The agar plate dilution method was used to separate the microorganism reported in this paper. A sample soil of 0.5 kg obtained from Harbin city, China, was taken in a sterilized test tube and sterilized water was added thereto. After 10 min of setting, supernatant was obtained. The supernatant thus obtained was 100-fold diluted using sterilized water, and 0.1 ml of the diluted solution was distributed onto a yeast–malt extract (yeast extract 4 g l−1, malt extract 10 g l−1, glucose 4 g l−1, agar 20 g l−1 and distilled water 1 l, pH 7.0–7.2) taken in a petri dish and cultured at 28 °C for 15 days. Colonies formed on the yeast–malt extract agar, from which a single colony was isolated using a sterilized needle. The obtained colony was transferred to a fresh yeast–malt extract agar at regular intervals for 10 days, followed by submerged fermentation. Metabolites were extracted by adding 4 ml methanol to 2 ml whole broth and mixing intermittently for 3 h. The extracts were examined on two-spotted spider mites to determine whether they have acaricidal activity. Then, the metabolites with acaricidal activity were purified and their structures were determined.

To identify the isolated strain with acaricidal activity in the metabolites, morphological properties of cells, cultural characteristics of cells, morphological characteristics of colonies, physiological characteristics, utilization of a carbon source and 16S rDNA (Accession No: DQ768097 in National Center for Biological Information, Bethesda, MD, USA) were investigated. The strain was named S. avermitilis NEAU1069. It has been deposited at the China General Microbiology Culture Collection Center, Beijing, China (Accession No: CGMCC 2943).

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