Population fluctuation of natural enemies including Amblyseius womersleyi, A eharai, Agistemus fleschneri, and predacious thrips showed the highest peak in mid-June but disappeared in July and August. However, the density of A. fleschneri increased after late Soptember in non-spray fields. In conventional spray fields, the density of Tetranychus kanzawai was lower than that in non-spray fields due to several pesticides applications. The density of natural enemies was very low as compared with that of non-spray fields. Despite several applications of pesticides, the population of T. kanzawai was not suppressed efficiently but increased continuously. The susceptibility of 20 pesticides commercially used for control of tea pests were evaluated to A. womersleyi at the recommended concentrations. Mancozeb, a fungicide, killed 100% of A. womersleyi and other fungicides also showed high toxicities. Most insecticides were highly harmful to A. womersleyi. Among the tested acaricides, fenbutatin oxide could be used for the T. kanzawai in view of IPM because it was less toxic to A. womersleyi than to T. kanzawai.
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