Susceptibility to 20 insecticides in Scirtothrips dorsalis HOOD female adults collected from 17 tea fields in the south region of Kyoto Prefecture determined by leaf-dipping method during 1998-2000.
Acetamiprid, imidacloprid, nitenpyram (choloronicotinil), DMTP, acephate (organic phosphorus), chlorfenapyr (pyrrole) and emamectin benzoate (macrolide) were highly effective against more than 90% of the collected populations.
Methomyl (carbamate), bifenthrin (pyrethroid) and prothiofos (organic phosphorus) were highly effective against 70-90% of the collected populations.
Cartap (nereistoxin), acrinathrin, ethofenprox, halfenprox, fenpropathrin, fluvalinate and permethrin (pyrethroid) were highly effective against 40-65% of the collected populations.
Diafenthiuron and pyridaben were highly effective against only 20% of the collected populations.
There were no significant correlations between the susceptibility of the collected populations and the years after the registration of the insecticides.
The annual number of chemical spraying on tea fields in the collected sites varied from 5 to 19, and more than a half number of applications are registered against Scirtothrips dorsalis HOOD.

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The effects of chemicals on the population of the predatory mite Amblyseius womersleyi and its prey Tetranychus kanz-awai were evaluated when the tops or the inside of tea bushes were sprayed. The population densities of both species were counted from April to November in 1997, and chemicals were sprayed six times during the experiment. The densities of both species in the plot where the tops of the bushes were sprayed were the same as those in the untreated plot. The density of T. kanzawai in the plots where the tops and the inside of the bushes were sprayed was significantly higher than that in the untreated plot. Chemicals sprayed on the plucking surface did not significantly affect the predatory mite population, but spraying inside the leaf layer had significant effects. However, A. womersleyi controlled the population of T. kanzawai quite well even in the plot with inside spraying. Since the leaf layer of the tea bushes effectively blocked the penetration of chemicals, the.bush below the plucking surface is very important as a refuge for natural enemies.

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Re-sprouting of winter buds was observed in young tea fields (cultivar. Kuritawase) in southern Kyushu in the warm autumn-winter of 1984. Because this phenomenon could decrease yield and quality of the first crop in the next year, the regrowth of winter buds and several treatments for improvement were urgently studied. All combinations of times (no re-skiffing, late December and late February re-skiffing) and intensity (at the level of autumn skiffing and 2cm below the level of autumn skiffing) of re-skiffing after the regrowth were examined to determine influences on the first crop. Re-skiffing at the level of the autmn skiffing in late December just after the re-sprouting buds ceased growing effectively reduced deterioration in yield and quality of the first crop.

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