In general, trees showing water stress planted in a harsh environment like urban landscapes are weakened and can be easily infested by insect borers, such as cerambycid and curculionid beetles. Prunus × yedoensis constitutes a significant portion of urban street trees in Korea and there has been an increasing incidence of damage caused by red-necked longhorned beetle (RLB), Aromia bungii. When water stress is incresed, the production of resin, a natural defense mechanism against the infestation of Aromia bungii larvae, can be decreased that impact on larval survival rates. This study was conducted to investigate the relationship between infestation rate of RLB and water stress of cherry trees. We counted number of larval entrance and adult emergence holes in 50 trees and monitored adult’s behaviors during daytime. In addition, we measured water stress using a pressure chamber for each tree.