In 2005, the invasion of Bemisia tabaci Q-type was detected at first in the southern part of Korea. And then the pest has been spread rapidly over the nation, and it has attacked various fruit vegetables including yellow melon, tomato, sweet pepper, and so on. During three years since 2005, many kinds of predators and parasitoids have been applied to establish the biological control program to solve the Bemisia tabaci problem. Parasitoids were regarded as promising natural enemies, at first. However, Encarsia formosa famous for the parasitoid of greenhouse whitefly is not so effective to control Bemisia tabaci. Although other parasitoids, Eretmocerus eremicus and Eretmocerus mundus, were introduced successively, application results of them were not satisfactory. Owing to the difficulties in settling the parasitoids on crops, total cost of biological control program tends to be increased by the iterative periodic release. On the other hand, it was great that the application result of predatory mite, Amblyseius swirskii. Laboratory experiments show that the mite can consume large amount of Bemisia tabaci eggs. In addition, the mite can survive and reproduce without prey. Plant-associated materials such as pollens are sufficient for the development and reproduction of the mite. Field observations reveal that just onetime release after the first blossom is enough for the preventive treatment. The mite is especially so effective on the pollen-rich crops such as sweet pepper. Flowers and leaves are infested by the mite in a brief instant. While flower-dwelling mites take a role of natural enemy of thrips, leaf-dwelling mites effectively suppress the density of Bemisia tabaci. Anyway, curative treatment of the mite is not desirable, for it usually do not feed on other stage of Bemisia tabaci except fresh eggs within one or two days. It is also unfortunate that the mite seldom moves on tomato. It is even reluctant to go out from distribution box. When we put some mites on a leaf of tomato, they usually aggregated in a point. Sticky trichomes and semiochemicals might be engaged in such phenomena. In addition, the mite seems to be suffered by high temperature. So the density of Bemisia tabaci could be increased continuously in summer season, regardless of the presence of the predatory mite. In recent, we keep an eye on another predatory bug, Nesidiocoris tenuis, as a biological control agent against whiteflies on tomato. Nesidiocoris tenuis is an active and aggressive natural enemy. It likes to eat whitefly eggs, larvae and pupae. It can also feeds on aphids and mites. Once established in tomato greenhouse, whiteflies were overwhelmed by the predator. In our observation, Bemisia tabaci could be successfully controlled by the predator without any pesticide application, during about a half year from early spring to mid summer. However, we should take precaution against the side effects of Nesidiocoris tenuis, which is ironically known as a serious pest on tomato. From time to time, growing points of tomato could be disappeared by the damage of Nesidiocoris tenuis. So we need to control the density of the bug under the economic threshold. Owing to the bug, the production of sesame could be decreased remarkably. To avoid side effects, Nesidiocoris tenuis should be handled by the experts who know well about the ecological characteristics of it. In the case of yellow melon, biological control of any pest is not easy task. Without pesticide, yellow melon is frequently damaged destructively by aphids, mites and whiteflies. However, the temperature in greenhouse is too high to release and augment ordinary natural enemies. We just regard Nesidiocoris tenuis as a promising natural enemy of whiteflies on yellow melon, because it is resistant to high temperature. Many trials and errors might be required to establish reliable strategy to solve the problem caused by Bemisia tabaci. And it should be continued that the efforts for the integrated pest management based on biological control.

Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseidae) is well known as an effective natural enemy of two-spotted spider mite, Tetrnychus urticae Koch (Acari: Tetranychidae). However, successful biological control usually requires adequate management of temperature. While P. persimilis did suppress T. urticae at moderate condition (20~25oC) in a week or so, the density of P. persimilis was barely increased at cold condition (5~10oC) in three weeks or so. The problem is that winter temperature is too cold for the development and reproduction of P. persimilis in greenhouse for forcing strawberry. Night temperatures in greenhouse were even mostly lower than 6oC. So, winter application of P. persimilis against T. urticae is useless. To avoid damage from T. urticae in early spring season, it was better that the release amount of P. persimilis was double at middle- and late-October, instead of early-November to next early-February. If necessary, the double releasing of P. persimilis might be good for control of T. urticae at middle- and late-February.