Yeong-Jin Chung

Use of an Artificial Neural Network to Predict Population Dynamics of the Forest–Pest Pine Needle Gall Midge (Diptera: Cecidomyiida)

Abstract The backpropagation algorithm in artificial neural networks was used to forecast dynamic data of a forest pest population of the pine needle gall midge, Thecodiplosis japonensis Uchida et Inouye, a serious pest in pine trees in northeast Asia. Data for changes in population density were sequentially given as input, whereas densities of subsequent samplings were provided as matching target data for training of the network. Convergence was reached, generally after 20,000 iterations with learning coefficients of 0.5–0.8. When new input data were given to the trained network, recognition was possible and population density at the subsequent sampling time could be predicted.

Temperature-dependent post-diapause development and prediction of spring emergence of the pine needle gall midge (Dipt., Cecidomyiidae)

Abstract:  We determined the influence of temperature on post‐diapause development of overwintered Thecodiplosis japonensis Uchida et Inouye (Dipt., Cecidomyiidae) under various treatments (12, 15, 18, 21, 24, 27 and 30°C) in an effort to predict its spring emergence. Survival and developmental period for the overwintered larvae and pupae were significantly influenced by temperature. Linear and nonlinear regression models quantitatively described temperature‐dependent development and survival of T. japonensis. The survival models exhibited right‐skewed bell shape patterns for all stages, indicating a more detrimental impact on survival at high temperatures. Theoretical optimum temperatures with highest survival were 22.3, 24.0 and 24.0°C for the overwintered larvae, pupae and total post‐diapause development (the larvae to adults) respectively. Pupal mortality was higher at all temperatures than larval mortality and the suitable range of temperature for pupae was narrower than that of larvae. The nonlinear Briere model estimated that optimum temperatures with the fastest development were 29.1°C for larvae, 27.6°C for pupae and 27.0°C for larvae to adults. In a linear model, the lower threshold temperatures were 5.1, 7.1 and 5.9°C for larvae, pupae, and larvae to adults respectively. A predictive degree‐day model was developed using trap catches of T. japonensis adult emergence during 1991–1995. The model accounted for 84.6% of year‐to‐year variation in adult emergence and predicted accurately the median emergence time in 1996.

Hazard ratings of pine forests to a pine wilt disease at two spatial scales (individual trees and stands) using self-organizing map and random forest

Pine wilt disease (PWD) caused by the pine wood nematode is the most serious global threat to pine forests. Hazard ratings of trees and forests to pest attacks provide important information to efficiently identify current or future hazardous conditions. However, in spite of the importance of hazard ratings for managing PWD, there are few studies on hazard ratings in this system. In this study, we evaluated the hazard ratings of pine trees and pine stands to PWD by considering environmental factors at the level of the stand and the individual tree. Our results showed that trees with larger diameter at breast height (DBH) showed a higher risk rate than those with smaller DBH, indicating that large trees have an increased probability of exposure to vector beetles because they are tall and have a large crown volume. We also found that reduced tree vigour could be related to susceptibility to PWD. In pine stands, geographical factors showed a high correlation with the occurrence of PWD. PWD occurrence was rare at high altitudes, but was more common on steep and south-facing slopes. These patterns were consistently observed in the results from 2 computational approaches: self-organizing map (SOM) and random forest models. The combination of SOM and random forest was effective to extract ecological information from the dataset. The SOM efficiently characterized relations among variables, and the random forest model was effective at predicting ecological variables, including the hazard rating of trees to disturbances.

Seasonal changes of functional groups in coleopteran communities in pine forests

Fauna assemblages reflect their habitat relating to ecological function in an ecosystem. The functional groups are concerned with how a resource is processed by different species to provide a specific ecosystem service or function. We elucidated seasonal changes of coleopteran functional groups in forests, and evaluated their ecological roles related to available food resources. Coleopteran communities were collected weekly or biweekly using Malaise traps at nine study sites in Japanese red pine forests in Korea from late June to September 2005. Compositions of the functional groups were compared at the different sites and at sampling times with respect to taxa richness and abundance. Cluster analysis and non-metric multidimensional scaling were used to characterize spatial and temporal changes of functional groups. Herbivores and dead/live wood feeders regulating primary production in the pine forests were the dominant coleopteran groups in July, followed by detritivores and predators that dominated from July to August, resulting from the accumulation of detritus. Then, fungivores became dominant due to increased fungal biomass in the forest. Seasonal changes of coleopteran functional groups shifted from regulators of primary production to regulators of decomposition, reflecting their available food resources. In addition, abundance of detritivores and predators were dependent on total abundance of coleopterans, suggesting that these two groups reflect their habitat condition.

Geographical variation in the population dynamics of Thecodiplosis japonensis: causes and effects on spatial synchrony

Geographical variation in population dynamics of a species offers an opportunity to understand the factors determining observed patterns of spatial dynamics. We evaluated the spatial variation in the population dynamics of the pine needle gall midge (PNGM), Thecodiplosis japonensis, which is a severe insect pest in pine forests in Korea, and studied the influences of weather factors that could affect its population dynamics. Results revealed that PNGM population dynamics were classified into five clusters based on the analysis of autocorrelation function and self-organizing map, which is an artificial neural network. We also quantified spatial synchrony in the population dynamics of PNGM using the nonparametric covariance function. Variation in spatial synchrony was strongly related to differences in maximum temperature and precipitation in Random Forest analysis, suggesting that the synchrony in PNGM population dynamics is largely the result of the Moran effect. In addition, spatial differences in population dynamics could be influenced by transient process of synchronization following invasion. Finally, the present results indicate that differences in population dynamics can be induced by interactions among several factors such as maximum temperature, precipitation, and invasion history of species.

Biological Characteristics of Sclerodermus harmandi (Hymenoptera: Bethylidae) Parasitized on Cerambycid

This study was performed to investigate the immature development period, fecundity, emergence rate and sex ratio of Sclerodermus harmandi against different host insects, Monochamus alternatus, M. saltuarius and Psacothea hilaris. Full grown larvae and pupae of host insects were provided with foods. The mean larval period of S. harmandi female was days in larvae and pupae of M. alternatus, days in M. saltuarius, and days in P. hilaris, respectively. S. hilaris adults were emerged at days in female and days in male after pupation when hosted M. alternatus pupa. Development period in male showed shorter one day than in female. Success rate of oviposition against different hosts was higher as 98.6 and 97.5% on full grown larva and pupa of M saltuarius. Emergence rate was higher as 90.1 and 87.3% on M. saltuarius larvae and pupae. Sex ratio of emerged S. harmandi adults was approximately 10:1 (Female : Male), females showed higher emergence rate than males. The period until first oviposition after emergence in S. harmandi female was the shortest in days on M. saltuarius pupa. When three females of S. harmandi were inoculated on M. saltuarius larva, the number of laid eggs was the highest per female.

Population dynamics of Thecodiplosis japonensis (Diptera: Cecidomyiidae) under influence of parasitism by Inostemma matsutama and Inostemma seoulis (Hymenoptera: Platygastridae)

Abstract To understand influence of two species of parasitoids on host population dynamics, adult population dynamics of pine needle gall midge (PNGM), Thecodiplosis japonensis and two species of parasitoids, Inostemma matsutama and Inostemma seoulis were observed using emergence traps from 1986 to 2005. Density of PNGM decreased after outbreaks in 1986 and 1987 and showed density-dependent regulation. Relationships between density of PNGM and its parasitoids were linear except the period of outbreak regardless of parasitoids species. Relationships between host density and parasitism of I. matsutama and I. seoulis were density-independent and inverse density-dependent, respectively. I. seoulis was the dominant parasitoid against PNGM. Interspecific competition between two parasitoids was not strong and temporal niche segregation between two parasitoids was a possible mechanism for coexistence of two parasitoids. The parasitoid complex responded to changes in host density more sensitively than single parasitoid species. These results suggested that two parasitoid can stabilize PNGM population density without strong negative effects on each species of parasitoids.

Molecular biological characterization of bursaphelenchus xylophilus and bursaphelenchus mucronatus in Korea

Pine wood nematode (PWN), Bursaphelenchus xylophilus, is a causal organism to induce pine wilt disease (PWD) in many varieties of pine trees. PWD was first introduced to Korea in 1988 but, the damage has been dramatically increased since 2000. Recently PWD is newly reported in Korean pine tree (Pinus koraien‐sis) and is considered one of the most important forest diseases in Korea. Fifteen isolates of B. xylophilus, 2 isolates of B. mucronatus, and 6 unidentified Bursaphelenchus spp. were collected from different geographical locations and hosts in Korea. All the isolates were cultured in fungal medium and nematodes were harvested for further experiment. First, all the isolates were characterized by both ITS and D2D3 rDNA sequence analysis. Template DNA was prepared by DNA extraction from single female nematode. ITS and D2D3 region were amplified by PCR and followed by cloning and sequence. As a result, all the sequences of ITS and D2D3 from B. xyophilus isolates were identical and there is no intraspecific variation. However, 2 genotypes of B. mucronatus were found, which one from P. thunbergii was East Asian type and the other one from P. koraiensis was European type. ITS‐RFLP phenotype was also proposed to discriminate different species and genotypes and 5 enzymes, Hinf I, Alu I, Msp I, Hae III, and Rsa I. were selectively treated.