An infectivity test of Syngrapha falcifera multiple nuclear polyhedrosis virus (SfaMNPV) against Plutella xyiostella (Px.), Helilcoverpa armigera (Ha.) and Laphygma exigua (Le.) was carried out in our laboratory. By bioassay on second instar Px., Ha. and Le. larvae, the LC 50 of SfaMNPV was determined as 2.47×10 6, 7.96×10 5 and 2.22×10 5PIB/ml respectively. When they were infected at a concentration of 4.22×10 7PIB/ml and 4.22×10 6PIB/ml, the LT 50 was 6.15d and 7.32d, 8.20d and 11...