Dual Role of Tenebrio molitor Frass in Sustainable Agriculture: Effects on Free-Living Nematodes and Suppression of Meloidogyne incognita.

Insect-derived frass is gaining attention as a circular bioeconomy product with fertilizing and pest-suppressive potential. This study investigates Tenebrio molitor frass as a soil amendment for promoting beneficial nematodes and suppressing Meloidogyne incognita. A 40-day pot experiment on clay loam soil tested with six inputs: raw and heat-treated frass (0.5%, 1% w/w), Melia azedarach fruit powder (1.6%), and an untreated control. Soil nematode communities were assessed at 5 and 40 days after application (DAA), and nematicidal activity was evaluated in vitro. Raw frass at 1% induced a rapid response from free-living nematodes at 5 DAA, with increased abundance of bacterivorous taxa such as Rhabditis and Acrobeloides, alongside a higher Enrichment Index (EI), indicating short-term nutrient availability. At 40 DAA, only 1% raw frass consistently supported more cp-1 bacterivores and slightly increased Shannon diversity. Network analysis revealed more connected, modular structures in raw frass treatments, suggesting enhanced food web complexity. However, omnivore and predator effects were limited. Raw frass extracts caused over 80% paralysis of Meloidogyne incognita juveniles within 24 h, significantly outperforming heat-treated frass and Melia extracts. T. molitor frass moderately stimulates opportunistic nematodes and provides strong nematicidal effects, supporting its potential as a multifunctional input for sustainable soil management.