Attraction-Mediated Synergy: Insecticide Toxicity Against Coptotermes formosanus Enhanced by Trichoderma Metabolites

Previous studies have demonstrated that Trichoderma metabolites triggered aggregation behavior in Coptotermes formosanus (Blattodea: Rhinotermitidae). Building on this, the present work systematically evaluated the behavioral effects of three specific Trichoderma metabolites-phenol, ethyl 2,4-dioxovalerate, and diglycolic acid-and their synergistic interactions with insecticides. We hypothesized that these metabolites attract C. formosanus through multiple behavioral mechanisms and enhance the toxicity of insecticides. Bioactivity showed that ethyl 2,4-dioxovalerate and diglycolic acid exhibited no significant toxicity. Phenol (5 × 10^-2 to 5 µg/cm) and ethyl 2,4-dioxovalerate (5 × 10^-1 µg/cm) elicited trail-following behavior. In the no-choice insecticide synergy test, phenol or diglycolic acid combined with imidacloprid (50 µg/g) resulted in substantially higher mortality compared to insecticides alone. The combination of metabolites with fipronil resulted in 100% mortality in termites. In two-choice aggregation tests, termite presence on metabolite-treated filter papers was significantly elevated compared to the controls. Fipronil (10 μg/g) alone significantly reduced termite aggregation. But when fipronil was combined with the metabolites, termite presence on the treated papers increased significantly, resulting in a substantial rise in mortality and demonstrating a clear attract-kill synergy. These findings identify Trichoderma metabolites as safe and effective behavioral regulators for C. formosanus. By enhancing insecticidal efficacy through attractant-toxicity synergy, they represent promising candidates for developing novel termite control strategies.