Attraction of entomopathogenic nematodes to black truffle and its volatile organic compounds: A new approach for truffle beetle biocontrol

Abstract

The European truffle beetle, Leiodes cinnamomeus, is the most important pest in black truffle (Tuber melanosporum) plantations. Entomopathogenic nematodes (EPNs) are a promising biological control agents against L. cinnamomeus. EPNs may employ multiple sensory cues while seeking for hosts, such as volatile organic compounds (VOCs) and CO2 gradients. We report for the first time the attraction of EPNs to truffle fruitbodies, and identified some VOCs potentially playing a key role in this interaction. We conducted olfactometer assays to investigate the attraction behavior of Steinernema feltiae and Steinernema carpocapsae towards both T. melanosporum fruitbodies and larvae of L. cinnamomeus. Subsequently, a chemotaxis assay using agar plates was performed to determine which of the 14 of the main VOCs emitted by the fruitbodies attracted S. feltiae at low (0.1 %) and high (mg/100 g truffle) concentrations. Both EPN species were attracted to mature fruitbodies of T. melanosporum, which may enhance the likelihood of encountering L. cinnamomeus during field applications. L. cinnamomeus larvae in the presence of truffles did not significantly affect the behavior of EPNs 24 h after application, underscoring the importance of the chemical compounds emitted by truffles themselves. Chemotaxis assays showed that four long-chain alcohol compounds emitted by T. melanosporum fruitbodies attracted S. feltiae, especially at low concentration, providing a first hint in the chemical ecology of a little-studied ecological system of great economical value. Further studies should be conducted to gain a finer understanding of the tritrophic interactions between T. melanosporum, EPNs, and L. cinnamomeus, as this knowledge may have practical implications for the efficacy of EPNs in the biological control of this pest.