Diprion hani Smith and Cho was first reported as a new species from South Korea in 2007. Major outbreaks occurred in September 2007. Outbreaks were restricted geographically to only three inland areas of central Korea where had previously been reforested with Korean white pine, Pinus koraiensis Seib. & Zucc. The outbreak areas were approximately 50 km in diameter. The sawfly populations decreased drastically in 2008. Environmental factors of the outbreak sites were investigated as a first step to characterize the sites and to understand the population dynamics of the sawfly. During the outbreak in 2007, the average temperature of the sites were 1.3℃ higher than the 30 years average, and the annual precipitation was 384 mm higher than the average from 1971 to 2000. In addition, Monodontomerus dentipes (Dalman), a well-known torymid parasitoid of many sawflies, is reported as a gregarious cocoon parasitoid of D. hani.