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

Previous studies have demonstrated that <i>Trichoderma</i> metabolites triggered aggregation behavior in <i>Coptotermes formosanus</i> (Blattodea: Rhinotermitidae). Building on this, the present work systematically evaluated the behavioral effects of three specific <i>Trichoderma</i> metabolites-phenol, ethyl 2,4-dioxovalerate, and diglycolic acid-and their synergistic interactions with insecticides. We hypothesized that these metabolites attract <i>C. formosanus</i> 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 <i>Trichoderma</i> metabolites as safe and effective behavioral regulators for <i>C. formosanus</i>. By enhancing insecticidal efficacy through attractant-toxicity synergy, they represent promising candidates for developing novel termite control strategies.