Submitted to: Journal of Applied Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/16/1998
Publication Date: N/A
Citation: Interpretive Summary: Viruses that only attack insects are environmentally safe biological control agents that can be used to control harmful insect pests of field and vegetable crops. The active agent of these viruses are normally encapsulated into a small soccer-like body called an occlusion body. The problem is that these occlusion bodies make it impossible to directly compare the activity of different strains or possibly to look for more active, faster acting strains of viruses. We demonstrated that strains, genetically modified to eliminate the occlusion body, makes it possible to characterize the activity of strains attacking three major insect pests of vegetable and field crops. Industrial, academic, or governmental scientists could use these modified strains and procedures to directly compare the activity of different strains of insect viruses.
Technical Abstract: Larvae of Trichoplusia ni, Helicoverpa zea and Heliothis virescens were assayed for their relative susceptibility to in vitro produced, nonoccluded virions (P-NOV) from a deleted polyhedrin-gene strain of the nucleopolyhedrosis of Autographa californica (P-AcMNPV) and Helicoverpa zea (P-HzSNPV). There was ca. a 123-fold difference in P-NOV infectivity between P-PcMNPV (vs. T. ni) and P-HzSNPV (vs. H. zea) when each strain wa assayed against its respective homologous host. These differences in P-NOV infectivity were of the same magnitude one would anticipate if based upon the reported LC-50 values for PIB-occluded virions of the wild-type (Wt). Infectivity differences between P-NOV of P-AcMNPV and P-NOV of P-HzSNPV using H. virescens larvae (a host susceptible to both isolates) however, were much greater (> 100-fold) than would be anticipated if based upon reported LC-50 values for WtPIB-occluded virions. Closer agreements in LC- -50 values between P-NOV and WtPIB-occluded virions were obtained for H. ze or H. virescens larvae, exposed to P-HzSNPV or P-AcMNPV. Nonhomologous host comparisons (P-NOV of P-HzSNPV vs. T. ni, or P-NOV of P-AcMNPV vs. H. zea) generally agreed with previous reports using WtPIB-occluded virions.