Entomopathogenic Nematodes Isolates Research Articles

Evaluation of cell-free supernatants from the symbiotic bacteria of entomopathogenic nematodes for controlling the colorado potato beetle [Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae)]

The Colorado potato beetle (CPB), Leptinotarsa decemlineata, poses a significant threat to potato crops globally and has developed resistance to numerous insecticides. Entomopathogenic nematodes (EPNs), from the genera Steinernema and Heterorhabditis, are promising biocontrol agents. This study aimed to identify the bacterial symbionts of ten native EPN isolates, evaluate the efficiency of cell free supernatants (CFSs) from their symbiotic bacteria against different developmental stages of CPB, and determine the effect of these CFSs on CPB developmental stages and lifespan. The recA gene region was utilized to determine the symbiotic bacteria of ten local EPNs. CFSs from these bacteria were applied orally and through contact to CPB’s various developmental stages (L1/L2, L3/L4 larval stages, and adults). Mortalities, developmental transition times, and lifespans of adults were observed. The CFSs showed significant toxicity to CPB, with higher efficiency against young larvae. The CFSs exhibited cumulatively lethal effects over time, particularly on L1/L2 larval stages. CFSs from X. bovienii exhibited the highest efficacy. In all cases, where larvae received CFSs orally or by contact, they failed to develop into pupae and adults. In contrast, the transition periods of old larvae to pupal and adult stages were comparable to those of the control group. Lifespans of adults differed based on bacterial isolates and application methods. This study shows the potential efficacy of CFSs from Xenorhabdus and Photorhabdus as biocontrol agents against CPB, particularly in its young larval stages. Further research is needed to unravel the mechanisms behind these effects and examine the impact on CPB mating and oviposition behaviors.

Biocontrol potential of entomopathogenic nematodes against camel tick, Hyalomma dromedarii (Acari: Ixodidae)

Entomopathogenic nematodes (EPNs) are a well-established biocontrol agent for insect pests. Using such a bio-agent to eliminate ticks has only been reported in a few cases. The current study intended to determine how the camel tick, Hyalomma dromedarii Koch, 1844 (Acari:Ixodidae), engorged female, was affected by various concentrations and timing of exposure to infected juveniles of five EPN isolates from two species. The six groups of engorged females, each with 25 ticks, were subjected to five concentrations of 50, 100, 150, 300, and 600 infective juveniles (IJs)/female in order to perform the work. Female mortality was observed every day for up to 72 h. The groups' average weights were statistically equivalent. The following biological parameters: initial weight of the female (mg); pre- and oviposition periods (days); survival period (days); initial weight of the egg mass (mg); hatching percentage (%H); nutritional efficacy index (NEI); and the control efficacy (%) of the engorged females as influenced by Heterorhabditis indica NEM-23 and H. bacteriophora NEM-26 infections were also measured. The results showed a linear increment in female mortality with the increase in EPN concentrations. Three days after being exposed to H. bacteriophora at 300 or 600 IJs/Female, all H. dromedarii individuals died, while the group containing 50 IJs/Female of the same EPN reached 75 %. All biological parameters were altered by EPNs, and there were extremely noticeable variations between the concentrations and the untreated group. These findings indicate that both Heterorhabditis isolates acted negatively on the parameters that were being observed, encouraging one to believe that this EPN was effective in controlling engorged females of H. dromedarii in the laboratory.

Bazı entomopatojen nematodların etkinliğinde kuraklığın rolü

Entomopathogenic nematodes (EPNs) are endoparasitic organisms commonly used in the control of agricultural pests. There are several factors that determine the efficacy of EPNs on hosts, with one of the most significant being soil moisture. The aim of this study is to determine the effectiveness of some EPNs on hosts at different doses and under different soil moisture conditions. The study utilized 1 Hybrid Strain and 3 EPN isolates, Heterorhabditis bacteriophora Poinar, 1976 (Rhabditida: Heterorhabditidae) HBH hybrid strain, Steinernema carpocapsae Weiser, 1955 TUR-S4 isolate, and Steinernema feltiae Weiser, 1955 (Rhabditida: Steinernematidae) TUR-S3 and S-Bilecik isolates. These species were applied to Tenebrio molitor L., 1758 (Coleoptera: Tenebrionidae) larvae at 5, 10, and 15 Infective Juveniles (IJs) doses, under 1, 4, 7, 10, and 13% soil moisture conditions. The study was conducted in 2024 at Bursa Uludağ University, Faculty of Agriculture, Department of Plant Protection, Nematology Laboratory. As a result, the highest mortality rates on T. molitor larvae were obtained at 13% soil moisture with 15 IJs, 100% for HBH, 93.33% for TUR-S4, 86.67% for TUR-S3, and 83.33% for S-Bilecik. This study carries important implications for understanding the relationship between EPN efficacy on hosts and soil moisture.

Heterorhabditis alii n. sp. (Nematoda: Heterorhabditidae), a novel entomopathogenic nematode from Egypt used against the fall armyworm, Spodoptera frugiperda (Smith 1797) (Lepidoptera: Noctuidae)

BackgroundIsolation of novel species of entomopathogenic nematodes (EPNs) with biocontrol potential against important insect pests is very important for the sustainable management of economic pests damaging food crops and providing protection to the agricultural environment. This study was aimed to new indigenous EPN isolates from Egyptian agricultural soils and studies its biocontrol potential for further use in the biological control programs. Five out of 15 soil samples obtained from a farm located at the Cairo–Alexandria desert highway was positive for the presence of EPN, using the greater wax moth baiting method.ResultsSequencing of the internal transcribed spacer (ITS) region of 4 of the nematode isolates suggested that they belong to the species Heterorhabditis indica. However, one isolate does not show a high similarity to any of the H. indica previously recorded in the database of the Gen Bank and hence was identified as a new Heterorhabditis species and was deposited at the National Center for Biotechnology Information (NCBI) and registered under accession no. (OP555450) under the name of Heterorhabditis alii. This new species was also registered in the ZooBank under the registration link of: LSID urn: lsid: zoobank.org: act: 306F9D57-CC30-4B8E-8B19-4F0E42B08F34. No males were found in this species. Morphological characterization using the light microscope (LM) and scanning electron microscope (SEM) confirmed the identification of this nematode as a new species of the genus Heterorhabditis. Moreover, virulence of this new species against the fall armyworm (FAW), Spodoptera frugiperda (Smith 1797) (Lepidoptera: Noctuidae) was tested in comparison with the foreign EPN species, Heterorhabditis bacteriophora (HP88) and the local Heterorhabditis indica (Mango 2 isolate) and proved to be more effective against this devastative insect pest than the two compared species.ConclusionsThe present study found out a new species of the EPN genus, Heterorhabditis in Egypt. Our results were confirmed by both morphological and molecular analyses. The efficacy of this new species against the FAW proved to be a potent and safe biocontrol agent that can be used in biological control programs against this invasive insect pest of corn in Egypt and other global countries.

Efficacy of different entomopathogenic nematode isolates, against the peach fruit fly, Bactrocera zonata (Saund.) (Diptera: Tephritidae)

BackgroundThe invasive peach fruit fly (PFF), Bactrocera zonata (Saunders) (Diptera: Tephritidae), is a native of Southeast Asia. Entomopathogens like nematodes, bacteria, viruses and fungi have been shown to be effective as a biological control agent against B. zonata. Evaluation the efficacy of different entomopathogenic nematode isolates (EPNs) belonged to the two families (Steinernematidae and Heterorhabditidae); (Steinernema carpocapsae (AII), S. carpocapsae (EGAZ10), Heterorhabditis bacteriophora (HP88) and H. indica (EGAZ2) was carried out against the full-grown larvae of B. zonata under laboratory, semi-field and field conditions.ResultsData revealed that in all the tested nematode isolates succeeded to reduce the emerging of the PFF, B. zonata compared to controls with significant differences. The LC50 values were 794.3, 1063.2, 1249.8 and 1446.8 IJs/ml, for S. carpocapsae (AII), S. carpocapsae (EGAZ10), H. bacteriophora (HP88) and H. indica (EGAZ2), respectively, at 3 days post treatments. The strain, S. carpocapsae (AII) was effective than S. carpocapsae (EGAZ10). Also, the strain H. bacteriophora (HP88) was more effective than H. indica (EGAZ2). Therefore, the combination between the effective two steinernematid strains (S. carpocapsae (AII) & S. carpocapsae (EGAZ10)) and the two heterorhabditis strains (H. bacteriophora (HP88) & H. indica (EGAZ2)) was efficient in the semi-field experiment. In field condition, the combination of the two efficient strains S. carpocapsae (AII) and H. bacteriophora (HP88) at the concentration of 3000 IJs/ml was more effective in controlling B. zonata causing mortality 97.5%. The Co-Toxicity factor values were − 67.6 for the combination of S. carpocapsae (AII) with S. carpocapsae (EGAZ10) which recorded an antagonistic effect. Also, antagonistic effects were observed for the combined application of H. bacteriophora (HP88) with H. indica (EGAZ2) (− 66.6) in semi-field application; and the same effect was recorded for the combination of S. carpocapsae (AII) with H. bacteriophora (HP88) (− 42.6) in field application.ConclusionAll EPNs’ experiments showed that the efficacy of foreign nematodes than the local ones. So, combination of the two highly effective imported strains gave satisfied results, especially in the field experiment.

Antifungal Effect of Metabolites from Bacterial Symbionts of Entomopathogenic Nematodes on Fusarium Head Blight of Wheat.

Fungal diseases such as Fusarium head blight (FHB) are significant biotic stressors, negatively affecting wheat production and quality. This study explored the antifungal activity of the metabolites produced by the bacterial symbionts of entomopathogenic nematodes (EPNs) against FHB-causing Fusarium sp. Fusarium graminearum. To achieve this, the symbiotic bacteria of nine EPN isolates from the EPN collection at the Agricultural Research Council-Small Grains (ARC-SG) were isolated from the cadavers of Galleria mellonella (Lepidoptera: Pyralidae) larvae after infection with EPNs. Broth cultures (crude) and their supernatants (filtered and autoclaved) of each bacterial isolate were used as bacterial metabolite treatments to test their inhibitory effect on the mycelial growth and spore germination of F. graminearum. Mycelial growth inhibition rates varied among both bacterial isolates and treatments. Crude metabolite treatments proved to be more effective than filtered and autoclaved metabolite treatments, with an overall inhibition rate of 75.25% compared to 23.93% and 13.32%, respectively. From the crude metabolite treatments, the Xenorhabdus khoisanae SGI 197 bacterial isolate from Steinernema beitlechemi SGI 197 had the highest mean inhibition rate of 96.25%, followed by Photorhabdus luminescens SGI 170 bacteria isolated from Heterorhabditis bacteriophora SGI 170 with a 95.79% mean inhibition rate. The filtered metabolite treatments of all bacterial isolates were tested for their inhibitory activity against Fusarium graminearum spore germination. Mean spore germination inhibition rates from Xenorhabdus spp. bacterial isolates were higher (83.91 to 96.29%) than those from Photorhabdus spp. (6.05 to 14.74%). The results obtained from this study suggest that EPN symbiotic bacterial metabolites have potential use as biological control agents of FHB. Although field efficacy against FHB was not studied, the significant inhibition of mycelial growth and spore germination suggest that the application of these metabolites at the flowering stage may provide protection to plants against infection with or spread of F. graminearum. These metabolites have the potential to be employed as part of integrated pest management (IPM) to inhibit/delay conidia germination until the anthesis (flowering stage) of wheat seedlings has passed.

First report and biological characteristics of Heterorhabditis amazonensis in the state of Paraná, Brazil.

Entomopathogenic nematodes (EPNs) from Heterorhabditidae and Steinernematidae families are extensively used to control insect pests. In Brazil, however, relatively few studies have identified and characterized these entomopathogens. The objective of this study was to identify and characterize an EPN isolate obtained from soil samples collected in the state of Paraná, Brazil. An isolate (UEL 08) of Heterorhabditis was detected in a soil sample collected from a pasture area cultivated with Brachiaria grass in Londrina, state of Paraná, Brazil (23°34'311''S, 050°58'298''W), using the insect-baiting technique with Galleria mellonella larvae as hosts. The nematode was identified through morphometric studies and molecular analyses based on amplification of the rDNA ITS region. Although we identified certain morphometric differences compared with the original description, the molecular data indicated that the ITS sequence obtained for the UEL 08 isolate is identical to the reference sequence of H. amazonensis (DQ665222) and presented 100% similarity. Thus, the findings of our morphological and molecular studies confirmed that the isolated nematode is H. amazonensis, which is the first time this species has been registered in Paraná. Study of the biological characteristics of H. amazonensis (UEL 08) revealed that the isolate has two distinct life cycles - one short (216 h) and the other long (288 h) - and produces two generations in both cycles. We observed that H. amazonensis (UEL 8) was pathogenic and virulent to the three evaluated hosts, although with different virulence against these hosts. The larvae of G. mellonella and Alphitobius diaperinus were more susceptible than adult Dichelops (Diacereus) melacanthus, with 100%, 85%, and 46% mortality, respectively. Furthermore, an in vivo production assay revealed a mean daily yield of 3.4 × 103 infective juveniles/g host larvae.

Indication and identification of entomopathogenic nematodes Rhabditida: Steinernematidae, Heterorhabditidae (a review)

Goal. Of the study is to analyze the peculiarities of the use of methods aimed at detecting and identifying beneficial microorganisms for plant protection — entomopathogenic nematodes (Rhabditida: Steinernematidae and Heterorhabditidae).
 Results. A review of methods commonly used in faunistic studies of entomopathogenic nematodes (Steinernematidae, Heterorhabditidae) is given here, discussing their advantages and limitation. A single standard for many of the methods discussed in this review does not currently exist, so different approaches are described whose effectiveness has been confirmed experimentally and is considered satisfactory. First of all, the methods of soil sampling and insect hosts sampling and techniques for isolation of entomopathogenic nematodes from different types of samples are described. The most important systematic features of entomopathogenic nematodes, approaches to their identification and the main methods required for routine species identification, primarily the production of micro specimens and their examination by light microscopy, are discussed below. Methods of electron microscopy, cross-breeding and molecular genetic studies of entomopathogenic nematodes are also described.
 Conclusions. The obtained data are of significant theoretical and practical importance, as they allow for an informed choice of the most optimal method of detecting and identifying entomopathogenic nematodes — potential bioagents against insect pests.

Susceptibility of adult Phlyctinus (Coleoptera: Curculionidae) to entomopathogens: A first look at potential differences in a newly revised species complex

AbstractPhlyctinus callosus and P. xerophilus (Coleoptera: Curculionidae) are two cryptic species of native entimine weevils, previously grouped together under the P. callosus sensu lato concept, that are pests of economic importance to the deciduous fruit and vine industry in the Western Cape province of South Africa. Laboratory bioassays were conducted using entomopathogenic fungi (EPF) isolates of Beauveria and entomopathogenic nematodes (EPNs), Heterorhabditis indica and Steinernema yirgalemense, to determine differences in susceptibility of adult P. callosus and P. xerophilus to potential biological control agents. The test arena used was 24‐well bioassay plates with an inoculation rate of 200 infective juveniles (IJs)/insect for EPNs and 5 × 105 conidia/insect for EPF. Insects were inoculated using a 12.7 mm filter paper impregnated with 50 μL of entomopathogen suspension. Infection was determined after 96 h incubation for EPNs through dissection of cadavers. Insects inoculated with EPF were incubated in the wells for 18 days and mortality recorded daily. Cadavers were surface sterilized and observed for overt mycosis. Differential susceptibility between P. callosus and P. xerophilus was observed in EPF but not in EPN bioassays. Differential susceptibility to EPF could be due to methodology. Low adult weevil pathogenicity was found for all entomopathogens, with variable results obtained from different bioassay batches.

Steinernema yirgalemense inoculum size and timing impact on the population dynamics of in vitro liquid culture shake flask production

Summary Optimising the in vitro liquid mass production process for entomopathogenic nematodes (EPN) is a critical step in the development of a cost-effective EPN biopesticide product. Recording the nematode population and growth dynamics in an Erlenmeyer shake flask environment is essential to gaining a better understanding of which factors may influence the final yield. Although infective juvenile (IJ) inoculum concentration has previously been studied, no consensus yet exists as to whether it influences the final yield. This study sought to determine the impact of IJ inoculum concentration and timing on the recovery, growth and yield of the South African EPN isolate of Steinernema yirgalemense in shake flasks. The results indicated that the IJ inoculum concentration positively affects the final IJ yield of 2.88 × 155 IJ ml−1. Moreover, at higher IJ inoculum concentrations, a higher number of reproductive females and males are produced, when recovery percentages were similar. The lowest IJ inoculum concentration treatment was also the only treatment to show signs of an unwanted second generation in the final yield. The IJ inoculation timing trials confirmed that once the bacterium, Xenorhabdus indica, has ended the exponential growth phase and entered the stationary phase, it is ideal to then inoculate the IJ. However, it was found that the S. yirgalemense can be inoculated into the X. indica bacteria solution after 36 h of growth, instead of after 44-48 h. These trials demonstrated the need for further optimisation to produce consistent yields of the highly pathogenic South African EPN isolate of S. yirgalemense.

Phenotypic and biochemical characterisation and pathogenicity assessment on Galleria mellonella L. (Lepidoptera: Pyralidae) of symbionts of the entomopathogenic nematode Heterorhabditis amazonensis Andalo et al., 2006

Phenotypic and biochemical characterisation and pathogenicity assessment on Galleria mellonella L. (Lepidoptera: Pyralidae) of symbionts of the entomopathogenic nematode Heterorhabditis amazonensis Andalo et al., 2006

Pathogenicity and Virulence of Different Concentrations of Brazilian Isolates of Entomopathogenic Nematodes Against Drosophila suzukii.

The invasive pest Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) was recently recorded in Brazil and constitutes a threat to fruit growing, mainly for small, soft fruits. Recent advances in research on ways of controlling D. suzukii involve the use of entomopathogenic nematodes (EPNs). In this context, the objective of this study was to evaluate the pathogenicity and virulence of four isolates in different concentrations against D. suzukii pupae. The EPN isolates used in trials were Steinernema brazilense IBCBn 06, S. carpocapsae IBCBn 02, Heterorhabditis bacteriophora HB, and H. amazonensis IBCBn 24. Both H. amazonensis IBCBn 24 and H. bacteriophora HB were effective in controlling D. suzukii as they caused a mortality rate of 86.25% and 80.0%, and virulence of 549.75 IJs/pupae and 787.75 IJs/pupae in the concentrations of 1800 IJs/ml and 5400 IJs/ml, respectively. The lowest lethal concentrations (LC50) of juveniles were found in host pupae with 771.63 IJs/ml of H. bacteriophora HB and 1115.49 IJs/ml of H. amazonensis IBCBn 24. Results showed that both EPNs, H. amazonensis IBCBn 24 and H. bacteriophora HB, could be promising eco-friendly biological agents to control D. suzukii.

Virulence of Native Isolates of Entomopathogenic Nematodes for the Management of White Grubs

An alternative to chemical control, entomopathogenic nematodes are very effective against insect pests. Native isolates of Steinernema siamkayai, S. carpocapsae, Heterorhabditis indica, H. bacteriophora, Heterorhabditis sp. and Oscheius sp. have been evaluated for their virulence against white grubs. Under laboratory conditions, S. glaseri was more susceptible to A. communis in potato. S. glaseri@ 2.5 x10 9 IJ/ ha showed the highest grub mortality of 83.33% and 19.04% tuber damage. The same dosage of Heterorhabditis sp. in pot culture caused 18.66% tuber damage and 74.05% larval mortality. Steirnernema glaseriand Heterorhabditis sp. effectiveness against the coleopteran insect pests of Anomala communis<?i> in potato was conducted under field conditions. The maximum grub mortality with S. glaseri at 2.5 x10 9 IJ/ ha was 71.33%. With Heterorhabditis sp. at 2.5 x10 9 IJ/ ha, the yield increased by 14.14 t/ ha while tuber damage was 24.99%. However, the nematode S. glaseri and Heterorhabditis sp. has its best ability to live at the lowest temperature in the field trial, Anomala communiswas successfully managed by S. glaseri followed Heterorhabditis sp. in potato. The natural distribution of the native isolates of EPNs may be used for local insect pest management.

Isolation and identification of entomopathogenic nematodes : Biological potential against Lepidopteran and Coleopteran pests

Isolation and identification of entomopathogenic nematodes : Biological potential against Lepidopteran and Coleopteran pests

Combined effect of entomopathogenic nematode, Heterorhabditis indica with entomopathogenic fungi, Metarhizium pinghaense and M. robertsii against the obscure mealybug, Pseudococcus viburni

In this study, we evaluated the combined application of entomopathogenic nematodes (EPN), Heterorhabditis indica, with entomopathogenic fungi (EPF), Metarhizium pinghaense or M. robertsii, against Pseudococcus viburni (Signoret), in laboratory trials. Three EPF-EPN combinations were used, where P. viburni was either exposed to the EPF and EPN isolates simultaneously or sequentially, at different time intervals. The combined application of H. indica with each of the two EPF isolates resulted in higher mortality of P. viburni, under laboratory conditions, relative to when applied individually. With sequential application, the H. indica and M. robertsii combination was shown to be more effective, resulting in 85 ± 3.1% and 88.8 ± 3.9% mortality after four and three days, respectively. Heterorhabditis indica combined with M. pinghaense was more effective for simultaneous application of the entomopathogens, resulting in 95 ± 6.5% mortality after five days. Insect mortality was mostly due to EPN infection. The single application of H. indica against P. viburni resulted in 76.3 ± 2.9% after 48 h, while M. pinghaense and M. robertsii resulted in 73.8 ± 7.9% and 82.5 ± 3.3% respectively, after a week. Interactions between H. indica and the two EPF isolates were shown to have an additive effect, when used simultaneously and sequentially. The results from the study indicate that the combined application of EPF and EPN could potentially be used as an alternative strategy for management of P. viburni in fruit production areas.

Efficacy of three local isolates of entomopathogenic nematodes against the tomato leafminer, Tuta absoluta (Meyrick)

The tomato leafminer, Tuta absoluta (Meyrick) a key pest of tomato both in greenhouses and open-fields, has spread rapidly throughout Iran. The efficiency of native isolates of three species of entomopathogenic nematodes (Steinernema feltiae, S. carpocapsae, Heterorhabditis bacteriophora) was evaluated against the tomato leafminer, T. absoluta larvae (outside leaf and inside galleries), and pupae at various concentrations and times in laboratory conditions. Experiments were conducted at 25 ± 2ºC, 65 ± 5% RH, and 16L:8D h photoperiod. S. feltiae nematode caused the highest mortality for larvae outside the gallery (53.61%), followed by 45% mortality for larvae inside galleries, and lowest mortality for pupae (3.88%). The effect of infective juveniles (IJ) and exposure time (ET) on larval mortality in different treatments showed a significant (P< 0.01) relationship between IJ and ET and their interactions. Mortality of the T. absoluta larvae and pupae rose with more IJ and longer exposure time. The LC50 for, S. feltiae, S. carpocapsae and H. bacteriophora were 156.01, 225.13, and 317.66 IJs/ml for the second instar larvae of T. absoluta (outside the gallery), 296.31, 305.23 and 320.66 IJs/ml for inside gallery, respectively. Therefore, S. feltiae was a more effective species and can be suggested for complementary studies for finding a suitable biocontrol agent of the pest.

Characterization of Steinernema feltiae (Rhabditida: Steinernematidae) Isolates in Terms of Efficacy against Cereal Ground Beetle Zabrus tenebrioides (Coleoptera: Carabidae): Morphometry and Principal Component Analysis.

One of the most dangerous pests of cereals is Zabrus tenebrioides and, in Poland, it is becoming a serious pest. Entomopathogenic nematodes (EPNs) seem to be a very promising, biological control agent for this pest. Native EPN populations are well adapted to local environmental conditions. The current study characterized three Polish isolates of the EPN Steinernema feltiae, which differed in their effectiveness against Z. tenebrioides. In the field, isolate iso1Lon reduced the pest population by 37%, compared with 30% by isolate iso1Dan and 0% by the iso1Obl isolate; the number of plants damaged by Z. tenebrioides in the presence of the different isolates reflected the results in terms of the decrease in pest population size. After incubation in the soil for 60 days, recovered EPN juveniles of all three isolates were able to infect 93-100% of the test insects, with isolate iso1Obl again showing the lowest effectiveness. The juveniles of isolate iso1Obl were also morphometrically distinct from the other two isolates, as revealed by principal component analysis (PCA), which helped to distinguish the EPN isolates. These findings showed the value of using locally adapted isolates of EPNs; two of the three isolates randomly selected from Polish soil outperformed a commercial population of S. feltiae.

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.

Biocontrol potential of endosymbiotic bacteria of entomopathogenic nematodes against the tomato leaf miner, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae)

BackgroundThe tomato leaf miner, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is a major pest of tomato plants threatening global tomato production. The control of the pest is becoming increasingly difficult due to the rapid development of resistance to insecticides. Entomopathogenic nematodes (EPNs) of families Steinernematidae and Heterorhabditidae are successful biocontrol agents for many insect pests. Recently, their bacteria, Xenorhabdus spp. and Photorhabdus spp. have attracted great attention due to their major role in the pathogenicity of EPNs. In the present study, the pathogenicity of eleven EPNs isolates belonging to Steinernema feltiae and Heterorhabditis bacteriophora species was screened against the 1st/2nd and 3rd/4th instar larvae of T. absoluta. The cell-free supernatants and cell suspensions of the symbiotic bacteria from the most efficient isolates were further evaluated for their biocontrol potential in the oral and contact treatments on the larvae of T. absoluta.ResultsKBC-4 and MCB-8 isolates of S. feltiae showed superior virulence relative to other EPNs species/isolates and induced 90% larval mortality against the 3rd/4th instar of T. absoluta larvae, whereas there were no clear differences in the efficacy of EPNs species/isolates against the 1st/2nd instar of T. absoluta. The 1st/2nd instar of T. absoluta larvae was more susceptible to cell-free supernatants and cell suspension of selected EPNs. The highest mortality (80%) was obtained from X. bovienii MCB-8 strain in the contact treatment of supernatants. In contact treatment of cell suspension, higher mortalities were obtained compared to oral treatments. Mortality rates ranged between 30 and 57.5% in the contact treatments of cell suspensions while the highest mortality did not exceed 20% in oral treatments. The antifeedant activity was observed in oral treatments of cell suspension and most of the larvae avoided feeding on treated leaves.ConclusionThe results indicated that symbiotic bacteria of EPNs had a great potential against T. absoluta larvae and contact treatment of cell-free supernatants against early instars of T. absoluta can be an ideal application. However, further studies are needed to investigate the field effectiveness of symbiotic bacteria.

Virulence and reproductive potential of Indian entomopathogenic nematodes against the larvae of the rice meal moth

Entomopathogenic nematodes (EPNs) are key biocontrol agents against various insect pests such as pests of stored foods, when other control measures, such as pesticides are not appropriate. We evaluated the virulence and reproductive potential of four EPN isolates: Heterorhabditis bacteriophora MK263023, H. bacteriophora MK256358, H. bacteriophora MK256378 and S. cholashanense MH128155 against the larvae of the rice meal moth. These isolates were highly effective against the 4th instar larvae of the insect. All the isolates killed 100% of the insects within 24–48 h using 200 infective juveniles (IJs)/larvae. Similar mortality rates were observed at lower nematode concentrations, but more time was required. Heterorhabditis bacteriophora MK256358 and S. cholashanense MH128155 showed the best performance in killing and reproductive potential. Our results open new avenues for the potential of indigenous EPNs to effectively control this insect and set the basis for establishing safe strategy in its management programs in India.