Growth of nuclear polyhedrosis virus in larvae of the cabbage moth, Mamestra brassicae L

Growth of nuclear polyhedrosis virus (NPV) in 5 larval instars of cabbage moth, Mamestra brassicae, has been quantified using 2 methods. Numbers of polyhedra were estimated by light microscope counts while concentrations of virus protein antigen were estimated using ELISA. Virus growth was rapid initially but slowed during its later stages, although ELISA protein concentrations decreased once a peak had been reached. There was a linear correlation between polyhedral counts and virus protein during the initial growth phase. Maximum polyhedral production ranged from 2 x 107 (first instar) to 3.4 x 109 (fifth instar) and could be correlated directly to increasing larval weight. Using ELisa, virus antigen was detectable at least 24 hours before polyhedra were observed under the light microscope. Productivity ratios ranged from 83,500 in the first instar to 1352 in the fifth instar.