Control of the Common Cabbage Worm, Piers rapae crucivora BOISDUVAL by a Granulosis Virus

Abstract

A granulosis virus from Hawaii caused a highly virulent disease in Pieris rapae crucivora BOISDUVAL. When the eggs of P. rapae crucivora were laid on cabbage plants which had been contaminated with a granulosis virus, more than 51% of hatched larvae were killed by the virus in 6 to 8 days during their second- or early third-instar stage. From this it appears that they had become infected in first or early second instar stage. When the virus suspension obtained by macerating 80 diseased larvae was sprayed on 10a cabbage field, 78.3% of the fourth- and fifth-instar larvae were killed in 6 days and 79.5% in 12 days. Furthermore, the number of living larvae and pupae per 50 cabbage plants were very greatly reduced within 12 days. The leaf damage index in the virus treated plots was 39.0% as compared to 74.5% in the non-treated plots. If the virus was combined with Depterex or Endrin, the control was found to be more effective.