Rate of response to selection forNephotettix virescens(Distant) virulence was studied for 20 generations on five rice cultivars with different levels of resistance. Rate of response to selection on all cultivars varied depending on the measurement criteria. Survival, growth, progeny production, and weight increased, and developmental period decreased, with selection time. Based on survival, theN. virescenspopulation became highly virulent within one to four generations, whereas high virulence as measured by progeny production generally required more generations of selection. Virulence as measured by the ability to vector tungro virus also increased with selection time.