Intercropping Reduces Root Pest Damage via Repellent Volatile Compounds: Insights From Behavioural Assays and Transcriptomic Analysis

Terrestrial plants naturally produce chemical signals to attract beneficial insects or repel harmful pests. These inherent plant attributes offer promising opportunities for eco-friendly pest control in agriculture, particularly through the push-pull intercropping technique. However, our understanding of potential repellent plants and their effective chemical signals remains limited. In this study, we evaluated multiple plant species for their repellent properties, identified effective volatile organic compounds, and investigated the mechanisms for controlling the fungus gnat Bradysia odoriphaga in Chinese chives. Among the 12 species tested, Mentha haplocalyx, Ocimum basilicum and Pelargonium graveolens demonstrated strong repellent effects, making them promising candidates as 'push' plants. Eight major volatile compounds were identified as effective repellents, with 1,8-cineole being the most efficient. 1,8-cineole consistently exhibited repellent effects against the fungus gnats across various concentrations and exposure durations. Transcriptomic analysis revealed that exposure to 1,8-cineole upregulated genes is associated with energy production processes, suggesting that the fungus gnats can detect and actively avoid this compound. Field experiments further confirmed the effectiveness of this strategy, as intercropping chives with M. haplocalyx significantly reduced fungus gnat infestations. This study presents a novel intercropping approach for managing fungus gnats and offers valuable insights into sustainable eco-friendly pest management practices in agriculture.