Control of Pieris rapae by granulosis viruses

Abstract

Laboratory tests with two strains of granulosis virus—one from New Zealand and the other from England—showed that 100% control of Pieris rapae L. larvae was achieved in 9 and 11 days respectively. Results of sampling in 61 different areas in home gardens or on farms showed that deaths of caterpillars due to virus were not common up to the end of January, but that by the end of the first week in February the mortality rose to nearly 20% of white-butterfly larvae; then to approximately 57% by 21 February; to 75% during the last week in February, 77% in March, and then fell slightly to 70% during April. During the latter two months and late February, however, there were nine cases where complete control of larvae was recorded, and a further ten cases where control percentages were very high.