Slugs are significant agricultural pests, causing considerable economic damage. Their control predominantly relies on the use of chemical plant protection products. However, due to the adverse environmental impacts of pesticides, researchers are increasingly seeking environmentally friendly alternatives. One such solution is biocontrol, utilizing slug-parasitic nematodes as beneficial organisms. In Slovenia, the nematode Oscheius onirici was isolated from the Spanish slug in 2023. This species is relatively unknown globally, and its efficacy in biocontrol remains largely unexplored. Plants under herbivore attack can emit volatile organic compounds (VOCs) that attract natural enemies. While past studies have shown that VOCs can influence the movement of entomopathogenic nematodes, significantly less is known about their effects on slug-parasitic nematodes. In this study, we examined the response of O. onirici to a selection of VOCs: α-pinene, α-humulene, allyl isothiocyanate, benzonitrile, β-caryophyllene, bornyl acetate, camphor, decanal, dimethyl disulfide, phenylethyl isothiocyanate, linalool, nonanal, terpinolene, and undecane. The nematodes were tested at two temperatures (18°C and 20°C) and two concentrations (100% and 0.001%). The results showed that terpinolene, α-humulene, α-pinene and β-caryophyllene acted as weak repellents, while phenylethyl isothiocyanate and undecane demonstrated stronger repellent effects. Linalool emerged as a weak attractant, whereas the other compounds showed no significant influence on nematode movement. Importantly, VOCs were found to impact the mobility of infective nematode larvae, with the highest mobility observed in the presence of linalool and terpinolene. These findings highlight the potential role of VOCs in modulating nematode behavior and provide a foundation for further investigation into the biocontrol potential of O. onirici.
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