Understanding the occurrence patterns of forest pests is fundamental for effective forest management from both economic and ecological perspectives. Here, we review the history of the occurrence patterns and causes of outbreaks and declines of pests in Korean pine forests over the last 50 years. During this period, the major pests of pine forests in Korea have shifted from pine caterpillar (Dendrolimus spectabilis Butler) to the pine needle gall midge (PNGM, Thecodiplosis japonensis (Uchida and Inouye)) and finally to pine wilt disease (PWD) caused by the pine wood nematode (Bursaphelenchus xylophilus (Steiner and Buhrer) Nickle). Outbreaks of pine caterpillar, a native species in Korea, have been recorded as far back as 900 years, and it was the most relevant forest pest in Korea until the 1970s. The decline of its importance has been attributed to reforestation and higher levels of subsequent natural enemy activity. The PNGM is an invasive species, first discovered in Korea in 1929, that became widely distributed by 1992 and the major forest pest in the 1980s and 1990s. A suite of parasitic wasps attacking the PNGM contributed at least partially to the decline of PNGM densities. Following the decline of the PNGM, damage from PWD has increased since 2003. These shifts in major forest pests might be related to changes in forest composition and interactions among forest pests. Therefore, a new management strategy for controlling forest pests is required to mitigate the decline of pine forests in Korea.

One of the subspecies of the Eurasian spongy moth, Lymantria dispar asiatica, is a destructive forest pest in native regions and also an important quarantine pest in non-native regions. Its polyphagous nature, together with occasional outbreaks, may seriously threaten ecosystems and result in costly management programs. In this study, we examined the effect of chilling temperatures (−12, −6, 0, 6, and 12 °C) during the diapause phase on the survival and post-diapause development of L. d. asiatica eggs, collected before winter, in order to characterize their thermal response. The eggs were exposed to treatment temperatures for 100 days, followed by 25 °C incubation to determine their survival and development time. The eggs hatched in all the treatments, indicating that all the examined conditions could partly or sufficiently satisfy the thermal requirement for eggs to enter post-diapause development. However, exposure to chilling temperatures significantly affected both the survival and development times of overwintering eggs in a given temperature range. The survival rates declined at −12 °C, and the development rates accelerated as the chilling temperature increased. This information could offer clues for the assessment of the outbreak potential in native regions and the possibility of range expansion in non-native regions through the consideration of winter conditions that favor L. d. asiatica egg hatching and their subsequent development.

Ips subelongatus is a species of bark beetle experiencing population outbreaks in Korea. In this study, a predictive model and empirical prediction were used to forecast the spring flight of these beetles in Japanese larch forests. The number of beetles caught in pheromone traps was investigated in larch forests thinned in 2009, 2010, 2012, or 2013. Data from the sites thinned in 2009, 2010, or 2012 were used in the predictive model based on a degree-day model that was validated using data from the site thinned in 2013. The lower threshold temperature for flight (LTF) and a thermal sum for the spring flight of I. subelongatus were estimated. The empirical prediction that beetles initiate their flight when daily maximum temperatures reach 16 or 20°C was tested using daily maximum temperature and the beetles caught. The LTF was estimated as 5.97°C, with 42.95 degree-days required for initiation of spring flight. The median flight dates were estimated with a discrepancy from 1 to 3 d by the predictive model. Using the empirical prediction, differences between the day when daily maximum temperature reached 16 or 20°C and flight peak days ranged from 4 to 45 d. These results demonstrate that the predictive model is more suitable than the empirical prediction for predicting the spring flight of I. subelongatus. Overwintering I. subelongatus adults seem to need to gain a determined thermal sum before initiating spring flight rather than merely waiting for the daily maximum temperature to exceed a critical temperature.

We conducted an experiment to confirm the passability of chironomid larvae (Glyptotendipes tokunagai) in granular activated carbon (GAC) used in water treatment plants. After injecting larvae at different growth stages (first through fourth instars) into circular columns filled with GAC, the number of individuals and their locations within the GAC columns were recorded after 168 h. We found that more than 80% of the injected larvae in the first instar and 3.3% in the second instar passed, whereas none from the third and fourth instars had passed through the column. The second instar larvae were evenly distributed within the column, whereas the third and fourth instar larvae were mostly distributed within 10 cm of the upper layer of the GAC. Our results demonstrate the passability of chironomid larvae in GAC and can be used as basic information for water quality management in water treatment plants.

Ecological rules such as Bergmann’s rule and the temperature–size rule state that body-size decline is a universal response to warm temperatures in both homeotherms and poikilotherms. In the present study, we investigated the biological responses of Nannophya koreana, an endangered dragonfly species in Korea, by comparing body size in two habitats with large differences in water temperature, Mungyong-si (MG, terraced paddy fields) and Muui-do (MU, a mountainous wetland). To conserve the dragonfly populations, the collected larvae were photographed and released, and their head widths and body lengths were measured. There was no difference in the annual mean air temperature and precipitation between the two sites; however, the annual mean water temperature was substantially lower in MU than in MG. There was little difference in larval head width between the two sites; however, body length in the MU population was smaller than that in the MG population. Larval growth rate per 100-degree-days was 0.75 mm for MG and 1.16 for MU. The relationship between temperature and body size of N. koreana larvae showed opposite trends to Bergmann’s rule and the temperature–size rule. Since the larval growth period during a year in MU was shorter than that in MG, the MU population potentially exhibits a higher growth rate as a mechanism of compensating for the low water temperature. Our study established the relationship between temperature and body size of N. koreana in two wetlands that had an obvious difference in water temperature despite being geographically close. The results highlight the importance of considering detailed factors such as habitat type when studying the temperature–size responses of organisms.

Korean oak wilt (KOW) is vectored by the beetle Platypus koryoensis (Murayama) (Coleoptera: Curculionidae), a native species of Korea, whose dispersal distance is a key factor determining the spread of damage by KOW. To estimate dispersal distance at stand level, we conducted a markreleaserecapture (MRR) experiment and validated its results using an independent data. Sticky traps were attached to the trunks of oak trees up to 48.8 m from the release point. Beetles were marked with different three fluorescent powders by date and released, and the number of recaptured beetles was counted 90 min after release. To validate the flight distance, annual mean dispersal distance of P. koryoensis population was analyzed using GPS coordinates of oak trees with the symptom of KOW recorded in the field from 2012 to 2014 in independent oak stands that have been damaged by KOW since 2012. The beetles were recaptured only on the day they were released, suggesting that the beetles only make one flight. The percentage of recaptured beetles was 6.0 1.6%. The mean dispersal distance was 18.0 1.3 m, and more than 85% of recaptured beetles were caught within 25 m. Annual movement distances in infested stands were 24.1 and 19.9 m from 2012 to 2013 and 2013 to 2014, respectively, similar to the dispersal distance obtained from our MRR experiment. Our results showed that the dispersal distance of P. koryoensis estimated by MRR is a useful process for predicting the spread of areas damaged by KOW.