Oriental persimmon, Diospyros kaki Thunb., endemic to East Asia is one of the major fruit crops in Korea. We conducted the faunal survey of mites on persimmon trees in Korea from June to September 2006, especially focusing on herbivorous and predacious mites. Mites of Tetranychidae and Tenuipalpidae were dominantly collected as herbivores, while those of Phytoseiidae and Stigmaeidae were predominant as predators. All identified tenuipalpid mites were Tenuipalpus zhizhilashviliae Reck. Most of the collected tetranychid mites were found to belong to the genus Tetranychus. To clarify the species identity, additional collections of tetraychid mites during summer 2007 on sweet persimmon were made. The mites were identified as Tetranychus urticae Koch. Four phytoseiid species, Neoseiulus womersleyi (Schicha), Amblyseius eharai Amitai and Swirski, Phytoseius (Dubininellus) rubii Xin, Liang and Ke and Typhlodromus (Anthoseius) vulgaris Ehara were collected. Among them, A. eharai was the most dominant species. Seventeen populations of two spotted mites (TSM) were observed 3 times per month from May to October to figure out their fluctuations at the site of individual farmer’s orchard from Sacheon, Sancheong, and Jinju in Gyeongsangnam- do and Gwangyang, Gurye, and Suncheon in Jeollanam-do. Among them, only 2 sites were properly managed, 5 sites were required to control but the farmers had little information on the mite and its damage, though 10 orchards were not in jeopardy. Number of TSM reached more than 400 at its maximum when 100 leaves were randomly observed at orchards from Sacheon, Okgok, and Muncheok, showing remarkably discolored leaves. For the control of TSM in fields by chemical means, it was tried to select an effective miticides in persimmon fields. Control activity of spiromesifen 20SC showed 99.0% and 98.1% and the activity of acequinocyl 15SC showed 90.8% and 99.0% in Jinju and Sacheon at 20 days after treatment, respectively. It was tried to understand the cause of the fluctuations of TSM populations on the viewpoints of pesticide spray, density of predacious mites, rainfalls, and weeds in the persimmon orchards. Various factors considered to contribute to the cause of population fluctuations, depending upon the situations of each orchard. To develop as a potential resource of biological control agents, it was tried to find out winter spatial distribution and movement of Amblyseius eharai (Acari: Phytoseiidae) on persimmon trees in Korea using artificial materials. We attached Phyto traps and urethane foam on persimmon trees in early November 2007 in Sacheon, Korea to estimate overwintering ecology of the predominant phytoseiid species Amblyseius eharai on persimmon. Most of A. eharai were found on the samples of branches, such as pedicel. In early spring, A. eharai was abundantly collected in the weekly and long-term traps before the leaf extension of persimmon trees, which additionally enhanced the possibility that A. eharai overwintered on the trees.

Neoseiulus californicus (McGregor) is a potential biological control agent of spider mites in orchards. The field occurrence of this species was first reported from citrus orchards in Jeju Island and recently this mite started to be sold as a commercial product in Korea. However, the natural occurrence of N. californicus in the Korean mainland is unclear or quite limited. At this time, it is not certain whether N. californicus can overwinter in the Korean mainland or not. This mite is presently planning to be used as a biological control agent against spider mites in apple orchards of the Korean mainland. The main objective of this study was to investigate natural overwintering sites of N. californicus and possible factor increasing winter survival of this species, to develop effective method for collecting overwintering population of N. californicus. For the first objective, we conducted field survey in two citrus orchards of Jeju in early and late February 2008. Samples were collected from various possible overwintering sites: citrus trees, ground covers and windbreaks. Total 259 phytoseiid mites were collected, 94% of the mites were identified as N. californicus and 98% of them were adult females. Most of N. californicus were collected from ground covers, specially the weed species which had rosette leaves: Youngia japonica (L.) DC. and Erigeron spp. This result seemed to suggest that N. californicus try to hide beneath weed leaves near ground surface during winter to get successful survival. Thus, the second experiments were conducted in Andong from December 2007 to early March 2008. N. californicus conditioned in a greenhouse with natural day length was individually put in a small tube, and the tubes were kept under different ground surface conditions: bare, fallen leaves and urethane foam. When water had been added in the tube, the mites on bare ground had died after one month, while 70% of the mites of the other cover treatments were surviving. In these cover treatments, 7-10% of the mites had survived until two months, and eventually all died within three months. This result showed that hiding under cover structure near ground surface may be effective to increase winter survival of N. californicus. Therefore, collecting weeds which have rosette leaves may be an effective method to estimate of the overwintering possibility of N. californicus in the Korean mainland.

As suggested by Kawashima (2006), the most abundant Tetranychidae was Tetranychus sp. as a pest in persimmon orchards. The observatory orchards were selected 16 in total, 2 from Gurye, 2 from Gwangyang, and 2 from Suncheon in Jeonnam Province and 3 from Jinju, 4 from Sacheon, and 3 from Sancheong in Gyeongnam Province. Number of mites in 100 persimmon leaves were observed from each orchards nearly every ten days. Careful rearing of the mites sample collected from the four observaory persimmon fields at which the mite had occurred the most seriously among 16 fields and results from taxanomical identification process indicated that the species was identified Tetranychus urticae. Maximum number of T. urticae reached to 436 on 27 June at Jeongdong, Sacheon, 108 on 1 August at Sinann, Sancheong, 406 on 26 June Okgok, Gwangyang, and 509 on 15 June Muncheok, Gurye. When the number reached to more than 400 mites, the persimmon leaves changed from clear yellow dots, to pale yellow, and to grey in the backside. An experiment was conducted to control T. urticae and to select highly active miticide in persimmon orchards in Jinju and Sacheon. Spiromesifen 20SC and acequinosyl 15 SC were effective.

Neoseiulus californicus (McGregor), which is a potential biological control agent of spider mites, has been produced by some Korean natural enemy companies. Now, our project related to the biological control of spider mites by releasing N. californicus in apple orchards is going on. The field occurrence of this species in Korea was first reported in Jeju citrus orchards (Jung et al. 2006). However, the natural occurrence of the mite has not been recorded in Korean mainland so far. Therefore, it is questioned whether the released N. californicus population originated in Jeju can successfully overwinter in Korean mainland. First, to clarify the natural overwintering sites in field, we conducted field samplings in Jeju citrus orchards in Feb. 2008. Samples were collected from the various possible overwintering habitats, such as citrus leaves and twigs, ground covers and windbreaks. Most of the mites were collected from ground cover samples. Next, to estimate of the winter mortality, the mite was individually put in small tubes which have some different food conditions, and the tubes were kept under the different ground surface conditions in the university experimental orchard in Dec. 2007. Most of the mites had died by late Jan. and all by early Mar. 2008. And also, to evaluate the field survival of the mite, in the spring 2008, sampling would be conducted in apple orchards in Cheongsong where we released the mites in 2007. From these data, we would discuss possible overwintering of N. californicus in Korea.