Cold hardiness is an important trait for insects, that enables them to survive during the winter and develop in the next season, and to extend their range. Lycorma delicatula (White), which became an important sporadic pest in grapevines and some other fruit trees, has spread rapidly to the most of regions in South Korea. This study was conducted to determine the cold hardiness of overwintered L. delicatula eggs according to geographical variation. We collected overwintering eggs in the five sites, Chuncheon, Suwon, Yeongdong, Gunsan, Daegu, on 22~25th Feb. in 2011. We treated eggs to combinations of different temperatures (-15℃, -20℃, -25℃) and exposure time (12hr, 24hr, 3days, 5days, 7days) after chilling them for 24~26 days at 5℃. And then, they were kept in the room temperature. We only analysed three sites of Suwon, Gunsan and Daegu, because of very low hatching rate at Chuncheon and Yeongdong. There were significant effects of time (F=36.97 d.f.=4 P<0.0001), sites (F=17.28 d.f.=2 P<0.0001), and the interaction of time and temperature (F=5.77 d.f.=5 P<0.0001) at -15℃. At -20℃, eggs hatched only at 12hr and 24hr of exposure treatment. All eggs treated at -25℃ failed to hatch. It appears that -25℃ is around the critical temperature.

We studied to develop a forecasting model to predict the hatching time of overwintered eggs of Lycorma delicatula. We collected overwintering egg masses on 1st February, 17th February and 4th March. After chilling them at 5℃ for 15 days, development of eggs was investigated at six constant temperature (35, 31, 27, 23, 19, 15℃). The hatching rate of egg was highest at 23℃ (87.88±19.32%) followed by 19℃ (87.71±21.47%), 27℃ (75.96±24.82%), and 31℃ (30.92±24.81%). Eggs did not survive at 35℃. The developmental duration of eggs was 39.47±2.24, 22.96±3.25, 17.56±1.58 and 12.15±6.29, at 19, 23, 27 and 31℃, respectively. The egg developmental rate was described with a linear model (eq. Y=0.0034X-0.0364 (r=0.9649)) between 19℃ and 31℃. The lower developmental threshold temperature was 10.71℃ and effective accumulated temperature for egg development was 286.40 Degree days.