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

Abstract

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 degrees C was tested using daily maximum temperature and the beetles caught. The LTF was estimated as 5.97 degrees 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 degrees 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 1. 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.