Infectivity Of Entomopathogenic Nematodes Research Articles

The Activin Branch Ligand Daw Regulates the Drosophila melanogaster Immune Response and Lipid Metabolism against the Heterorhabditis bacteriophora Serine Carboxypeptidase.

Despite impressive advances in the broad field of innate immunity, our understanding of the molecules and signaling pathways that control the host immune response to nematode infection remains incomplete. We have shown recently that Transforming Growth Factor-β (TGF-β) signaling in the fruit fly Drosophila melanogaster is activated by nematode infection and certain TGF-β superfamily members regulate the D. melanogaster anti-nematode immune response. Here, we investigate the effect of an entomopathogenic nematode infection factor on host TGF-β pathway regulation and immune function. We find that Heterorhabditis bacteriophora serine carboxypeptidase activates the Activin branch in D. melanogaster adults and the immune deficiency pathway in Activin-deficient flies, it affects hemocyte numbers and survival in flies deficient for Activin signaling, and causes increased intestinal steatosis in Activin-deficient flies. Thus, insights into the D. melanogaster signaling pathways and metabolic processes interacting with H. bacteriophora pathogenicity factors will be applicable to entomopathogenic nematode infection of important agricultural insect pests and vectors of disease.

Effect of male parental gamma irradiation on host suitability of its F1 progeny of a lepidopteran tropical pest, Spodoptera litura (Fabr.) towards development and virulence of entomopathogenic nematodes, Steinernema thermophilum

The suitability of F1 progeny insect larvae of the irradiated male parent, Spodoptera litura (Fabr.) for infective juveniles (IJs) of entomopathogenic nematodes (EPN), Steinernema thermophilum was assessed to comprehend the feasibility of combining EPNs with nuclear pest control tactic. As compared to the control, the IJs induced faster host mortality with reduced proliferation in F1 host larvae. IJs derived from F1 host larvae exhibited almost similar proliferation capacity on normal hosts as in control. Further, the molecular basis of EPNs induced mortality in F1 host larvae was evaluated. Dual stress of EPN infection and irradiation induced downregulation of the relative mRNA expression of antimicrobial genes and upregulated expression of antioxidative genes. A pronounced effect of EPNs in association with irradiation stress was apparent on host mortality. Radiation induced sterile F1 insect larvae of S. litura acted as a reasonably suitable host for EPNs and also provided the environment for developing viable EPNs for their potential use as biocontrol agents.

A laboratory study on survival and infectivity of entomopathogenic nematodes formulated in gum katira-based biogel compositions

A laboratory study on survival and infectivity of entomopathogenic nematodes formulated in gum katira-based biogel compositions

The Efficacy of Entomopathogenic Nematodes Plus an Adjuvant against Helicoverpa zea and Chrysodeixis includens in Aboveground Applications.

In the southern United States, corn earworm, Helicoverpa zea (Boddie), and soybean looper, Chrysodeixis includens (Walker) are economically important crop pests. Although Bt crops initially provided effective control of target pests such as H. zea, many insect pests have developed resistance to these Bt crops. Alternative approaches are needed, including biological control agents such as entomopathogenic nematodes (EPNs). However, the effectiveness of EPNs for aboveground applications can be limited due to issues such as desiccation and ultraviolet radiation. Effective adjuvants are needed to overcome these problems. Ten strains of EPNs were tested for virulence against eggs, first to fourth instars, fifth instars, and pupae of H. zea and C. includens in the laboratory. These 10 EPN strains were Heterorhabditis bacteriophora (HP88 and VS strains), H. floridensis (K22 strain), Hgkesha (Kesha strain), Steinernema carpocapsae (All and Cxrd strains), S. feltiae (SN strain), S. rarum (17c+e strain), and S. riobrave (355 and 7-12 strains). EPNs could infect eggs of H. zea or C. includens in the laboratory, but the infection was low. The mortality caused by 10 EPN strains in seven days was significantly higher for the first to fourth instars of H. zea compared to the control, as was the fifth instars of H. zea. Similarly, for the first to fourth and fifth instars of C. includens, the mortality was significantly higher compared to the controls, respectively. However, only S. riobrave (355) had significantly higher mortality than the control for the pupae of H. zea. For the pupae of C. includens, except for H. bacteriophora (HP88), S. rarum (17c+e), and H. floridensis (K22), the mortality of the other seven strains was significantly higher than the control. Subsequently, S. carpocapsae (All) and S. riobrave (7-12) were chosen for efficacy testing in the field with an adjuvant 0.066% Southern Ag Surfactant (SAg Surfactant). In field experiments, the SAg Surfactant treatment significantly increased the mortality and EPN infection for S. carpocapsae (All) on first instars of H. zea in corn plant whorls. On soybean plants, with the SAg Surfactant, S. carpocapsae (All) was more effective than S. riobrave (7-12) on fifth instars of C. includens. This study indicates that EPNs can control H. zea and C. includens, and SAg Surfactant can enhance EPN efficacy.

Compatibility of Entomopathogenic Nematodes with Chemical Insecticides for the Control of Drosophila suzukii (Diptera: Drosophilidae).

The spotted-wing drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), is a pest that reduces the productivity of small fruits. Entomopathogenic nematodes (EPNs) and chemical insecticides can suppress this pest, but the compatibility of the two approaches together requires further examination. This laboratory study evaluated the compatibility of Steinernema brazilense IBCBn 06, S. carpocapsae IBCBn 02, Heterorhabditis amazonensis IBCBn 24, and H. bacteriophora HB with ten chemical insecticides registered for managing D. suzukii pupae. In the first study, most insecticides at the recommended rate did not reduce the viability (% of living infective juveniles (IJs)) of S. braziliense and both Heterorhabditis species. The viability of S. carpocapsae was lowered by exposure to spinetoram, malathion, abamectin, azadirachtin, deltamethrin, lambda-cyhalothrin, malathion, and spinetoram after 48 h. During infectivity bioassays, phosmet was compatible with all the EPNs, causing minimal changes in infectivity (% pupal mortality) and efficiency relative to EPN-only controls, whereas lambda-cyhalothrin generally reduced infectivity of EPNs on D. suzukii pupae the most, with a 53, 75, 57, and 13% reduction in infectivity efficiency among H. bacteriophora, H. amazonensis, S. carpocapsae, and S. brazilense, respectively. The second study compared pupal mortality caused by the two most compatible nematode species and five insecticides in various combinations. Both Heterorhabditis species caused 78-79% mortality among D. suzukii pupae when used alone, and were tested in combination with spinetoram, malathion, azadirachtin, phosmet, or novaluron at a one-quarter rate. Notably, H. bacteriophora caused 79% mortality on D. suzukii pupae when used alone, and 89% mortality when combined with spinetoram, showing an additive effect. Novaluron drastically reduced the number of progeny IJs when combined with H. amazonensis by 270 IJs and H. bacteriophora by 218. Any adult flies that emerged from EPN-insecticide-treated pupae had a shorter lifespan than from untreated pupae. The combined use of Heterorhabditis and compatible chemical insecticides was promising, except for novaluron.

Exploring entomopathogenic nematodes for the management of Lobesia botrana (Lepidoptera: Tortricidae) in vineyards: Fine-tuning of application, target area, and timing

Lobesia botrana (Lepidoptera: Tortricidae) is a crucial grapevine pest worldwide. Expanding the available biocontrol agents can provide new management strategies compatible with organic viticulture. Entomopathogenic nematode (EPN) potential as a biocontrol agent was demonstrated against various developmental stages of L. botrana. For its field application, we hypothesised that by selecting the best combination of EPN-adjuvant and identifying the best area/timing for their application, we will secure their effective implementation against L. botrana. The aim of this study was to determine the best ecological scenarios for their use against L. botrana. We investigate three EPN species naturally occurring in Riojan vineyards: Steinernema feltiae, S. carpocapsae, and Heterorhabditis bacteriophora. We evaluated (i) EPN viability, infectivity, and adherence on leaves combined with adjuvants (Multi-Us, Maximix, Dash HC, Nu-Film-17, and Adrex), (ii) EPN biocontrol against L. botrana larva on leaves and grapes and damage reduction, and (iii) EPN efficacy against L. botrana at 22°, 15°, and 10 °C. Overall, all the adjuvants were compatible with the EPN, except Adrex with Heterorhabditis bacteriophora. Compared with the no application, EPNs (steinernematids) alone or with Maximix increased L.botrana L3 mortality on grapes and leaves, thereby reducing the damage. Pupal mortality caused by steinernematids EPN (alone or with Maximix) decreased with temperature, from ∼60% at 22 °C to <30% at 10 °C. Overall, steinernematids EPN (alone or with Maximix) applied against L. botrana on leaves, grapes, or trunks reduced the damage and increased insect mortality. This study suggests the best-case scenario for the application of EPNs is at sunset during late spring/early autumn at mid-temperatures (22 °C-15 °C). Further field validation is necessary for their full implementation.

Increasing the survival and efficacy of entomopathogenic nematodes on exposed surfaces by Pickering emulsion formulations offers new venue for foliar pest management

Formulation technology has been the primordial focus to improve the low viability and erratic infectivity of entomopathogenic nematodes (EPNs) for foliar application. Adaptability to the fluctuating environment is a key trait in ensuring the survival and efficacy of EPNs. Hence, tailoring formulations towards EPNs foliar applications would effectively deliver consistent and reliable results for above-ground applications. EPNs survival and activity were characterized in novel Pickering emulsion post-application in planta cotton foliage. Two different types of novel formulations, Titanium Pickering emulsion (TPE) and Silica Pickering emulsion Gel (SPEG), were tailored for EPNs foliar applications. We report an extension of survival and infectivity to 96 hrs under controlled conditions by SPEG formulations for survival of IJ's on cotton foliage. In addition, survival of IJs (LT50) was extended from 14hrs in water to > 80 hrs and > 40 hrs by SPEG and TPE respectively. SPEG accounted for the slowest decrease of live IJs per surface area in comparison to TPE and control samples over time, exhibiting a 6-fold increase at 48 hrs. Under extreme conditions, survival and efficacy were extended for 8hrs in SPEG compared to merely 2hrs in control. Potential implications and possible mechanisms of protection are discussed.

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.

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.

Metabonomics reveals that entomopathogenic nematodes mediate tryptophan metabolites that kill host insects.

The entomopathogenic nematode (EPN) Steinernema feltiae, which carries the symbiotic bacterium Xenorhabdus bovienii in its gut, is an important biocontrol agent. This EPN could produce a suite of complex metabolites and toxin proteins and lead to the death of host insects within 24-48 h. However, few studies have been performed on the key biomarkers released by EPNs to kill host insects. The objective of this study was to examine what substances produced by EPNs cause the death of host insects. We found that all densities of nematode suspensions exhibited insecticidal activities after hemocoelic injection into Galleria mellonella larvae. EPN infection 9 h later led to immunosuppression by activating insect esterase activity, but eventually, the host insect darkened and died. Before insect immunity was activated, we applied a high-resolution mass spectrometry-based metabolomics approach to determine the hemolymph of the wax moth G. mellonella infected by EPNs. The results indicated that the tryptophan (Trp) pathway of G. mellonella was significantly activated, and the contents of kynurenine (Kyn) and 3-hydroxyanthranilic acid (3-HAA) were markedly increased. Additionally, 3-HAA was highly toxic to G. mellonella and resulted in corrected mortalities of 62.50%. Tryptophan metabolites produced by EPNs are a potential marker to kill insects, opening up a novel line of inquiry into exploring the infestation mechanism of EPNs.

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.

Deadly scents: Exposure to plant volatiles increases mortality of entomopathogenic nematodes during infection.

Plants attacked by insects commonly mobilize various defense mechanisms, including the biosynthesis and release of so-called herbivore-induced plant volatiles (HIPVs). Entomopathogenic nematodes (EPNs) can be attracted to these belowground HIPVs, which can enhance biocontrol services from EPNs. However, recent research has also demonstrated that HIPVs can induce and initiate insect immune responses, decreasing the insect’s susceptibility to pathogens and parasites. Therefore, experiments were conducted to test the impact of HIPVs on insects and EPNs during the initial stage of EPN infection. Compounds that can impact EPN attraction and infectivity such as pregeijerene, β-caryophyllene, and α-pinene, and compounds that have been determined to increase or decrease susceptibility of insects to pathogens, such as (Z)-3-hexenyl acetate, linalool, and β-ocimene, were selected. Exposure of Galleria mellonella larvae to pregeijerene, linalool, β-ocimene and α-pinene during invasion significantly increased mortality of Steinernema diaprepesi and Heterorhabditis bacteriophora after 48 h. Larval treatment with β-caryophyllene only increased mortality for Heterorhabditis bacteriophora. (Z)-3-hexenyl acetate did not cause differential mortality from the controls for either nematode species. In additional experiments, we found that EPNs exposed to α-pinene and linalool were more readily recognized by the insects’ immune cells compared to the control treatment, thus the observed increased mortality was likely due to HIPVs-EPN interactions with the insect’s immune system. These results show that the presence of HIPVs can impact EPN survival in the model host, G. mellonella.

Indigenous entomopathogenic nematode as biocontrol agents for insect pest management in hilly regions

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.

Infectivity of entomopathogenic nematode against the cabbage butterfly (Pieris brassicae L.) in polyhouse and in field condition

BackgroundCabbage butterfly, Pieris brassicae Linnaeus (Lepidoptera: Pieridae), is a major insect pest affecting cole crops worldwide. Excessive applications of chemical-based insecticides have a devastating impression over the organisms and environment.ResultsIn this study, entomopathogenic nematode (EPN) Heterorhabditis bacteriophora Poinar strain EUPT-S26 (local isolate) was evaluated for Pieris brassicae control under polyhouse and field conditions. Under the polyhouse conditions, the highest insect mortality 91.6 and 94.0% was observed in the plots treated with the nematodes suspension 1500 IJs/ml and 2000 IJs/ml, respectively. Based on the highest cabbage plant protection under polyhouse conditions, H. bacteriophora EUPT-S26 was also applied for field assays in the course of the crop’s productive phase. Data demonstrated from the field treatments signify the highest concentration (2000 IJs/ml) showed the maximum larval mortality and least damage percentage 45 ± 1.07% that remained constant until harvesting; this resulted in the highest productivity in polyhouse and under field conditions.ConclusionAccording to assessed field conditions, it was suggested to perform 3 applications of EPNs during the vegetative phase and at the time of head formation to increase productivity and to reduce damage. The results approved that EPNs are an effective alternative of chemical-based insecticides to control the cabbage butterfly.

Culturing and Genetically Manipulating Entomopathogenic Nematodes.

Entomopathogenic nematodes in the genera Heterorhabditis and Steinernema are obligate parasites of insects that live in the soil. The main characteristic of their life cycle is the mutualistic association with the bacteria Photorhabdus and Xenorhabdus, respectively. The nematode parasites are able to locate and enter suitable insect hosts, subvert the insect immune response, and multiply efficiently to produce the next generation that will actively hunt new insect prey to infect. Due to the properties of their life cycle, entomopathogenic nematodes are popular biological control agents, which are used in combination with insecticides to control destructive agricultural insect pests. Simultaneously, these parasitic nematodes represent a research tool to analyze nematode pathogenicity and host anti-nematode responses. This research is aided by the recent development of genetic techniques and transcriptomic approaches for understanding the role of nematode secreted molecules during infection. Here, a detailed protocol on maintaining entomopathogenic nematodes and using a gene knockdown procedure is provided. These methodologies further promote the functional characterization of entomopathogenic nematode infection factors.

Non-lethal effects of entomopathogenic nematode infection

Entomopathogenic nematodes are typically considered lethal parasites of insect hosts. Indeed they are employed as such for biological control of insect pests. The effects of exposure to entomopathogenic nematodes are not strictly limited to mortality, however. Here we explore non-lethal effects of exposure to entomopathogenic nematodes by introducing the relatively non-susceptible pupal stage of Delia antiqua to thirteen different strains. We specifically chose to inoculate the pupal stage because it tends to be more resistant to infection, yet resides in the soil where it could come into contact with EPN biological control agents. We find that there is no significant mortality at the pupal stage, but that there are a host of strain-dependent non-lethal effects during and after the transition to adulthood including altered developmental times and changes in risk of death compared to controls. We also find that exposure to specific strains can reduce risk of mortality. These results emphasize the strain-dependent nature of entomopathogenic nematode infection and highlight the positive and negative ramifications for non-lethal effects for biological control of insect pests. Our work emphasizes the need for strain-specific screening of biological control agents before wide-spread adoption.

Climate Change Modulates Multitrophic Interactions Between Maize, A Root Herbivore, and Its Enemies

How climate change will modify belowground tritrophic interactions is poorly understood, despite their importance for agricultural productivity. Here, we manipulated the three major abiotic factors associated with climate change (atmospheric CO2, temperature, and soil moisture) and investigated their individual and joint effects on the interaction between maize, the banded cucumber beetle (Diabrotica balteata), and the entomopathogenic nematode (EPN) Heterorhabditis bacteriophora. Changes in individual abiotic parameters had a strong influence on plant biomass, leaf wilting, sugar concentrations, protein levels, and benzoxazinoid contents. Yet, when combined to simulate a predicted climate scenario (Representative Concentration Pathway 8.5, RCP 8.5), their effects mostly counter-balanced each other. Only the sharp negative impact of drought on leaf wilting was not fully compensated. In both current and predicted scenarios, root damage resulted in increased leaf wilting, reduced root biomass, and reconfigured the plant sugar metabolism. Single climatic variables modulated the herbivore performance and survival in an additive manner, although slight interactions were also observed. Increased temperature and CO2 levels both enhanced the performance of the insect, but elevated temperature also decreased its survival. Elevated temperatures and CO2 further directly impeded the EPN infectivity potential, while lower moisture levels improved it through plant- and/or herbivore-mediated changes. In the RCP 8.5 scenario, temperature and CO2 showed interactive effects on EPN infectivity, which was overall decreased by 40%. We conclude that root pest problems may worsen with climate change due to increased herbivore performance and reduced top-down control by biological control agents.

Potential of in vivo- and in vitro-cultured entomopathogenic nematodes to infect Lobesia vanillana (Lepidoptera: Tortricidae) under laboratory conditions.

Entomopathogenic nematodes (EPNs) have been successfully applied as biological control agents against above ground and soil stages of insect pests. However, for commercial application, it is crucial to mass culture these nematodes using in vitro liquid culture technology, as it is not attainable when using susceptible insects as hosts. Lobesia vanillana (Lepidoptera: Tortricidae) is regarded a sporadic pest of wine grapes in South Africa. The in vivo- and in vitro-cultured South African EPNs, Steinernema yirgalemense and Steinernema jeffreyense (Rhabditida: Steinernematidae), were evaluated against larvae and pupae of L. vanillana in laboratory bioassays. For larvae, high mortality was observed for all treatments: In vitro-cultured S. yirgalemense (98%) performed better than S. jeffreyense (73%), while within in vivo cultures, there was no difference between nematode species (both 83%). No significant difference was detected between in vivo- and in vitro cultures of the same nematode species. The LD50 of the in vitro-cultured S. yirgalemense, was 7.33 nematodes per larva. Mortality by infection was established by dissecting L. vanillana cadavers and confirming the presence of nematodes, which was > 90% for all treatments. Within in vitro cultures, both S. yirgalemense and S. jeffreyense were able to produce a new cohort of infective juveniles from L. vanillana larvae. Pupae, however, were found to be considerably less susceptible to EPN infection. This is the first study on the use of EPNs to control L. vanillana. The relative success of in vitro-cultured EPN species in laboratory assays, without any loss in pathogenicity, is encouraging for further research and development of this technology.

Chemical host-seeking cues of entomopathogenic nematodes.

Entomopathogenic nematodes (EPNs) are obligate parasites that infect a broad range of insect species. Host-seeking is a crucial step for EPN infection success and survival. Yet, the identity and ecological functions of chemicals involved in host-seeking by EPNs remain overlooked. In this review, we report known CO2, plant-derived and insect-derived cues shaping EPN host-seeking and recognition. Despite species-specific response to environmental cues, we highlight a hierarchical integration of chemicals by EPNs. We further emphasize the impact of EPN selection pressure, age, and experience on their responsiveness to infochemicals. Finally, we feature that EPN chemical ecology can translate into powerful sustainable strategies to control insect herbivores in agriculture.

Nanopore-Sequencing Characterization of the Gut Microbiota of Melolontha melolontha Larvae: Contribution to Protection against Entomopathogenic Nematodes?

This study focused on the potential relationships between midgut microbiota of the common cockchafer Melolontha melolontha larvae and their resistance to entomopathogenic nematodes (EPN) infection. We investigated the bacterial community associated with control and unsusceptible EPN-exposed insects through nanopore sequencing of the 16S rRNA gene. Firmicutes, Proteobacteria, Actinobacteria, and Bacteroidetes were the most abundant bacterial phyla within the complex and variable midgut microbiota of the wild M. melolontha larvae. The core microbiota was found to include 82 genera, which accounted for 3.4% of the total number of identified genera. The EPN-resistant larvae differed significantly from the control ones in the abundance of many genera belonging to the Actinomycetales, Rhizobiales, and Clostridiales orders. Additionally, the analysis of the microbiome networks revealed different sets of keystone midgut bacterial genera between these two groups of insects, indicating differences in the mutual interactions between bacteria. Finally, we detected Xenorhabdus and Photorhabdus as gut residents and various bacterial species exhibiting antagonistic activity against these entomopathogens. This study paves the way to further research aimed at unravelling the role of the host gut microbiota on the output of EPN infection, which may contribute to enhancement of the efficiency of nematodes used in eco-friendly pest management.