Search Results (12)

Root-emitted volatile organic compounds (VOCs) play a critical role in below-ground ecological interactions by mediating communication between plants, pests, and their natural enemies. This study investigates the chemotactic behavior of three slug-parasitic nematode species—Phasmarhabditis papillosa, Oscheius myriophilus, and Oscheius onirici—in response to four carrot (Daucus carota) root-derived VOCs: α-pinene, terpinolene, bornyl acetate, and 2-ethyl-1-hexanol. Using a modified Petri dish assay, infective juveniles (IJs) were exposed to each compound across four concentrations (pure, 1000 ppm, 10 ppm, and 0.03 ppm), and their directional movement was quantified using a chemotaxis index (CI). The results revealed strong species-specific and concentration-dependent patterns. O. myriophilus exhibited the highest motility and repellency, particularly toward bornyl acetate and terpinolene, indicating its potential for use in VOC-guided biocontrol strategies. O. onirici showed moderate but consistent attraction to most VOCs, while P. papillosa exhibited generally weak or repellent responses, especially at higher concentrations. None of the compounds tested functioned as strong attractants (CI ≥ 0.2), suggesting that plant-derived VOCs alone may not be sufficient to direct nematode recruitment under field conditions. However, their integration with other biotic cues could enhance nematode-based “lure-and-infect” systems for sustainable slug control in carrot cropping systems. Full article

The increasing environmental and health concerns associated with synthetic pesticides underscore the need for sustainable alternatives in pest management. This study investigates the chemotactic responses of five nematode species—Heterorhabditis bacteriophora, Steinernema carpocapsae, Steinernema feltiae, Phasmarhabditis papillosa, and Oscheius myriophilus—to three major cannabinoids from Cannabis sativa: Δ⁹-tetrahydrocannabinol (THC), cannabigerol (CBG), and cannabidiol (CBD). Using a standardized chemotaxis assay, we quantified infective juvenile movement and calculated Chemotaxis Index (CI) values across varying cannabinoid concentrations. Our results revealed strong species-specific and dose-dependent responses. THC and CBG elicited significant attractant effects in P. papillosa, S. feltiae, and H. bacteriophora, with CI values ≥ 0.2, indicating their potential as behavioral modulators. In contrast, CBD had weaker or repellent effects, particularly at higher concentrations. O. myriophilus exhibited no consistent response, underscoring species-specific variation in chemosensory sensitivity. These findings demonstrate the potential utility of cannabinoids, especially THC and CBG, as biocompatible cues to enhance the efficacy of nematode-based biological control agents in integrated pest management (IPM). Further field-based studies are recommended to validate these results under realistic agricultural conditions. Full article

Parasitic nematodes play a vital role in soil ecosystems, contributing to natural pest suppression. Among them, slug-parasitic species such as Phasmarhabditis papillosa (Schneider) Andrassy, Oscheius myriophilus (Poinar), and Oscheius onirici Torrini et al. are promising biological control agents against mollusk pests. These nematodes rely on plant-emitted volatile organic compounds (VOCs) for host location, yet their chemotactic responses to specific VOCs remain unclear. This study assessed the responses of P. papillosa, O. myriophilus, and O. onirici to VOCs emitted by potato (S. tuberosum) tubers under varying temperature (18 °C, 22 °C) and concentration conditions (pure compound, 0.03 ppm). The results indicate that octanal was the strongest attractant, particularly for O. myriophilus, while nonanal exhibited species-dependent effects. Hydrocarbons such as undecane and 1,2,4-trimethylbenzene had minimal or repellent effects, whereas 6-methyl-5-hepten-2-one showed moderate attraction. Chemotactic responses were stronger at 18 °C, and attraction increased with higher VOC concentrations, suggesting a threshold-dependent response. These findings enhance our understanding of plant–nematode interactions and suggest that octanal and 6-methyl-5-hepten-2-one could improve nematode-based slug control strategies. However, environmental factors such as soil composition and microbial activity may influence VOC diffusion and nematode recruitment. Future research should focus on optimizing VOC formulations, assessing field applicability, and integrating these findings into sustainable pest management programs. Full article

Parasitic nematodes, particularly those in the Rhabditidae family, are vital components of belowground ecosystems, contributing to pest regulation and sustainable agriculture. This study investigated the chemotactic responses of three nematode species—Phasmarhabditis papillosa, Oscheius myriophilus, and O. onirici—to volatile organic compounds (VOCs) emitted by Brassica nigra roots under herbivory by Delia radicum larvae. Using a chemotaxis assay, the effects of five VOCs (dimethyl sulfide, dimethyl disulfide, allyl isothiocyanate, phenylethyl isothiocyanate, and benzonitrile) were tested at two concentrations (pure and 0.03 ppm) and two temperatures (18 °C and 22 °C). The results revealed that VOCs and temperature significantly influenced nematode responses, while nematode species and VOC concentration showed limited effects. Benzonitrile consistently demonstrated strong chemoattractant properties, particularly for O. myriophilus and O. onirici. Conversely, allyl isothiocyanate exhibited potent nematicidal effects, inhibiting motility and causing mortality. Dimethyl disulfide and dimethyl sulfide elicited moderate to strong attractant responses, with species- and temperature-dependent variations. Significant interactions between VOCs, temperature, and nematode species highlighted the complexity of these ecological interactions. These findings emphasize the ecological roles of VOCs in mediating nematode behavior and their potential applications in sustainable pest management. Benzonitrile emerged as a promising candidate for nematode-based biocontrol strategies, while allyl isothiocyanate showed potential as a direct nematicidal agent. The study underscores the importance of integrating chemical cues into pest management systems to enhance agricultural sustainability and reduce reliance on chemical pesticides. Full article

The grey garden slug (Deroceras reticulatum), a common terrestrial slug native to Europe with a global distribution including North America, is commonly considered the most severe slug pest in agriculture. The nematode Phasmarhabditis hermaphrodita, which has been used in the U.K. and Europe as a commercial biocontrol agent since 1994, has also recently been collected in Oregon and California and has long been considered a candidate biocontrol agent for slug management in the U.S. In this study, we report differential gene expressions in nematode-infected slugs using RNA-seq to identify slug immune-related genes against nematodes. Comparison of gene expression levels between the whole bodies of a nematode-infected slug (N-S) and an uninfected control slug (C-S) revealed that there were a total of 39,380 regulated unigenes, of which 3084 (3%) were upregulated and 6761 (6%) were downregulated at greater than 2-fold change (FC > 2) in the nematode-infected slug. To further investigate the biological functions of differentially expressed genes (DEGs), gene ontology (GO) and functional enrichment analysis were performed to map the DEGs to terms in the GO, eukaryotic ortholog groups of proteins (KOG) and Kyoto Encyclopedia of Genes and Genome Pathway (KEGG) databases. Among these DEGs, approximately 228 genes associated with immunity or immune-related pathways were upregulated 2-fold or more in the N-S compared to C-S. These genes include toll, Imd, JNK, scavenger receptors (SCRs), C-type lectins (CTLs), immunoglobulin-like domains, and JAK/STAT63 signaling pathways. From the RNA-seq results, we selected 18 genes and confirmed their expression levels by qRT-PCR. Our findings provide insights into the immune response of slugs during nematode infection. These studies provide fundamental information that will be valuable for the development of new methods of pest slug control using pathogenic nematodes in the field. Full article

The effect of wireworm-damaged lettuce roots on the antioxidative defense system (ascorbate–glutathione cycle, photosynthetic pigments) and movement of insect/slug parasitic nematodes towards determined root exudates was studied in a glasshouse experiment. Lettuce seedlings were grown in a substrate soil in the absence/presence of wireworms (Elateridae). The ascorbate–glutathione system and photosynthetic pigments were analyzed by HPLC, while volatile organic compounds (VOC) emitted by lettuce roots were investigated by GC-MS. Herbivore-induced root compounds, namely 2,4-nonadienal, glutathione, and ascorbic acid, were selected for a chemotaxis assay with nematodes Steinernema feltiae, S. carpocapsae, Heterorhabditis bacteriophora, Phasmarhabditis papillosa, and Oscheius myriophilus. Root pests had a negative effect on the content of photosynthetic pigments in the leaves of infested plants, indicating that they reacted to the presence of reactive oxygen species (ROS). Using lettuce as a model plant, we recognized the ascorbate–glutathione system as a redox hub in defense response against wireworms and analyzed its role in root-exudate-mediated chemotaxis of nematodes. Infected plants also demonstrated increased levels of volatile 2,4-nonadienal. Entomopathogenic nematodes (EPNs, S. feltiae, S. carpocapsae, and H. bacteriophora) proved to be more mobile than parasitic nematodes O. myriophilus and P. papillosa towards chemotaxis compounds. Among them, 2,4-nonadienal repelled all tested nematodes. Most exudates that are involved in belowground tritrophic interactions remain unknown, but an increasing effort is being made in this field of research. Understanding more of these complex interactions would not only allow a better understanding of the rhizosphere but could also offer ecologically sound alternatives in the pest management of agricultural systems. Full article

Between July and September 2021, researchers collected 100 specimens of the Spanish slug, Arion vulgaris, and dissected their cadavers to examine them for parasitic nematodes. Molecular techniques were used to identify the nematodes, which confirmed the presence of Oscheius myriophilus, marking the first recorded instance of this nematode in a gastropod host. To test the virulence of Slovenian strains of O. myriophilus and Phasmarhabditis papillosa and their effects on the feeding behavior of the Spanish slug, grey field slug (Deroceras reticulatum), and vineyard snail (Cernuella virgata), laboratory bioassays were conducted using nematodes grown in vivo. Nematodes were applied at various doses ranging from 10 to 500 nematodes/gastropod. The results showed that O. myriophilus and P. papillosa caused significant mortality (82.5% ± 2.5% at 15 °C) of the Spanish slug while being less effective against the vineyard snail and grey field slug. Nematodes were more virulent at a lower temperature (15 °C) than at the higher temperature (20 °C) tested in the experiment. Additionally, both nematode species significantly reduced gastropod herbivory. The potential use of O. myriophilus and P. papillosa as biological control agents against gastropods is discussed. Full article

Succinea snails are considered to be invasive and pestiferous gastropods to those in the floricultural industry. Their small size makes them difficult to locate within large plant shipments, and their presence on decorative plants can constitute for an entire shipment to be rejected for sale and distribution. Research performed on Succinea snails is limited, especially in terms of effective mitigation strategies. The nematode Phasmarhabditis hermaphrodita is a biological control agent used on pestiferous gastropods throughout some European nations. Here, three strains of Phasmarhabditis from the United States (P. hermaphrodita, P. californica, and P. papillosa) were assessed as biological control agents against Succinea snails in controlled laboratory conditions, along with the molluscicide Sluggo Plus^® as a control. All species of Phasmarhabditis applied at 30 IJs/cm² caused significant mortality compared to the non-treated control and treatment with Sluggo Plus^®. P. californica caused 100% mortality 6 days after exposure, while P. hermaphrodita and P. papillosa caused the same mortality rate 7 days after exposure. The molluscicide was unable to cause significant mortality compared to the non-treated control. Additional research with US Phasmarhabditis strains, including their non-target effects and distribution may lead to their being a viable option for biological control against Succinea snails. Full article

The grey field slug, Deroceras reticulatum, is an agricultural pest causing damage to a wide variety of crops each year. The nematode Phasmarhabditis hermaphrodita has been shown to effectively kill this slug in field-simulated conditions, leading to its widespread use as a biological control agent in Europe. However, recently discovered isolates of Phasmarhabditis from California have not been tested in a field-simulated environment. The lethality of three local isolates of Phasmarhabditis (P. hermaphrodita, P. californica, & P. papillosa) as well as the molluscicide Sluggo Plus^® was assessed on D. reticulatum in a lath house. Remaining leaf area on Canna lilies and slug mortality were recorded after 3 weeks of exposure to treatments. Local isolates efficiently killed D. reticulatum and protection from leaf damage was attained by treatment with P. papillosa. Further experimentation is required to assess plant protection afforded by Phasmarhabditis as plants in some trials may have been in poor health. The three tested Phasmarhabditis isolates are reasonable candidates for biological control within the United States but additional information, particularly on the lethality to non-target gastropods, is needed before an informed decision on their use can be made. Full article

Classic biological control of pest non-marine molluscs has a long history of disastrous outcomes, and despite claims to the contrary, few advances have been made to ensure that contemporary biocontrol efforts targeting molluscs are safe and effective. For more than half a century, malacologists have warned of the dangers in applying practices developed in the field of insect biological control, where biocontrol agents are often highly host-specific, to the use of generalist predators and parasites against non-marine mollusc pests. Unfortunately, many of the lessons that should have been learned from these failed biocontrol programs have not been rigorously applied to contemporary efforts. Here, we briefly review the failures of past non-marine mollusc biocontrol efforts in the Pacific islands and their adverse environmental impacts that continue to reverberate across ecosystems. We highlight the fact that none of these past programs has ever been demonstrated to be effective against targeted species, and at least two (the snails Euglandina spp. and the flatworm Platydemus manokwari) are implicated in the extinction of hundreds of snail species endemic to Pacific islands. We also highlight other recent efforts, including the proposed use of sarcophagid flies and nematodes in the genus Phasmarhabditis, that clearly illustrate the false claims that past bad practices are not being repeated. We are not making the claim that biocontrol programs can never be safe and effective. Instead, we hope that in highlighting the need for robust controls, clear and measurable definitions of success, and a broader understanding of ecosystem level interactions within a rigorous scientific framework are all necessary before claims of success can be made by biocontrol advocates. Without such amendments to contemporary biocontrol programs, it will be impossible to avoid repeating the failures of non-marine mollusc biocontrol programs to date. Full article

The spreading of alien and invasive species poses new challenges for the ecosystem services, the sustainable production of food, and human well-being. Unveiling and targeting the immune system of invasive species can prove helpful for basic and applied research. Here, we present evidence that a nematode (Phasmarhabditis hermaphrodita)-based molluscicide exerts dose-dependent lethal effects on the golden apple snail, Pomacea canaliculata. When used at 1.7 g/L, this biopesticide kills about 30% of snails within one week and promotes a change in the expression of Pc-bpi, an orthologue of mammalian bactericidal/permeability increasing protein (BPI). Changes in Pc-bpi expression, as monitored by quantitative PCR (qPCR), occurred in two immune-related organs, namely the anterior kidney and the gills, after exposure at 18 and 25 °C, respectively. Histological analyses revealed the presence of the nematode in the snail anterior kidney and the gills at both 18 and 25 °C. The mantle and the central nervous system had a stable Pc-bpi expression and seemed not affected by the nematodes. Fluorescence in situ hybridization (FISH) experiments demonstrated the expression of Pc-bpi in circulating hemocytes, nurturing the possibility that increased Pc-bpi expression in the anterior kidney and gills may be due to the hemocytes patrolling the organs. While suggesting that P. hermaphrodita-based biopesticides enable the sustainable control of P. canaliculata spread, our experiments also unveiled an organ-specific and temperature-dependent response in the snails exposed to the nematodes. Overall, our data indicate that, after exposure to a pathogen, the snail P. canaliculata can mount a complex, multi-organ innate immune response. Full article

Lethal effects of neem derived pesticides (neem leaf extract (NLE) and NeemAzal-T/S (NA)) were examined on different entomopathogenic (EPN) and slug-parasitic (SPN) nematodes. In our recent study, neem derived pesticides were tested against Phasmarhabditis hermaphrodita for the first time under in vitro conditions. Laboratory experiments were set up in 96-well microplates with different concentrations of NLE (0.1%, 0.3%, 0.6%, and 1%) and NA (0.001%, 0.003%, 0.006%, and 0.01%) and Milli-Q water as the control. After 24-h exposure time, mortality of individual nematodes was observed and recorded. Considering LC₁₀ values, 0.1% of NLE could be used safely in combination with all the EPNs and SPNs tested in recent study. A concentration of NA three times higher than the recommended dosage did not harm either EPN or SPN species. In conclusion, NeemAzal-T/S might be applied with EPNs and the SPN Ph. hermaphrodita simultaneously, while the compatibility of neem leaf extract and beneficial nematode products needs further evaluation. Full article