Comparison of in vivo activity of virus from a deleted polyhedrin-gene strain of a single-nucleocapsid baculovirus and a multiple-nucleocapsid baculovirus

Abstract

Larvae of Trichoplusia ni, Helicoverpa zea and Heliothis virescens were assayed for their relative suscepti-bility to in vitro produced, nonoccluded virus (P-NOV) from a deleted polyhedrin-gene strain of the nucleopolyhedroviruses of Autographa californica (P-AcMNPV) and Helicoverpa zea (P-HzSNPV). There was a 90-fold difference in P- NOV activity (LC50 values based upon TCID50/mm2) between P-AcMNPV (vs. T. ni) and P-HzSNPV (vs. H. zea) when each virus was assayed against its respective permissive host. These differences in P-NOV activity were within the same range one would expect based upon their reported LC50 values and the estimated numbers of virions embedded in occlusion bodies (OB) of the wild-type (Wt) isolate of these viruses. Differences in LC50 values (TCID50/mm2) between P-NOV of P-AcMNPV and P-NOV of P-HzSNPV using H. virescens larvae (a permissive host susceptible to both viruses) however, were much greater ( > 300-fold) than expected if based upon the number of virions/WtOB. Closer agreements in LC50 values between P-NOV and occluded viruses of WtOB were obtained for H. zea or H. virescens larvae exposed to P-HzSNPV (ca. 1.3-fold difference) or H, zea and H. virescens larvae exposed to P-AcMNPV (ca. a 15-fold difference). Results using a non-susceptible host (P-NOV of P-HzSNPV vs. T. ni) or a semi-permissive host (P-NOV of P-AcMNPV vs. H, zea) generally agreed with previous citations using occluded virions of WtOB.