Per os and intrahemocoelic activity of exocellular and intracellular virus from a wild-type and deleted polyhedrin-gene strain of the nucleopolyhedrovirus of Autographa californica

Repeated attempts to directly compare the activity of the two reported phenotypes (plasma-enveloped, budded virus and polyhedral-derived virus) have been thwarted by the presence of proteinaecous occlusion bodies. The availability of deleted polyhedrin-gene strains of baculoviruses now makes this comparison possible without the use of inactivating, occlusion-body dissolving reagents. Exocellular virus (EXCV), harvested from the supernatant, or intracellular virus (INCV), harvested from intact cells of 24-h and 96-h cultures were used. Both a wild strain (WtAcMNPV) and a deleted polyhedrin-gene strain (PAcMNPV) were used to compare the in vivo activity of the two phenotypes of the nucleopolyhedrovirus of Autographa californica (AcMNPV). The following results were obtained when the EXCV and INCV were administered (per os and by intrahemocoelic injection) to cabbage looper larvae, Trichoplusia ni. When fed to T. ni larvae : (1) EXCV harvested from a 96-h culture of WtAcMNPV was ca. 17-fold more active than EXCV harvested after 24-h of culture ; (2) after 24-h of culture INCV was ca. 167-fold more active than EXCV ; and (3) after 96-h of culture INCV was ca. 29-fold more active than EXCV. There was no difference in activity between EXCV and INCV when T. ni larvae were intrahemocoelically injected.