Solan, Himachal Pradesh, India. The native isolate was obtained from soil samples, collected from survey was carried out in Mid-hills of the North Himalayas, India, to investigate the diversity and frequency of entomopathogenic nematodes (EPNs). Our objective was to evaluate the efficacy of S. feltiae (HR1) and H. bacteriophora (HR2) in combination with low-toxicity insecticides at low and high dosages to control final-instar larvae in bioassays. The use of S. feltiae+Spinosad or chlorantraniliprole caused larvae mortality of over 100% at 96 h and second bioagent H. bacteriophora+Spinosad and chlorantraniliprole mortality of over 97.50% at 96 h at the high dose and should be included as a least toxic strategy to control T. absoluta. Our results showed that T. absoluta were suitable hosts for local indigenous strains performed good potential for biological control against invasive species. In combination with low-toxicity insecticides at low and high dosages to control final-instar larvae mortality of over 100% at 96 h at the high dose and should be included as a least toxic strategy to control tomato pinworm.

Direct antagonistic effect of entomopathogenic nematodes and their symbiotic bacteria on root-knot nematodes migration toward tomato roots

AimsNegative interactions in the rhizosphere between entomopathogenic nematodes (EPNs) and plant-parasitic nematodes, such as root-knot nematodes (RKNs), have been documented over the past two decades but the mechanisms and dynamics of such interactions remain largely elusive.MethodsHere, we evaluated the effect of the inoculation position of two EPN species, Steinernema feltiae and Heterorhabditis bacteriophora, as well as different facets of the EPN-bacterial symbiont complex on the migration of RKNs toward tomato roots, both in sand and in Pluronic gel conditions.ResultsWhen EPNs were placed between the position of the RKNs and the roots, the movement of RKNs toward the roots was inhibited. We observed this same pattern both in sand and in Pluronic F-127 (PF-127) gel for two species of EPNs. We also observed that different components of the EPNs/bacterial symbiont complex (bacteria separate from the nematodes vs. the nematode-bacterium complex), and particularly the cell-free supernatant produced by the bacterial culture, displayed inhibitory effects on RKNs.ConclusionTherefore, the EPNs/bacterial complex, by slowing down the movement of RKNs toward the host plant roots, could partially contribute to RKN control. By screening for the most repulsive strains of EPNs that are also effective against insect pests, the combined target approach should alleviate EPNs application costs in integrated pest management practices.

Sustainable Grain Protectants: Recruiting Entomopathogenic Nematodes against Stored-Product Coleopterans

Stored-product commodities are attacked by numerous insect species. The adulticidal effects of entomopathogenic nematodes (EPNs) on grains remain uninvestigated. Thus, in the current study, seven doses of the EPNs Heterorhabditis bacteriophora Poinar (Rhabditida: Heterorhabditidae), Steinernema carpocapsae (Weiser) (Rhabditida: Steinernematidae), and Steinernema feltiae (Filipjev) (Rhabditida: Steinernematidae) were inoculated on wheat kernels against adults of Trogoderma granarium Everts (Coleoptera: Dermestidae), Tenebrio molitor L. (Coleoptera: Tenebrionidae), and Alphitobius diaperinus (Panzer) (Coleoptera: Tenebrionidae). Complete mortality (100.0%) of T. granarium was recorded after exposure for eight days to the highest dose of 50,000 Infective Juveniles/mL (IJs/mL) of all tested EPN species. At the same exposure interval, 62.2%, 85.6%, and 76.7% of T. molitor were killed by 50,000 IJs/mL of H. bacteriophora, S. carpocapsae, and S. feltiae, respectively. The highest mortality of A. diaperinus (11.1%) was documented eight days post-exposure to 50,000 IJs/mL of H. bacteriophora. In general, T. granarium was highly susceptible, followed by T. molitor and A. diaperinus. Concerning EPN species, S. carpocapsae exhibited the highest insecticidal capacity, followed by S. feltiae and H. bacteriophora. Trogoderma granarium and T. molitor can be sufficiently managed by the highest dose of 50,000 IJs/mL of all three EPNs and by S. carpocapsae, respectively. However, A. diaperinus was not affected by any EPNs.

Long-term storage does not affect the infectivity of entomopathogenic nematodes on insect hosts.

Entomopathogenic nematodes (EPNs) are effective biopesticides used in insect control. There are several formulations of entomopathogenic nematodes which are commercially available, but their popularity is low because the requirement of periodic release of stored entomopathogenic nematodes in field has reduced infectivity and is a constraint in large-scale repeated application of entomopathogenic nematodes in field. So, in order to overcome this impediment, the current study focuses on storage of entomopathogenic nematodes for a longer period of time using encapsulating beads. In this study, three EPNs, namely, Steinernema carpocapsae, Steinernema monticolum, and Rhabditis blumi, were encapsulated with Arabic gum and sodium alginate gel beads at different concentrations. Bio-efficacy of stored EPNs at different concentrations (50, 100, 200, 500, and 1000 infective juveniles (IJs)) in varying time intervals of 3, 6, 9, and 12weeks were tested against Culex quinquefasciatus larvae. The results show that, after 3weeks of storage, these entomopathogenic nematode species showed survival up to 96%, and in 12-week storage, survival rate was 50%. The virulence of the progeny that emerged from these stored entomopathogenic nematodes was similar to the fresh infective juveniles. The results of the present study show that Arabic gum-sodium alginate combination is a promising approach toward storing entomopathogenic nematodes. Furthermore, semi-field trials showed 70-90% larval mortality at a concentration of 3000 IJs (encapsulated and stored entomopathogenic nematodes in S. monticolum, S. carpocapsae, and R. blumi) on C. quinquefasciatus larvae. KEY POINTS: • Increased survival of stored EPNs (S. carpocapsae, S. monticolum, and R. blumi) in encapsulated gel using Arabic gum, sodium alginate, and yeast cells was assessed. • The efficacy was greater in stored EPNs at different concentrations from 3 to 12 weeks. • Semi-field trials of stored encapsulated EPNs are efficient in mosquito larval control.

A Review on role of Entomopathogenic nematodes in integrated pest management

Entomopathogenic nematodes (EPNs), which are microbial pathogens cum insect pest’s biocontrol agents, have been used successfully in agricultural systems. They may be easily cultivated in vivo or in vitro and are extremely pathogenic, quickly killing their hosts. Due to their widespread production in liquid media, their production costs have recently decreased dramatically, while still being safe for the environment and non-target vertebrates. Additionally, there are no challenges in using EPNs because they can be coupled with practically all chemical control chemicals and are simple to spray using ordinary equipment. EPNs are frequently used to control economically significant insect pests in a variety of farming systems, including nurseries, greenhouses, turf grass, and fruit orchards. Only in the early 1980’s did EPNs start to be used for biocontrol, and this needed a gradual advancement of both science and technology. The commercialization of nematode-based insect pest management was greatly aided by the nematode's mass production. This review paper discusses different species of EPNs, its Mass production and utilization in Integrated Pest Management program.

Identification and Biocontrol Potential of Entomopathogenic Nematodes and Their Endosymbiotic Bacteria in Apple Orchards against the Codling Moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae).

The codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), is one of the major pests in pome fruit production worldwide. Heavy treatment of the larvae of C. pomonella with insecticides triggered the development of resistance to many groups of insecticides. In addition, the increasing concern about the adverse effects of synthetic insecticides on human health and the environment has led to the development of sustainable and eco-friendly control practices for C. pomonella. The entomopathogenic nematodes (EPNs) (Steinernema and Heterorhabditis spp.) and their endosymbionts (Xenorhabdus and Photorhabdus spp.) represent a newly emerging approach to controlling a wide range of insect pests. In the present study, field surveys were conducted in apple orchards to isolate and identify EPNs and their endosymbionts and evaluate their insecticidal efficacy on the larvae of C. pomonella. EPNs were isolated from 12 of 100 soil samples (12%). Seven samples were identified as Steinernema feltiae (Filipjev, 1934) (Rhabditida: Steinernematidae), whereas five samples were assigned to Heterorhabditis bacteriophora (Poinar, 1976) (Rhabditida: Heterorhabditidae). The pathogenicity of the EPN species/isolates was screened on the last instar larvae of G. mellonella. The two most pathogenic isolates from each EPN species were tested against fifth instar larvae of C. pomonella under controlled conditions. The maximum mortality (100%) was achieved by all EPN species/isolates at a concentration of 100 IJs/larva 96 h after treatment. The endosymbionts of selected H. bacteriophora and S. feltiae species were identified as Photorhabdus luminescens subsp. kayaii and Xenorhabdus bovienii, respectively. The mortality rates ranged between 25 and 62% when the fifth larval instar larvae of C. pomonella were exposed to the treatment of cell-free supernatants of symbiotic bacteria. In essence, the present survey indicated that EPNs and their symbiotic bacteria have good potential for biological control of C. pomonella.

Entomopathogenic nematodes for the control of oriental fruit fly Bacterocera dorsalis (Diptera: Tephritidae)

BackgroundFruit fly species are most damaging pests around the globe which reduced the commercial value of fruits at maturity. Entomopathogenic nematodes (EPNs) from genera Heterorhabditis and Steinernema cause death by inducing septicimia in insect pests in the soil, moreover, endemic nearly all soils. Current study was planned to manage the oriental fruit fly, Bacterocera dorsalis (Hendel.) (Diptera: Tephritidae) hazards by using indigenous EPNs (Heterorhabditis bacteriophora, H. indica, Steinernema asiticum, S. corpocapsae and S. glasseri) as they have host finding ability and recognise as potential eco-friendly biocontrol agent over synthetic chemicals. MethodsStudy for the assessment of EPNs concentrations, various temperatures, soil type and soil moisture levels against mortality (%) of fruit fly (B. dorsalis) larvae was conducted in completely randomized design (CRD) under factorial arrangements. ResultsEPNs concentrations (70 IJs/ml, 110 IJs/ml, 150 IJs/ml) showed that S. asiaticum (150 IJs/ml) showed maximum mortality (94.97 %) of B. dorsalis as compared to other used EPNs along with their respective concentrations. Impact of various temperatures (20 °C, 24 °C, 28 °C, 32 °C, 36 °C) with respect to used EPNs exhibited that H. indica (36 °C) showed maximum mortality (94.33 %) of B. dorsalis as compared to all other treatment. Various soil types (Sandy, Sandy loam, Loam, Clay) impacted the infectivity of EPNs against fruit fly, In case of sandy loam soil, S. asiaticum showed maximum mortality (98.05 %) of B. dorsalis followed by all used treatments. Soil moisture level (12 %, 18 %, 24 %, 30 %) also significantly influenced the infectivity of EPNs against mortality of fruit fly. In case of 12% moisture level, S. asiaticum showed maximum mortality (99.06 %) of B. dorsalis over all the applied treatments along with respective moisture levels. ConclusionIn crux, Steinernema asiaticum higher concentration exhibited efficient control of fruit fly larvae in sandy loam soil with 12 % moisture level at 36 °C over the used EPN species. While application of EPNs against fruit fly is most suitable strategy to manage the fruit fly hazards and it should be included as a part of integrated pest management control programme.

Effect of temperature on survival of Australian entomopathogenic nematodes and their virulence against the Queensland fruit fly, Bactrocera tryoni

Entomopathogenic nematodes (EPNs) are commonly used biocontrol agents of insect pests, with a wide range of commercially available isolates targeting specific pests. New isolates are, however, required to improve pest control across a wider range of environmental conditions for target pests, including emerging threats. We assessed the effect of temperature on survival and virulence of 17 Australian isolates of five EPN species (Heterorhabditis bacteriophora, Heterorhabditis indica, Heterorhabditis marelatus, Heterorhabditis zealandica and Steinernema feltiae) against larvae and pupae of the Queensland fruit fly, Bactrocera tryoni. All isolates still infected and killed larvae after infective juveniles (IJ) had been kept without insect hosts at 15 °C, 25 °C or 30 °C for two weeks, indicating their potential to remain viable under field conditions. However, the mean LD50 value ranged from 35 to 150 and was generally lower at 15 °C than at 25 °C and 30 °C. Similarly, after IJs had been kept at 25 °C for 1–3 weeks without insect hosts, all isolates infected B. tryoni larvae, with mean LD50 values ranging from 25 to 144. Interestingly, 15 isolates infected and killed B. tryoni pupae after one week, with a mean LD50 value between 130 and 209, but only two isolates after two weeks, with a mean LD50 value between 229 to 209. No pupal mortality was seen after three weeks. In absence of hosts, EPNs survived longer at 15 °C and 25 °C than at 30 °C. Complete EPN mortality occurred after nine weeks at 30 °C, and after 18 weeks at 15 °C and 25 °C, except for some survival in one S. feltiae isolate (Sf.ECCS). Overall, six isolates of H. indica (Hi.HRN2, Hi.LMI2, Hi.QF6), H. bacteriophora (Hb.HIE), H. zealandica (Hz.NAR1) and S. feltiae (Sf.ECCS) performed best and need further testing as potential biocontrol agents against B. tryoni under semi-field and field conditions.

Laboratory and field trials reveal the potential of a gel formulation of entomopathogenic nematodes for the biological control of fall armyworm caterpillars (Spodoptera frugiperda)

The fall armyworm (FAW), Spodoptera frugiperda Smith (Lepidoptera: Noctuidae) can cause tremendous yield losses in maize. Its invasion into Africa and Asia has dramatically increased the use of insecticides in maize agro-ecosystems. Safe, effective and readily available alternatives are urgently needed. Entomopathogenic nematodes (EPN) represent a promising and sustainable option to control fall armyworm caterpillars on maize. Commonly used against soil insect pests, EPN can also be applied to control above-ground pests if formulated appropriately. We explored the possibility to control FAW by incorporating the EPN species Steinernema carpocapsae into protective formulations that can be easily applied into the whorl of maize plants, where the caterpillars mostly feed. We tested this approach in laboratory cage experiments as well as in field trials. In the laboratory, treating maize plants with a low dose of S. carpocapsae (3000 infective juveniles per plant) formulated in a carboxymethyl cellulose (CMC) gel caused 100% mortality of FAW caterpillars and substantially reduced plant damage, whereas EPN applied in water or a surfactant-polymer-formulation (SPF) caused 72% and 94% mortality, respectively. Under field conditions, one-time treatments with S. carpocapsae applied in water, SPF or CMC decreased plant damage, but only the EPN-gel formulation significantly reduced FAW infestation. As compared to control, about 40% fewer caterpillars were found on plants treated with EPN formulated in the gel. Notably, the EPN-gel formulation was as effective as a standard dose of cypermethrin, a pyrethroid insecticide commonly used against FAW, in reducing FAW infestation. Repeated applications may be needed to reduce re-infestations by FAW across a whole cropping season depending on the local maize phenology and pest dynamics. These findings demonstrate that EPN, when properly formulated, are excellent candidates for the biological control of FAW, and can be a safe and sustainable alternative to synthetic insecticides.

Low-temperature exposure has immediate and lasting effects on the stress tolerance, chemotaxis and proteome of entomopathogenic nematodes.

Temperature is one of the most important factors affecting soil organisms, including the infective stages of parasites and entomopathogenic nematodes, which are important biological control agents. We investigated the response of 2 species of entomopathogenic nematodes to different storage regimes: cold (9°C), culture temperature (20°C) and temperature swapped from 9 to 20°C. For Steinernema carpocapsae, cold storage had profound effects on chemotaxis, stress tolerance and protein expression that were retained in temperature-swapped individuals. These effects included reversal of chemotactic response for 3 (prenol, methyl salicylate and hexanol) of the 4 chemicals tested, and enhanced tolerance to freezing (−10°C) and desiccation (75% RH). Label-free quantitative proteomics showed that cold storage induced widespread changes in S. carpocapsae, including an increase in heat-shock proteins and late embryogenesis abundant proteins. For Heterorhabditis megidis, cold storage had a less dramatic effect on chemotaxis (as previously shown for proteomic expression) and changes were not maintained on return to 20°C. Thus, cold temperature exposure has significant effects on entomopathogenic nematodes, but the nature of the change depends on the species. Steinernema carpocapsae, in particular, displays significant plasticity, and its behaviour and stress tolerance may be manipulated by brief exposure to low temperatures, with implications for its use as a biological control agent.

Insecticidal activities of the local entomopathogenic nematodes and cell-free supernatants from their symbiotic bacteria against the larvae of fall webworm, Hyphantriacunea

The fall webworm (FWW), Hyphantria cunea Drury (Lepidoptera: Erebidae), is an invasive and polyphagous insect pest of many economically important crops such as hazelnuts, apple, and mulberry. Recently, there have been an increasing number of reports about the damaging activities of FWW from hazelnut growing areas of Turkey indicating that currently existing control methods fail to satisfy the expectations of growers. Entomopathogenic nematodes (EPNs) in the Steinernematidae and Heterorhabditidae (Nematoda: Rhabditida) families and the symbiotic bacteria they carry in their intestine have a great potential for the management of many agriculturally important pests. In this study, the symbiotic bacteria of local EPN species (Heterorhabditis bacteriophora AVB-15, Steinernema feltiae KCS-4S, and Steinernema bicornotum MGZ-4S) recovered from the central Anatolia region was characterized using recA gene region as Photorhabdus luminescens, Xenorhabdus bovienii and Xenorhabdus budapestensis. The contact (25, 50, 100, 200 IJs/Petri) and oral efficacies of the infective juveniles (IJs) (25, 50, 100, 200 IJs/leaf) of these EPN isolates determined on 3rd/4th instar larvae, and cell-free supernatants from the identified symbiotic bacteria were evaluated separately on the 3rd and 4th larval instars of FWW in Petri dish environment under laboratory conditions (25 ± 1 °C, 60% of RH). In the Petri dish bioassays of EPN species, the most pathogenic isolate at the 1st DAT and 4th DAT was S. feltiae which caused 50% mortality at the highest concentration (200 IJs/Petri) and the highest mortality rate (97.5%) were achieved at 4th DAT by H. bacteriophora AVB-15 isolate. Surprisingly, the mortality rates were generally higher at the lowest concentrations and 82.5% mortality were reached 4th DAT by S. bicornotum at the lowest concentration (25 IJs/leaf) in the leaf bioassays. Mortality rates were higher in both Petri dish and filter paper efficacies of cell-free supernatants at the 2nd DAT and the highest mortality (87.5%) was reached in the contact efficacy studies when applied X. bovienii KCS-4S strain. The results suggest that the tested EPN species and CFSs have good potential for biological control of the larvae of FWW and can contribute to the IPM programs of FWW. However, the efficacy of both IJs of EPNs and CFSs of their symbiotic bacteria on larvae of FWW requires further studies to verify their efficiency in the field.

Evaluation of Entomopathogenic Nematodes against Red Palm Weevil, Rhynchophorus ferrugineus (Olivier) (Coleoptera: Curculionidae).

Simple SummaryThe red palm weevil is considered the most notorious pest for different species of palms around the globe. Due to the concealed nature of the red palm weevil, the use of biocontrol agents, especially EPNs, is considered most effective. Among biocontrol agents, entomopathogenic nematodes provide effective control of the different developmental stages of the red palm weevil. In the current investigation, the infective capabilities of four different species of entomopathogenic nematodes were investigated against larvae (5th and 6th instars), pupae enclosed in their cocoons, and adult red palm weevil (newly formed), under laboratory and field conditions. Our results indicated that the S. carpocapsae and H. bacteriophora were the most effective EPN species against different developmental stages of the red palm weevil under laboratory as well as field conditions. The larval stage of the red palm weevil was found to be the most susceptible to infection by EPNs compared with pupal and adult stages. From the present findings, we can infer that S. carpocapsae and H. bacteriophora are the most effective EPN strains and recommend their use in the sustainable management of the red palm weevil.Entomopathogenic nematodes play a pivotal role as biocontrol agents for different species of insect pests, including the red palm weevil. In the current investigation, the infective capabilities of four species of entomopathogenic nematodes, including Hetrerorhabditis bacteriophora, Steinernema feltiae, Steinernema glaseri, and Steinernema carpocapsae, were evaluated against larvae, pupae, and adult red palm weevil under laboratory and field conditions. The pathogenic potential of selected nematode species was assessed based on dissection and adult emergence of weevils. Our results indicated that S. carpocapsae and H. bacteriophora, with a respective 94.68 and 92.68% infection rate, were the most effective EPN species against red palm weevil larvae. Focusing on adult emergence, the aforementioned EPNs were comparatively less pathogenic and resulted in 63.60 and 60.20% infested pupae, respectively. It is noted that adult emergence is the better option to evaluate the pathogenic potential of EPNs, compared with the dissection of insects. The S. carpocapsae was found to be most effective against the 6th instar larvae of the red palm weevil and caused 100% mortality at 240 h after treatment. On the other hand, S. glaseri and S. feltiae were found to be the least pathogenic and caused 70 and 76% mortality, respectively. All of the evaluated nematode species were found to be highly infective under field conditions. The S. carpocapsae was found to be the most pathogenic, causing 83.60% mortality of the red palm weevil. However, the tested nematodes were found most effective against larvae, followed by adult weevils, but their effect was minimal against the pupae of red palm weevils. Based on these findings, we conclude that the S. carpocapsae and H. bacteriophora could be used as a sustainable option for the efficient management of the red palm weevil.

Influence of entomopathogenic nematodes, symbiotic bacteria and ascarosides on the dispersal behaviour of Meloidogyne incognita

Summary Dispersal is an important behaviour for nematodes. Entomopathogenic nematodes (EPN) are able to regulate plant-parasitic nematodes in the field. However, the mechanism for the interactions between two types of nematodes is not clearly known. The effects of 12 synthesised ascarosides, three EPN species (Steinernema carpocapsae All, Heterorhabditis bacteriophora H06 and H. indica LN2), and 15 symbiotic bacterial isolates from EPN on the dispersal of Meloidogyne incognita were investigated. The results revealed that M. incognita juveniles were repelled, to various degrees, by most of the tested ascarosides (especially ascr#9), three species of EPN, and by bacterial isolates (especially TT01 from H. bacteriophora TT01 and H06 from H. bacteriophora H06), compared with the controls. Ascr#9 was abundant in M. incognita juvenile-conditioned supernatant. This provides useful cues for elucidating the interaction mechanism between two nematode groups and establishing alternative techniques for the safe and effective control of root-knot nematodes.