Kijong Cho

Unbiased estimation of greenhouse whitefly, Trialeurodes vaporariorum, mean density using yellow sticky trap in cherry tomato greenhouses

The spatial distribution of the count of adult greenhouse whiteflies, Trialeurodes vaporariorum (Westwood), on yellow sticky traps was analyzed using Taylors power law and spatial autocorrelation statistics in the cherry tomato greenhouses from 1998–1999. Samples were collected weekly using a cylindrically shaped yellow sticky trap placed in a 5 by 8 grid covering 0.10–0.15 ha in each of five cherry tomato greenhouses. Taylors (1961) power law indicated that counts of T. vaporariorum on traps were aggregated within greenhouses. Spatial autocorrelation analysis showed that trap catches were similar (positively autocorrelated) to a distance of 12.5 m, and then dissimilar (negatively autocorrelated) at >12.5 m. Autocorrelation‐lag plots showed a globally significant spatial relation in 34 of 57 sample‐weeks according to Bonferronis approximation. The presence of this spatial relation was not related to the changes of mean density. Trap counts at the second lag distance (12.5–25 m) showed little spatial autocorrelation and tended to be the most spatially independent. A fixed‐precision‐level sequential sampling plan was developed using the parameters from Taylors power law. The presence of spatial dependency in data sets degraded the sampling plans precision relative to performance in data sets lacking significant spatial autocorrelation. Therefore, to obtain an unbiased mean density of T. vaporariorum per greenhouse, sticky traps should be placed at least >12.5 m apart to ensure that they are spatially independent.

Spatial distribution and sampling plans for Thrips palmi (Thysanoptera: Thripidae) infesting fall potato in Korea.

Abstract The spatial distribution of adult and immature Thrips palmi Karny on fall potato, Solanum tuberosum L., on Cheju Island, Korea, was studied over a 2-yr period by visually inspecting potato leaves. The majority of thrips collected from the leaves were observed in the top one-third of the plant. The within-field spatial patterns of adults and immature thrips were aggregated. The slopes and intercepts of Taylor’s power law did not differ among adults and immature thrips. A fixed-precision-level sampling plan was developed using the parameters from Taylor’s power law and was tested with resampling simulations using eight independent data sets. Over a wide range of densities, the simulation demonstrated that actual sampling precision (d = SEM/mean) values at d = 0.25 averaged <0.24 in all cases. A binomial sampling plan for estimating mean density was developed using an empirical model evaluated at tally thresholds (the minimum number of insects present before a leaf is considered infested) of one, three, five, and eight thrips per leaf. Increasing sampling size had little effect on the precision of the estimated mean regardless of tally threshold (T). However, increasing T had a dramatic effect on precision. The best tally threshold for estimating thrips density based on the applicable density ranges and the precision of the model was T = 5. A binomial sampling plan with a tally threshold of five and a fixed sample size of 30 leaves should be an effective replacement for enumerative counts when thrips average <10 per leaf.

A model for the temperature-dependent developmental rate of Sitophilus oryzae L. (Coleoptera: Curculionidae) on rice

Abstract The development of Sitophilus oryzae (L.) in relation to temperature was studied on rice. The total developmental periods on rice were similar to those reported on wheat. A model constructed by combinging those of Logan et al. (1976) and Wollkind et al. (1978) provided a good description of this weevils development throughout the range of lower and upper threshold temperatures. The lower and upper threshold temperatures for overall development of the weevil were estimated to be 15.0° and 34.1°C.

Endosulfan-Induced Biomarkers in Japanese Rice Fish (Oryzias latipes) Analyzed by SELDI-TOF-MS

The objective of this study was to find and validate estrogen-related biomarkers from plasma proteins in Oryzias latipes after exposure to an estrogen disrupting compound, α-endosulfan. The acute toxicity of α-endosulfan on O. latipes after 96 h of exposure was 13.72, 16.18, and 22.18 μg L-1 for the LC10, LC20, and LC50 values, respectively. To confirm estrogenic disturbance by α-endosulfan, the expression level of vitellogenin in the liver of male fishes was measured at the LC10 value, and it was found to be significantly different from the reference group, confirming the estrogenic effect of endosulfan in this concentration range. Proteinchip® array techniques using a weak cation exchange (CM10) and a strong anion exchange proteinchip (Q10) in conjunction with surface-enhanced laser desorption/ionization time of flight mass spectrometry (SELDI-TOF-MS) were used to determine plasma proteins of O. latipes differently expressed in response to endosulfan exposure at LC10 and LC20 concentrations. Analysis of protein profiling of the male fish exposed to α-endosulfan detected 48 significantly different protein peaks and the proteins at m/z 2819, 8462, 8860, and 9462 were significantly different (p<0.05). The protein peaks at m/z 2819, 8860, and 9462 were up-regulated and the peak at m/z 8462 was down-regulated. Therefore, these four differentially expressed proteins could be used as biomarkers to rapidly determine a possible risk of endosulfan on aquatic ecosystems, although these are not necessarily produced as a result of endocrine disruption.

Combined effects of water quality parameters on mixture toxicity of copper and chromium toward Daphnia magna.

In this study, a central composite design (CCD) was employed to evaluate the combined effects of pH, hardness and dissolved organic carbon (DOC) on the toxicity of a mixture of Cu(II) and Cr(VI) toward Daphnia magna. Overall, the results showed that increases in pH, hardness and DOC concentration led to decreased mixture toxicity of Cu(II) and Cr(VI) by reducing the concentrations of toxic species such as Cu(2+) and HCrO(4)(-). In addition, empirical models for the prediction of 24-h and 48-h mortalities of D. magna were developed and validated by using three different sources of dissolved organic matter (DOM). Because the DOMs had different Cu(II)-binding capacities, the empirical models were revised using the ligand concentration of DOMs instead of the DOC concentration; however, the prediction capability of these models did not differ significantly. These results suggest that it is not likely that the chemical property of DOM is important for prediction of the mixture toxicity of Cu(II) and Cr(VI) toward D. magna when the ligand concentration of DOMs greatly exceed the Cu(II) concentration.

Evaluation of resistance pattern to fenpyroximate and pyridaben in Tetranychus urticae collected from greenhouses and apple orchards using lethal concentration-slope relationship

This study aimed to monitor the present and future developments of the resistance of Tetranychus urticae Koch to fenpyroximate and pyridaben, using the relationship of the LC50 and slope of the concentration-mortality line in a probit model, for the provision of reliable resistance management tactics. Tetranychus urticae populations were collected from 16 commercial greenhouses, where various crops were cultivated, as well as from 10 apple orchards throughout Korea. The resistance to fenpyroximate and pyridaben of each population was estimated by calculating the median lethal concentration (LC50), resistance ratio (RR) and slope of the concentration-mortality regression. Most of the greenhouse populations exhibited moderate levels of resistance, whereas the apple orchard populations showed only low levels, indicating that T. urticae populations in greenhouses were more strongly selected than those in apple orchards. Four population groups were established based on either the habitats (greenhouse and apple orchard) or acaricides (fenpyroximate and pyridaben). To test the hypothesis, “the slope is greatest at low and high levels of resistance,” the slopes were regressed as a function of the LC50, and fitted to a polynomial regression. The polynomial regression model explained this relationship well for the four population groups (p < 0.05), indicating that the development of resistance toward fenpyroximate or pyridaben was consistent with the gradient. A laboratory selection study agreed with the results from both acaricide field populations. These results suggest that the gradient was a good indicator of the susceptibility of T. urticae to genetic variations, which was related to the LC50. The application of these findings is also discussed in relation to the resistance management of T. urticae.

Biomarker discovery and proteomic evaluation of cadmium toxicity on a collembolan species, Paronychiurus kimi (Lee)†

The goal of this study was to identify promising new biomarkers of cadmium by identifying differentially expressed proteins in Paronychiurus kimi after exposure to cadmium. Through proteomic analysis of P. kimi using 1‐D PAGE and nano‐LC‐MS/MS, 36 downregulated proteins and 40 upregulated proteins were found. Some of the downregulated and upregulated proteins were verified by LC‐MS/MS analysis after 2‐D PAGE. Downregulated proteins in response to cadmium exposure were involved in glycolysis and energy metabolism, chaperones, transcription, reproduction, and neuron growth. In contrast, proteins involved in glycolysis and energy production, neurogenesis, defense systems response to bacteria, and protein biosynthesis were upregulated in cadmium‐treated collembolans. Cubulin may be a potential biomarker for the detection of cadmium in P. kimi since this biomarker was able to low levels (3.5 mg/kg) of cadmium. The 14‐3‐3 ζ was also found to be a potential biomarker for the detection of medium levels (14 mg/kg) of cadmium. Collembolans may be an alternative tool to humans because many collembolans proteins show a high homology to human proteins.

Predicting the potential geographic distribution of Thrips palmi in Korea, using the CLIMEX model

Thrips palmi Karny, melon thrips was introduced and first recorded in 1993 in Korea. This species has become a serious pest of vegetable and ornamental crops. The CLIMEX simulation was applied to T. palmi to predict its potential geographic distribution in Korea under the Representative Concentration Pathway (RCP) 8.5 climate change scenario. In the CLIMEX simulation, the ecoclimatic index was calculated, and compared in each simulated year and each simulated location. The map comparisons show good agreements between simulated and present distributions of T. palmi, indicating that the CLIMEX model has promising potential for prediction of future distributions of this species in Korea. In the near future, until the year 2020, all the western and eastern parts of Korea show favorable to marginal suitability for T. palmi populations in the fields. After the year 2040, potential distributions shift from no persistence to favorable for establishment and persistence from coastal to interior regions of the Korean peninsula, except for a north‐eastern interior region which is the northernmost part of a high mountainous (Baekdu‐Daegan) area in Korea. Based on the simulation results, the geographical distribution of T. palmi will expand over its current weather restrictions in the near future under a severe climate change scenario. Thus, pest management measures and strategies should be re‐evaluated in Korea, and should include further studies on interspecific competition and ecosystem changes due to climate changes.

Response surface model for predicting chronic toxicity of cadmium to Paronychiurus kimi (Collembola), with a special emphasis on the importance of soil characteristics in the reproduction test

A central composite design (CCD) was employed to investigate the effects of organic matter (OM) content and soil pH on the reproduction, and chronic toxicity (28-d EC(50-reproduction)) of cadmium for Paronychiurus kimi after 28days exposure in a standard artificial soil. Two statistical models were developed, one describing reproduction in control artificial soils as a function of OM content and pH, and the other describing cadmium toxicity to the same soil parameters. In the reproduction model, pH was the most important factor, followed by two quadratic factors of OM(2) and pH(2). The parameter pH alone could explain 75.5% of the response variation. The reproduction model will allow us to predict a mean reproduction in the non-treated control soils that contain various combinations of OM content and different pH values. In the chronic toxicity model, only the linear factor of the OM content and pH significantly (p<0.05) affect cadmium toxicity, which explains the 78.9% and 14.9% of total response variance, respectively. Therefore, the final polynomial regression describing the chronic toxicity of cadmium to P. kimi is as follows: predicted 28-d EC(50) of cadmium (mgkg(-1))=-21.231+2.794 x OM+4.874 x pH. The present study show that soil characteristics, which can alter the toxicity of cadmium, can also act as stressors themselves in regards to the reproduction of P. kimi. Based on the physico-chemical characteristics of the test media, the response surface model developed in this study can be used to provide initial toxicity information for cadmium within a region of interest in terms of OM content and pH, and may lead to more scientific based risk assessment for metals.

Use of covariates in Taylor’s power law for sequential sampling in pest management

In pest management, the pest density within a group of plants needs to be estimated for taking timely actions, such as spraying pesticides or releasing natural enemies. Taylor’s power law is widely used for identifying the aggregation patterns of the pests and designing a sequential sampling plan to estimate the pest mean density. The conventional estimates given by Taylor’s power law do not consider potential density differences due to various covariates, but focus only on the relationship between the sample means and the variances.In this article, we develop a new sequential sampling stop line based on Taylor’s power law by using quasi-likelihood with covariate effects. The simulation results show that the proposed estimators are better than the conventional estimators in terms of mean squared error. For validation and evaluation of the sampling stop line given by the proposed estimator, we use RVSP software in which actual observations are randomly and iteratively sampled until the total number of a pest reaches the stop line. We demonstrate both types of sequential sampling stop lines, those based on the conventional method and those based on the new method, for the population density of spider mites on glasshouse roses.