Submitted to: Japanese Journal of Applied Entmology and Zoology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 10, 1999
Publication Date: N/A
Interpretive Summary: Natural, viral diseases of insects are being developed and formulated into safe, effective biological control products. These viruses of insects generally produce two different forms. One form is readily available while the second form is generally unavailable because of how it is "packaged." Genetically removing the "packaging" may increase its availability and its ability to rapidly kill the pest insect and thereby increase its potential for use as a biological control product. Therefore, it was important to know whether the two different forms (i.e., the natural form and the form in which the package was genetically removed) had different levels of kill against a common insect pest of cabbage and cole crops. We demonstrated that the two viral forms had different levels of kill dependent upon when they were produced. Viral forms produced early inside the cells had more kill than those found outside the cells. Our results provided additional information on the activity of viral preparations, and how viruses may control insect pests, which may impact scientists and producers interested in producing insect viral products.
Technical Abstract: 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. Extracellular virus (ECV), harvested from the supernatant, or intracellular virus (ICV), harvested from intact cells, of 24-h and 96-h cultures were used. Both a wild strain (WtAcMNPV) and a polyhedrin-gene deleted strain (P-AcMNPV) 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 ECV and ICV were administered (per os and by intrahemocoelic injection) to the cabbage looper larvae, Trichoplusia ni. When fed to T. ni larvae: (1) ECV Vharvested from a 96-h culture of WtAcMNPV was ca. 17-fold more active than ECV harvested after 24-h; (2) after 24-h of culture ICV was ca. 167-fold more active than ECV; and (3) after 96-h of culture ICV was ca. 29-fold more active than ECV. There was no difference in activity between ECV and ICV when T. ni larvae were injected intrahemocoelically.