An outbreak of Ussur Brown Katydid, Paratlanticus ussuriensis, occurred in the orchard areas of central Korea during 2006 and 2007. These crickets occur widely in Korea but before 2000 they were not regarded as an agricultural pest and were mainly confined to wooded hillsides. In an attempt to understand this katydid ecology, firstly, we have conducted a life cycle study of the Ussur brown katydid. This katydid spends one or two years as an egg stage. Most of eggs enter the initial diapause, which take place in stage 4. Less than 10% eggs didn't occur the initial diapause and developed until in stage 23 before beginning winter season. In the laboratory experiment, diapause depends on the initial temperature after eggs laid. They had an initial and final diapause around less 25℃. Therefore, it takes two years to hatch at low temperature. On the other hand, eggs are kept at temperatures around over 27℃, entry into the first diapause stage was circumvented and eggs emerged the following spring. That is, the high temperature seems to affect on the life cycle of Katydid. Thus, if they are exposed to high temperature on early egg stage, they emerge next year just after spending a winter.