Abstract: An endophytic actinomycete strain Fq24 was isolated from healthy tomato plants. The acaricidal substances in the metabolites from Fq24 were collected and identified by the methods of extraction, column chromatography, and gas chromatography-mass spectrometry (GC-MS), and their bioactivities against Tetranychus cinnabarinus were measured with slide-dip and leaf-residue methods. Among the extracts, petroleum ether extract had high bioactivity in contact toxicity and oviposition deterrent against T. cinnabarinus. Its lethal concentration of 50% (LC₅₀) was 52.57 mg·L^-1, and its oviposition deterrent concentration of 50% (ODC₅₀) was 43.18 mg·L^-1. The identification with GC-MS showed that the main chemical component of fraction S₁₁ was methyl hexadecanoate, whose molecular formula was C₁₇H₃₄O₂, being one of the substances with acaricidal activity in the metabolites from Fq24.The24 h corrected mortality rate of female mite at 5 mg·mL^-1 of methyl hexadecanoate was 78.3%, and the oviposition deterrent rate was 81.6%.

Key words: methyl hexadecanoate, endophytic actinomycete Fq24, Tetranychus cinnabarinus, bioactivity