Ecological Responses of Nannophya koreana (Odonata: Libellulidae) to Temperature: Following Converse Bergmann's Rule.

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.

Passability of Chironomid Larvae in Granular Activated Carbon.

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.

Forecasting Spring Flight of Ips subelongatus (Coleoptera: Curculionidae: Scolytinae) in Japanese larch Larix kaempferi (Pinales: Pinaceae) Forests in the Republic of Korea.

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.

Estimating Flight Distance of Platypus koryoensis (Coleoptera: Curculionidae) by Mark-Release-Recapture and Its Validation by Field Observation.

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 mark-release-recapture (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.

A Model for Predicting Spring Emergence of Monochamus saltuarius (Coleoptera: Cerambycidae) from Korean white pine, Pinus koraiensis.

Monochamus saltuarius Gebler is a vector that transmits the pine wood nematode, Bursaphelenchus xylophilus, to Korean white pine, Pinus koraiensis, in Korea. To reduce the damage caused by this nematode in pine forests, timely control measures are needed to suppress the cerambycid beetle population. This study sought to construct a forecasting model to predict beetle emergence based on spring temperature. Logs of Korean white pine were infested with M. saltuarius in 2009, and the infested logs were overwintered. In February 2010, infested logs were then moved into incubators held at constant temperature conditions of 16, 20, 23, 25, 27, 30 or 34°C until all adults had emerged. The developmental rate of the beetles was estimated by linear and nonlinear equations and a forecasting model for emergence of the beetle was constructed by pooling data based on normalized developmental rate. The lower threshold temperature for development was 8.3°C. The forecasting model relatively well predicted the emergence pattern of M. saltuarius collected from four areas in northern Republic of Korea. The median emergence dates predicted by the model were 2.2-5.9 d earlier than the observed median dates.

Life history and emergence pattern of Cloeon dipterum (Ephemeroptera: Baetidae) in Korea.

Cloeon dipterum (L.) (Ephemeroptera: Baetidae), the common wetland mayfly, emerges and oviposits every season, except winter, and has overlapping generations in the temperate region. We investigated the life history of C. dipterum associated with drought. Field experiments and sampling were conducted in a wetland (25 by 80 m) located in central Korea. Larvae were sampled weekly within two habitat types (a large, deep wetland and a small, shallow wetland) using a dredge sampler, and adults were sampled every 2 d with cube emergence traps, from July 2011 to September 2012 (except winter). C. dipterum had an extended emergence period from late April to early October with four peaks: early May, mid-June, July, and August/September. When the water depth was shallow because of drought, emergence was suppressed and delayed. The accumulated degree-days and body length of the overwintering cohort that emerged in spring 2012 were markedly larger and longer than those of other cohorts. Adults emerged intensively around sunset. C. dipterum has a multivoltine life cycle with four cohorts per year; its life history and population density can be changed by natural disturbances such as drought and fish predation.