In Vitro Chemotactic Responses of Three Gastropod-Associated Nematode Species to Selected Maize-Derived Volatile Organic Compounds

Plant-derived volatile organic compounds (VOCs) play a key role in belowground chemical communication and are known to influence the host-searching behaviour of entomopathogenic nematodes (EPNs). However, little is known about whether gastropod-associated nematodes perceive and respond to these rhizosphere chemical cues. The objective of this study was to investigate the in vitro chemotactic responses of the slug-parasitic nematode Phasmarhabditis papillosa and the facultatively parasitic nematodes Oscheius myriophilus and Oscheius onirici to three maize-derived terpenoids (α-humulene, linalool, and β-caryophyllene). Chemotaxis assays were conducted on agar under controlled laboratory conditions at three temperatures (15, 20, and 25 °C) and three VOC concentrations (pure compound, 1 ppm, and 0.03 ppm). Each treatment consisted of ten biological replicates and the experiment was repeated three times. Nematode motility and chemotaxis index (CI) were evaluated after 24 h, and the data were analysed using multifactor analysis of variance (ANOVA). Nematode motility and chemotactic behaviour were significantly influenced by nematode species, VOC identity, concentration, temperature, and several interaction effects (p < 0.05). Among the tested compounds, linalool consistently elicited the strongest positive chemotactic responses, particularly in O. myriophilus (maximum CI = 0.25), whereas α-humulene generally induced neutral or weakly repellent responses and β-caryophyllene produced variable, species-dependent effects. Overall, O. myriophilus exhibited the highest sensitivity to maize-derived VOCs, while O. onirici showed the weakest behavioural responses. These findings demonstrate that gastropod-associated nematodes exhibit species-specific behavioural responses to maize-derived VOCs under controlled laboratory conditions and contribute to a better understanding of their chemical ecology. Future studies should evaluate these responses in natural soils and with more complex blends of plant-derived volatiles to determine their ecological relevance and potential significance under field conditions.