The two AcNPV strains against the second instar larva of S. exiguaare compared by means of bioassay. Analysis on virulence and insect-killing rate ofthe two AcNPV strains show that in terms of virulence, LD(50) of AcNPV-A is 131.8 PIB/ILarva, LD(50) of AcNPV-B is 1696. 8 PIB/Larva,that is to say, AcNPV-Apropagated from S. exigua is 10 times as high as AcNPV-B propagated fromspodoptera frugiperda (sf9) cell in virulence; while in terms of insect-killing rate,LT(50), of AcNPV-A is 4. 46 days, LT(50) of AcNPV-...