Acaricidal activity of components of Cryptomeria japonica against spider mites

The acaricidal activities of solvent extracts and essential oil obtained from Cryptomeria japonica were investigated. The two target spider mites (Tetranychus kanzawai and T. urticae), are known pests for various crops. The C. japonica leaves, barks, and heartwood were extracted by hexane, ethyl acetate and methanol successively, and acaricidal activities were tested by the leaf disc method. Acaricidal activity was observed on a hexane extract of C. japonica leaves. Next, the acaricidal activities of essential oil obtained from leaves by hot water distillation was tested and found to show stronger effects than the hexane extract. Elemol and ent-kaurene were found as the active components of essential oil. The LC₅₀values of ent-kaurene were quite lower than those of elemol and essential oil. Acaricidal activities of essential oil were mainly caused by ent-kaurene. Since other chemotypes of C. japonica are known in major diterpene hydrocarbon, we examined the acaricidal activity of phyllocladene and ent-sclarene. The activity of ent-sclarene was lower than ent-kaurene, and phyllocladene was much lower than ent-sclarene. Thus, the extract of C. japonica leaves containing ent-kaurene could be used as an interim pesticide when commercial pesticides are being changed or as a matrix of commercial pesticide.