The two-spotted spider mite, Tetranychus urticae Koch is the most harmful pest among many cropping systems, particularly vegetables and other annual crops. In this study, the methanol extract from the inner bark of Tabebuia impetiginosa was evaluated for acaricidal activity against T. urticae by using a leaf disk method and were compared with commercial acaricide, abamectin. A crude methanol extract of T. impetiginosa had strongly acaricidal activity at 2,000 ppm against the T. urticae. Methanol extract of T. impetiginosa was partitioned with hexane, chloroform, ethyl acetate, butanol and water fraction, successively. In this result, the chloroform fraction showed a strong acaricidal activity at 1,000 ppm. Therefore, active fraction of T. impetiginosa extract was purified by using silica gel column chromatography and high performance liquid chromatography. The structure of acaricidal component was analyzed by EI-MS, 1H-NMR and 13C-NMR spectra, and was identified as TI-3123. Based on the LC50 values of TI-3123 and abamectin against T. urticae were resulted in 0.011 mg/l and 0.340 mg/l, respectively. These results showed that acaricidal activity of the T. impetiginosa can be mostly attributed to TI-3123. Furthermore, TI-3123 was approximately 30.91 times more toxic than abamectin against T. urticae. All these results suggested that active component in T. impetiginosa derived materials could be use for biological control for T. urticae. Further studies should be performed to the structure activity relationship of TI-3123 and compared with its derivatives.

Four major agricultural insect pests, Bemisia tabaci, Myzus persicae, Plutella xylostella and Tetranychus urticae, were irradiated with 30, 50, 70, or 100 Gy electron-beam. Longevity, egg hatching, emergence, and fecundity of the test insects were measured. Hatchability of B. tabaci, P. xylostella and T. urticae declined with increasing irradiation doses, and all B. tabaci and T. urticae eggs were dead at 100 Gy. When eggs of B. tabaci, P. xylostella and T. urticae were irradiated, hatch was inhibited. B. tabaci adults grown from 70 Gy irradiated eggs did not lay eggs. Fecundity of P. xylostella from the 100 Gy irradiated eggs decreased. When B. tabaci, P. xylostella, M. persicae and T. urticae nymphs/larvae were irradiated, the results were similar as those of the hatched eggs. When P. xylostella pupae were irradiated with 100 Gy, fecundity of emerged adults decreased and no eggs hatched. When B. tabaci, P. xylostella, M. persicae and T. urticae adults were irradiated with 70 and 100 Gy, fecundity decreased and egg hatch of B. tabaci was inhibited. However, the longevity of adults did not change and electron-beam irradiation of all developmental stages had no effect on the longevity of adults.

Twospotted spider mite, Tetranychus urticae was collected from the rose greenhouse in Gimhae, Gyeongnam province in Jan, 2001. Resistant strain was reared over nine years treated with Acequinocyl (over 400 times), and increased 614 folds as compared to susceptible strain (S). Cross resistance of acequinocylresistant strain adults to eight acaricide was showed high in Cyflumetofen (108 folds) and expressed low in Abamectin (16 folds), Tebufenpyrad (7.6 folds), Fenpyroximate (6.1 folds). Against Chlorfenapyr (0.5 folds), however, showed negatively correlated cross resistance. Synergistic effects with PBO (piperonyl butoxide), an oxygenase inhibitor, DEF (S,S,S-tributyl phosphorotrithioate), an esterase inhibitor, and DEM (diethymaleate), an inhibitor of glutathion S-transferase were also investigated. Synergistic effect showed low in DEM (4.2 folds) but showed high in PBO (12 folds) and DEF (23 folds).

천적의 성공적인 정착과 산란력은 천적의 능력을 판단하는 중요한 기준이 다. 점박이응애를 방제하기 위해 사막이리응애를 사용함에 있어 천적과 해충사이의 적절한 밀도관리를 통한 해충 발생억제기작이 장기간 유지되는 것이 이상적이라 할 수 있다. 본 연구에서는 실험실에서 강낭콩과 장미, 딸기를 기주로 하여 IOBC quality control guideline에 따라 산란력 및 생존율을 조사하여 점박이응애의 생물적 방제인자로서 사막이리응애의 적용 가능성을 확인하고자 하였다. 온도 20, 25, 30℃, 상대습도 70%RH, 광조건 16L:8D에서 각 작물별 산란력을 조사한 결과, 사막이리응애는 20℃에서 산란수는 적고 생존율은 높았으며, 30℃에서 산란수는 증가고 생존율이 급속히 감소하여 산란력과 생존율 간에 반비례의 관계를 보였다. 작물별로는 온도에 관계없이 장미에서 산란수 및 생존율이 높았으며, 강낭콩과 딸기에서의 산란수 및 생존율은 비슷하였다. 따라서 연중 20~28℃의 온도 조건에서 재배되는 장미에 사막이리응애를 사용했을 때 좋은 방제효과를 얻을 수 있을 것으로 기대되며, 딸기의 경우에도 주간 17~20℃, 야간 10℃ 내외로 서늘하여 사막이리응애의 방사밀도를 조절하면 높은 방제 효과를 기대할 수 있을 것으로 생각된다.

The molecular mechanisms and genetics of abamectin resistance mediated by target site insensitivity in the two-spotted spider mite, Tetranychus urticae, were investigated by comparing two isogenic AbaS and AbaR strains. Cloning and sequencing of full-length cDNA fragments of GABA-gated chloride channel genes revealed no polymorphisms between the two strains. However, sequence comparison of the full-length cDNA fragment of a T. urticae glutamate-gated chloride channel gene (TuGluCl) identified a G323D point mutation as being tentatively related with abamectin resistance. In individual F2 progenies obtained by backcrossing, the G323D genotype was confirmed to correlate with abamectin resistance. Bioassays using progeny from reciprocal crossings revealed that the abamectin resistance trait due to TuGluCl insensitivity is incompletely recessive.

Acquisition of a reference Tetranychusstrains that are completely susceptible to acaricides and retain identical genetic backgrounds to acaricide-resistant strains is an essential step in elucidating mechanisms of resistance. To establish both completely susceptible and acaricide-resistant strains for this purpose, I collected Tetranychus mite populations from various regions in South Korea including both heavily cultivated and remote regions. Suitability as a susceptible or resistant reference strain was tested by determining species identity as Tetranychus urticae along with baseline susceptibility to common acaricides. The majority of mite populations collected from cultivated areas belonged to a monophyletic group of the previously reported green-type T. urticae as determined by mtCOI- and ITS2-based phylogenetic analysis. These strains showed relatively reduced levels of susceptibility to the acaricides tested, suggestive of the development of resistance. Among them, the AbaR strain was classified as a minor group in the T. urticae complex. The UD strain, originally collected from a remote island region, was found to be susceptible to the acaricides tested and generated an independent phylogenetic branch. The UD strain was also considered a minor group in the T. urticae complex. Phenotypic analysis based on morphological characters confirmed that both the AbaR and UD strains were statistically undistinguishable from the major green-type T. urticae. Taken together, I propose that the UD strain be used as a susceptible reference strain as it provides baseline susceptibility to acaricides and a wild-type genetic background for the resistance studies.

The toxicity of 10 plant essential oils to adults of acaricide-susceptible, chlorfenapyr-resistant (CRT-53), fenpropathrin-resistant (FRT-53), pyridaben-resistant (PRT-53), and abamectin-resistant (ART-53) strains of Tetranychus urticae Koch and to female Neoseiulus californicus McGregor was examined using spray or vapor-phase mortality bioassays. In bioassay with the susceptible adults, strong toxicity was produced by lemon eucalyptus, peppermint, citronella Java, thyme red, caraway seed, pennyroyal, and clove leaf essential oils (LC50, 0.0193-0.0327 mg/cm3). The toxicity of these essential oils was almost identical against adults from either of the susceptible and resistant strains, even though CRT-53, FRT-53, PRT-53, and ART-53 adults exhibited high levels of resistance to chlorfenapyr [resistanc ratio (RR), >9140], fenpropathrin (RR, 94), pyridaben (RR, >390), and abamectin (RR,85), respectively. Against female N. californicus was 1.0 to 1.9 times more tolerant than T. urticae to the test essential oils. Thus, these essential oils merit further study as potential acaricides for the control of acaricide-resistant T. urticae populations as fumigants because of their lower toxicity to N. californicus.

전세계적으로 문제가 되는 해충 점박이응애(Tetranychusurticae)를 제거할 목적으로 호주산 식물정유 19가지의 훈증 및 살비 효과를 검토하였다. 점박이응애를 접종한 강낭콩 leaf disc와 식물정유 10 μl/l air 농도로 점적한 filter paper를 밀폐용기 안에 넣고 훈증실험을 하였다. 살비효과는 점박이응애를 접종한 강낭콩 leaf disc를 1,000배 희석한 식물정유 용액에 dipping하여 실험하였다. 훈증 실험 결과 Eucalyptus dives, E. approximans, E. condonocarpa (2ndextract)가 90% 이상의 훈증효과가 있었다. 특히 E. condonocarpa는 100%의 훈증효과를 보였다. 살비 실험의 결과 E. bicostata, E. maidenii, E. sideroxylm, E. approximans, Callistemon viminalis 등 5종의 정유가 67% 이상의 살비효과를 보였다. 이 5종의 식물정유를 100배와 500배로 농도를 높여 실험한 결과, E. maidenii 100배 용액이 100%의 살비효과와 산란 기피효과를 나타냈다. 특히, 91.5%의 훈증 효과가 있던 E. approximans는 100배 희석액에서 83.1%의 살비효과도 나타내었다.

This study was conducted to clear the regional difference in the resistance development of the spirodiclofen 36% WP, an acaricide of tetronic acid class, against two-spotted spider mite, Tetranychus urticae occurred in apple orchard since 2007. Two-spotted spider mite was collected from eight regions in the Chungnam, Chungbuk and Gyeongbuk that were major apple cultivation in Korea. An bioassay was investigated the ovicidal activity to compare with the degree of resistance development of this pest. The managed orchard in Sancheok-myeon, Myeongseo-ri, Chungju was controlled by several different acaricides from 2001 to 2008, and spirodiclofen WP was used for the last seven years. LC50 of spirodiclofen WP was estimated as 19.4 ppm in managed orchard, it showed as high as 2.6-fold (resistance ratio) comparing to those of susceptible strain showed as 7.5 ppm. LC50 of spirodiclofen WP against etoxazole-resistant two-spotted spider mite, gained from Chungbuk National University, was proved in 8.1 ppm. This observation indicates that spirodiclofen WP did not occurred in cross resistance with etoxazole SC. Other two regions in Chungju, the resistance ratio against spirodiclofen WP showed as 2.5- and 2.3-fold, respectively. In Chungnam, Gyeongbuk, it has been limited the resistance ratio under 3-fold, respectively.

The TSSM is one of the most destructive pests on various orchard trees and garden plants. Abamectin resistance mechanisms in two resistant TSSM strains (PTF, ca. 155-fold; AbaR, ca. 3700-fold) were investigated with an emphasis on target site insensitivity mechanism. Detoxification enzyme assays revealed that metabolic factors contributed by EST and/or P450are involved in abamectin resistance. Synergistic assays showed that enhanced detoxification enzyme activity is not enough to account for the high level of abamectin resistance, further suggestive of the involvement of additional resistance mechanism, most likely target site insensitivity. As a putative target site for abamectin, we cloned the cDNA fragments of glutamate-gated chloride channel (Tuglucl) and determined its full length nucleotide sequences. Amino acid sequence comparison among the four strains showed that the Gly323Asp mutation located in the third transmembrane domainis only found in the AbaR strain, suggesting it is likely associated with the target site insensitivity conferring a high level of abamectin resistance.

This study was conducted to compare the effectiveness of single and combination use of N. californicus and N. womersleyi for control of Tetranychus urticae. The experiment was conducted with 5 replications in kidney bean leaf disc (2.5cm diameter) at 25℃, 60-70% RH, a photoperiod of 16:8 (L:D) h. The inoculation ratio was 5:1 for T. urticae:pytoseiidae mite and treatments are: a, N. californicus:T. urticae (4 adult female:20 adult female) b, N. womersleyi:T. urticae (4:20) c, (N. californicus+N. womersleyi):T. urticae ((2+2):20) d, Only T. ulticae (20). T. urticae population became significantly lower in the treatment plots than in the control plot but the higher egg number of T. urticae was observed in the treatment "b" plot than in "a" and "c" plots. In the "c" plot, lower number of N. womersleyi was observed than N. californicus. The result indicates that single use of N. californicus and combination use of N. californicus and N. womersleyi were more effective than single use of N. womersleyi but, there was no significantly difference between single use of N. californicus and combination use of N. californicus and N. womersleyi for control of T. urticae. Also, N. californicus appears to interfere or outcompete N. womersleyi.

This study was conducted to determine whether trichome density affects the oviposition behavior of adult female Tetranychus urticae Koch on host plant leaves. Experiments were conducted with twenty replications on the leaf discs of each plant (Pear, 'Niitaka'; Apple, 'Fuji'; Strawberry, 'Meahyang'; 3cm diameter) at 25℃, 60-70% RH and a photoperiod of 16:8 (L:D) h. One female T. urticae was placed on each disc. The number and locations of laid eggs were recorded at 24 h intervals until T. urticae died. The trichomes were distributed along the midrib of abaxial surface of pear leaves but were evenly distributed on that of apple and strawberry leaves. Eggs were mostly laid along the midrib of pear leaf disc, but eggs were laid not only along the midrib but also randomly over the leaf disc of apple and strawberry. Therefore, it appeared that T. urticae preferred to lay eggs on the specific location where trichomes were densely distributed. Further study is needed to quantify how different distribution patterns of T. urticae eggs on different plant leaves affect the efficacy of predatory mites to control T. urticae.

The objective of this study was to evaluate the effective inoculation position of Neoseiulus californicus for control of Tetranychus urticae on apple branch. This study was conducted under green house conditions. N. californicus was inoculated at different position (Top, Middle and Bottom) of apple branch with a 20:1 ratio (T. urticae:N. californicus). Overall, N. californicus significantly reduced T. urticae numbers in the treatment branches than in the control branch. At 10th day, the T. urticae population was most significantly reduced in the treatment ‘Top’ in which N. californicus were inoculated on the leaf positioned in the top of a branch than in other treatments. At 20th day, most of T. urticae were exterminated in all treatment branches. The daily movement of N. californicus and T. urticae,and their coexistence on apple branch was monitored. Adult N. californicus disappeared from the branch as soon as T. urticae were exterminated in the treatment branches. The result indicates that N. californicus disperse downwards more than upwards in the tree, and the most effective inoculation position for N. californicus for control of T. urticae is the leaves positioned in the top of a branch.

The study was conducted to explore whether environmental differences, in this case the physical characteristics of abaxial leaf surfaces of strawberry cultivars ('Maehyang' and 'Sulhyang' cultivars), affect the functional response of adult female N. californicus preying on immature stages (egg, larva and nymph) of T. urticae. We also evaluated the functional response of N. californicus to eggs of T. urticae at different temperatures (15, 20, 25, 30 and 35℃). We conducted a logistic regression of the proportion of prey consumed as a function of initial prey density to identify functional response types, and used nonlinear squares regression and the random predator equation to estimate attack rates and handling times. The functional response of adult female N. californicus to T. urticae was not influenced by non-glandular trichomes and epicuticular waxes on the abaxial leaf but was affected by temperature. Overall, the functional response of adult female N. californicus exhibited a type 2 functional response to T.urticae. The handling time of N. californicus was highest (1.9970) against T. urticae nymphs. The attack rate did not change much at 15-30℃, but the handling time decreased linearly with increasing temperature. At 35℃, the attack rate was highest (0.1876) and the handling time was lowest (0.9296). The results of this study may be used to evaluate the potential of N. californicus to suppress T. urticae and to estimate parameters for relevant prey-predator models.

This study was performed to investigate the bacterial diversity isolated from the twospotted spider mite and to interpret their correlation between insect bacteria and acaricide resistance. Twospotted spider mite, Tetranychus urticae was used the resistance strains, which developed over eight years to the six acaricides such as abamectin, acequinocyl, bifenozate, etoxazole, fenpropathrin, and pyridaben, respectively. After cultivating the bacteria from body maceration, bacterial colony was selected and identified through 16S rRNA gene sequences. We are identified six genus from Pyridaben resistant strain, five genus from acequinocyl, three genus from abamectin, bifenozate, etoxazole, and two genus from fenpropathrin. However, we could not found correlation between bacterial density and diversity (phylotypes) among these resistant strains. By analyzing the diversity of population microorganisms, fenpropathrin was showed 40% of Cs value (Similarity coefficient) with susceptible strain, however, abamectin and pyridaben were perfectly different (0%) with susceptible strain. It remains to be learned about how microorganisms co-evolutionary developed with their host insect correlating to the resistance and how microorganisms play role in acaricide resistant mite.

Economic injury levels (EILs) and economic threshold (ET) were estimated for the two spider mite, Tetranychus urticae Koch (Acari, Tetranychidae) on greenhouse eggplants. T. urticae density increased until the mid-July and thereafter decreased in all plots where initial density of the mite were different each 0, 2, 5, 10 and 20 adults per plant was innoculated on June 7. Growth variables of were not different among experimental plots but fruit weights were lower in plots with higher initial mite density than in plots with lower initial mite density. Total number of fruits and the number of marketable fruits decreased in plots with higher initial mite density. The rates of yield loss increased with increasing initial mite density, resulting in 0, 3.9, 11.3, 14.5, 22.8% reduction in each of the above plots, respectively. The relationship between initial T. urticae densities and yield losses was well described by a linear regression, Y = 1.085X + 2.474, R² = 0.9659. Based on the relationship, the number of adults per plant which can cause 5% loss of yield was estimated to be approximately 1.8.

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.

To establish a rapid diagnosis method for the monitoring of acaricide resistance in the two-spotted spider mite, Tetranychus urticae, we evaluated the performance of residual contact vial (RCV) method as a routine bioassay for T. urticae by using two widely used acaricides, abamectin and tebupenpyrad. Appropriate concentrations of test acaricides were dissolved in acetone and evenly coated (100 μl) onto the inside wall of a 4-ml glass vial using a rolling machine. The average survival times in untreated control vial was longer than 12 hrs in the absence of food or water regardless of cap being closed or open. Webbing behavior of mites inside the vial, which may interfere with maximum chemical contact, began to be observed from 8 hrs post treatment. The minimum concentrations causing 100% mortality within 8 hrs posttreatment in a susceptible strain of T. urticae were determined to be 30 and 60 ppm in abamectin and tebupenpyrad, respectively. Dose-response curve was significantly affected by temperature in both acaricides, in which the knockdown rate increased greatly as temperature increased. The endpoint mortality at 6-8 hrs posttreatment, however, was not significantly affected by temperature. Nymphal stage of mites showed more rapid intoxication response than adults but endpoint mortality at 6-8 hrs posttreatment was not substantially different between developmental stages. When compared with the results from conventional spray method, RCV method showed moderate to high correlation coefficients (r=0.51~0.98), suggesting that it is a reliable in determining susceptibility of T. urticae. The vial-coated pesticides were stable at least one year when stored at -20°C as determined by LC-MS/MS analysis. Moreover, there was no significant difference in the bioassay results in repeated experiments with three different persons, indicative of high reproducibility of RCV. The RCV diagnostic kit, when used by farmers on site, should provide crucial and essential information for the selection of most suitable acaricides for different field populations of T. urticae.

The European red mite (ERM), Panonychus ulmi, and the two-spotted spider mite (TSSM), Tetranychus uritcae, are serious mite pests in pome fruit orchards worldwide. Abundance and species composition of spider mites in orchard ecosystem have been changed historically in many countries. To illustrate the cause for the historical changes in species composition between ERM and TSSM is an interesting topic. The abundances of the two mite populations have been largely changed in Korean apple orchards: ERM was dominant until 1970s, TSSM has been dominant from 1980s, and then ERM has increased abundantly in some orchards in recent years (Lee, 1990; Kim and Lee, 2005). In apple orchards in Japan, Amphitetranychus viennensis outbreaks occurred immediately after the use of organophosphates in the early 1950, and then, ERM became dominant species on apple until the 1960s followed by TSSM abundance from the late 1970s to the early 1980; Recently, ERM again increasing in IPMadopted apple orchards (Reviewed in Morimoto et al., 2006). Kishimoto (2002) showed changes in the species composition of spider mites caused by different pesticide spray programs in Japanese pear orchards. Pesticides can become an important factor that affects mite species composition of mites through the process of resistance development and the removal of natural enemies. Pesticide resistance and the removal of natural enemies can explain the outbreak of spider mites in orchards, but do not fully explain the changes in species composition of mites. Morimoto et al. (2006) reported a possible exclusion of ERM by TSSM through interspecific interaction via their web: the complicated web created by TSSM increases the mortality of little webspinning species such as ERM. Morimoto et al. (2006) stated that the change in mite species composition can occur as a result of interspecific association between spider mites via their webs, without pesticide applications or the presence of natural enemies. However, their hypothesis does not explain the dominance of ERM in orchards under lower pesticide pressure. Also, Belczewski and Harmsen (1997) concluded that the application of additional or supplemental amounts of a Phylloplane fungus (Alternaria alternata) to apple leaves enhanced the population growth of TSSM compared to that of ERM. However, this does not explain the dominance of TSSM in orchards under heavy pesticide pressure where Phylloplane fungal population would be lowered by fungicides, and the dominance of ERM in unsprayed orchards where Phylloplane fungal population would be abundant because of no fungicide application. The change in species composition among spider mites can not be projected with any single factor. It is required to examine all possible combinations of factors involving. Until now the change in abundance between ERM and TSSM has not been examined comprehensively. Therefore, we examine possible changes in population abundance between REM and TSSM with some assumptions. Also, case studies that deal with long-term and short-term changes between the two mites are presented.

The two-spotted spider mite, Tetranychus urticae Koch, is one of major pests in greenhouse strawberry. Two predator mites, Neoseiulus californicus (McGregor) and Phytoseiulus persimilis (Athias-Henriot), have been widely used for control of T. urticae because they have good functional and numerical responses and searching behaviors. The study of single species releasing and combined releasing of two predatory mites, N. californicus and P. persimilis, was conducted on connected strawberry leaves. The experiments were run under laboratory conditions, 24±1oC, 50-65% RH, and a photoperiod of 16:8 (L:D) h. The excised leaf disk (diameter 3cm) of two strawberry varieties – Maehyang, Sulhyang– were placed upside down on a water-saturated cotton pad in an aluminum pan (width × length 17.4 × 21.5 cm). Twenty leaf disks were placed on each experimental set and the disks (width × length 4×5 cm.) were connected with each other for dispersing of T. urticae and its predatory mite. There were four different experiments – two strawberry varieties and two treatments (releasing single predatory mite, releasing two predator mites). The experiment sets were covered with plastic cage to protect from invading other insects and mites. All life stages of T. urticae and predatory mites were recorded until all mites were vanished. The data were transformed by ln (x+1). Repeated-measures analysis of variance was used to compare the temporal variation in the overall T. urticae and predatory mite density. The average number of T. urticae per leaf arena was significantly different among treatments in Sulhyang (Treatment, df=3, 196, F=17.86, P=0.0001; Time, df=6, 1176, F=47.76, P=0.0001; Time ×Treatment, df=18, 1176, F=22.06, P=0.0001) and in Maehyang (Treatment, df=3, 196, F=42.07, P=0.0001; Time, df=6, 1176, F=64.51, P=0.0001; Time x Treatment, df=18, 1176, F=24.19, P=0.0001). When N. californicus was introduced to P. persimilis system with diminishing prey, P. persimilis population increased more rapidly than N. alifornicus but P. persimilis was displaced by N. californicus. In single or combined releasing system, N. californicus persisted longer after prey depletion than P. persimilis. We examined population growth of P. persimilis and N. californicus in single and combined predatory mite released system with diminishing prey.