The fall armyworm,Spodoptera frugiperda,which destroys many economic crops such as rice and maize,has recently invaded China.Insect viruses as biological control agents play important roles in killing pests.One potential viral insecticide is the environmentally highly infective and virulent densovirus.We successfully rescued Junonia coenia densovirus (JcDV) using its infectious clone in different insect cell lines and larvae of three insect species.Results showed that the lysate of cultured insect cells transfected by the JcDV infectious clone killed the 2nd instar S.frugiperda.The LD50 of homogenate from JcDV-infected Spodoptera litura to the 2nd instar S.frugiperda (1.76×108 viral genome copies per larva during 10 d post infection) was higher than that of the 2nd instar S.litura (7.39×107 JcDV genome copies) or Helicoverpa armigera larvae (9.71×107 JcDV genome copies).The LT50 of the S.litura homogenate (2.60×109 viral genome copies each larva) to the 2nd instar S.frugiperda was 6.96 d,longer than that of the S.litura (6.18 d) or the 2nd instar H.armigera (5.94 d).JcDV could infect the fat body of H.armigera,but not S.frugiperda or S.litura.Although JcDV can infect all three lepidopteran species,their susceptibility to the virus differs.JcDV has great potential as a biological control agent against pests such as S.frugiperda.