The Acaricidal Principal From External Seed Coat Of Ginkgo Biloba L.

The strong acaricidal activity of the extract by 90% ethyl alocohol from the Ginkgo biloba L. seeds against Panonychus citri (Mcg.) is reported here for the first time (LC₅₀=48.3mg/L, LC₉₀=94.1mg/L). Furthermore, its yield was 20.4%. While the extract by water showed no acaricidal activity (LC₅₀=5295mg/L, LC₉₀=29139mg/L). Among the soxhlet extractions of the extract by 90% ethyl alocohol, the strong acaricidal activity was only found to be in the non-polar fraction, petroleum ether (b. p. 60-90℃) extract, which percentage was 87.2%0. The petroleum ether (b. p. 60-90℃) extract was purified by means combined silica gel chromatography and Sephadex LH-20 molecular sieve, using LC₅₀ and LC₉₀ as toxicity factors. Finally, a compound (A) with high acaricidal activity (LC₅₀=5.3mg/L, LC₉₀=13.1mg/L) was obtained. HPLC showed that the purity of the compound was 94.3%.The acaricidal substance extracted from Ginkgo biloba external seed coat was identified by UV, IR, El-MS, ¹H-NMR and ¹³C-NMR as 6-[(Z)-10-heptadecenyl]-2-hydroxybenzoic acid (A). Laboratory bioassay on citrus red mite, Panonychus citri, showed that compound A possessed the following properties: (1) Powerful contact toxicity with an LC₅₀ of 5.3 mg litre^-1 after 24 h that was similar to pyridaben (LC₅₀= 3.3 mg litre^-1) and significantly superior to omethoate (LC₅₀=117 mg litre^-1). Furthermore, its LC₉₀ was 13.1 mg litre^-1 after 24 h that is significantly superior to both pyridaben (LC₉₀= 24.7 mg litre^-1) and omethoate (LC₉₀= 358 mg litre^-1). (2) Quick-acting acaricidal activity. At identical concentrations, compound A was much faster than pyridaben or omethoate. (3) Compound A had strong corrosive action to the cuticle of P citri but no phytotoxicity to plants.Based on the powerful contact and acute toxicity of the compound A, we try to use this compound for acaricide. Suitable emulgator can enhance the virulence of the compound of Ginkgo biloba L.. Field experiments showed that, the compound A is reasonable for acaricide.To see whether compound A was phytotoxic, the leaves, flowers and buds of plants including Citrus unshiu Marc., Citrus nobilis Lour., Pyrus hopeiensis Yu. and Malus pumila Mill. sprayed with solutions of compound A (in the concentration range from 25.0 to 10000 mg litre^-1) had been observed for three months. The treated plants didn't show any abnormality.