Isolation, identification, and insecticidal activity of chromone compounds from Trichoderma harzianum against Aedes aegypti larvae

Five chromone derivatives were isolated and characterized from the fermentation products of Trichoderma harzianum ABC19819, including 5-hydroxy-2,3-dimethyl-7-methoxychromone (1), 5-hydroxy-3-acetoxymethyl-2-methyl-7-methoxychromone (2), 5-hydroxy-3-acetoxymethyl-2-methyl-7-methoxychromone (3), 5-hydroxy-2-hydroxymethyl-3-methyl-7-methoxychromone (4), and 5-hydroxy-2,3-dihydroxymethyl-7-methoxychromone (5), among which compound 5 is a previously undescribed chromone derivative. Bioassay results indicated that compound 2 exhibited significant larvicidal activity against third-instar Aedes aegypti larvae, with median lethal concentration (LC₅₀) values of 230.74 μg/mL at 24 h and 191.56 μg/mL at 36 h post-treatment. The time-dependent enhancement of insecticidal efficacy suggests a time-dependent toxicodynamic mode of action, though the precise mechanism requires further investigation.