Relative activity of baculoviruses of the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae)

The relative activities of the granulovirus (PxGV) and the nucleopolyhedrovirus (PxMNPV) of the diamondback moth, Plutella xylostella (L.), against this insect were evaluated in the laboratory. Similar numbers of occlusion bodies (OBs) of PxGV and PxMNPV were required to kill P. xylostella. However, cadavers of insects infected with PxGV contained more OBs per unit weight than did cadavers infected with PxMNPV. Less cadaver material was thus required to kill insects with PxGV. Larvae that were killed by PxGV survived approximately 2 d longer than did those killed by PxMNPV. When P. xylostella larvae were fed both viruses together, mortality was higher than that caused by either virus alone. The virulence of PxMNPV produced in P.␣xylostella did not differ from that of PxMNPV produced in the beet armyworm, Spodoptera exigua (Hübner). S. exigua was less susceptible to PxMNPV than to its homologous nucleopolyhedrovirus, SeMNPV.