Pathogenicity and Production of Mamestra brassicae Nucleopolyhedrovirus (MabrNPV)-K1

The objective of our study was the evaluation of pathogenicity of a local strain of Mamestra brassicae nucleopolyhedrovirus-K1 (MabrNPV-K1) derived from a diseased larva of M. brassicae found in Korea. The effect of temperature and larval instar on the pathogenicity and production of MabrNPV-K1 was determined under laboratory conditions. The median lethal concentration (LC∧50) values of MabrNPV-K1 for 3rd instar larvae were 3.7×10⁴ PIBs/larva at 20℃, 9.9×10² PIBs/larva at 25℃ and 3.8×10² PIBs/larva at 30℃, respectively. The LC∧50 for the 4th instar larvae was similar to that for the 3rd instar larvae. However, the pathogenicity to the 3rd instar larvae was higher than that to the 4th instar larvae. The median lethal time (LT∧50) values of MabrNPV-K1 were 11.4 to 5.0 days at 30℃ and 18.3 to 5.5 days at 25℃ for the 3rd instar larvae. The LT∧50 value was lowered as temperature went up to 30℃ and dependent on viral concentration. In production efficiency of MabrNPV-K1 using M. brassicae larvae, the mortality of the 3rd instar larvae was 100% when inoculated with 1.0×10∨5 PIBs/larva and the yield of MabrNPV-K1 was maximal. Regarding the mortality, yield of polyhedra, inoculation doses and required time, the 1.0×10⁴ PIBs/larva at 30℃ was determined as optimal conditions producing polyhedra efficiently.