Sunlight persistence and rainfastness of spray-dried formulations of baculovirus isolated from Anagrapha falcifera (Lepidoptera: Noctuidae).

Nuclear polyhedrosis viruses such as the one isolated from the celery looper, Anagrapha falcifera (Kirby) (AfMNPV), have the potential to be successful bioinsecticides if improved formulations can prevent rapid loss of insecticidal activity from environmental conditions such as sunlight and rainfall. We tested 16 spray-dried formulations of AfMNPV to determine the effect of different ingredients (e.g., lignin, corn flour, and so on) on insecticidal activity after simulated rain and simulated sunlight (at Peoria, IL) and natural sunlight exposures (at Tifton, GA). The most effective formulation contained pregelatinized corn flour and potassium lignate, which retained more than half of its original activity after 5 cm of simulated rain, and almost full activity after 8 h of simulated sunlight. In Georgia, formulations made with and without lignin were compared for persistence of insecticidal activity when exposed to natural sunlight. In addition, the effect of fluorescent brighteners as formulation components and spray tank additives was tested. Results showed that the formulations with lignin had more insecticidal activity remaining after sunlight exposure than formulations without lignin. The inclusion of brighteners in the formulation did not improve initial activity or virus persistence. However, a 1% tank mix significantly enhanced activity and improved persistence. Scanning electron micrographs revealed discreet particles, and transmission electron micrographs showed virus embedded within microgranules. Results demonstrated that formulations made with natural ingredients could improve persistence of virus-based biopesticides.

Comparison of field-collected ascovirus isolates by DNA hybridization, host range, and histopathology.

Six field-collected ascovirus isolates obtained from five noctuid species in the continental United States were compared with respect to the general relatedness of their DNA, host range, and histopathology. Two isolates were from Spodoptera frugiperda, and the other four were from Autographa precationis, Heliothis virescens, Helicoverpa zea, and Trichoplusia ni. DNA-DNA hybridization studies showed that the six isolates belonged to three distinct viral species, with the isolates from S. frugiperda composing one species, those from A. precationis and H. virescens a second species, and those from H. zea and T. ni a third species. The host range and histopathology of each isolate was studied in eight noctuid species, S. frugiperda, Spodoptera ornithogalli, Spodoptera exigua, Spodoptera eridania, H. virescens, H. zea, A. precationis, and Feltia subterranea. Though some variation existed between the different isolates of each viral species, distinct patterns were apparent for each. The viral species from S. frugiperda had a host range that was limited primarily to Spodoptera species and both isolates of this virus only replicated and caused significant pathology in the fat body, whereas the viral species from A. precationis and H. virescens had a much broader host range that included most of the species tested, but also had a tissue tropism primarily restricted to the fat body. The viral species from T. ni and H. zea readily infected all the hosts tested, where the principal site of replication and significant pathology was the epidermis. In many test hosts, however, this viral species also replicated and caused significant pathology in the tracheal epithelium and to a lesser extent in the fat body. Aside from contributing to knowledge of ascovirus biology, these studies indicate that DNA hybridization profiles combined with studies of host range and tissue tropism can be used as characters for defining ascovirus species.

Comparative study of virion structure, protein composition and genomic DNA of three ascovirus isolates.

The virions of three ascoviruses isolated from the noctuids Heliothis zea, Spodoptera frugiperda and Trichoplusia ni were compared with respect to their size and structure, protein composition and the size and relatedness of their DNAs. The virions of the isolates from H. zea (HAV) and T. ni (TAV) were allantoid in shape (400 x 130 nm), enveloped and contained an inner particle which appeared to have an internal lipid bilayer surrounding the DNA core. The virions of the S. frugiperda isolate (SAV) were similar in structure and size, but were bacilliform in shape, and after formation, were often occluded in vesiculate occlusion bodies. In preparations of purified virions of each isolate, at least 12 polypeptides were detected that ranged in size from 10K to 200K and contained a major species of about 50K. The genome of SAV was about 140 kbp in size, whereas those of TAV and HAV were approximately 180 kbp. Analysis of DNA fragment patterns of the three isolates generated with BamHI, HindIII or XhoI, as well as DNA-DNA dot blot and Southern blot hybridization studies, demonstrated that HAV and TAV were closely related but not identical. The DNA from SAV, however, did not hybridize with the DNA from either of the other isolates. Thus the ascovirus isolates from T. ni and H. zea are considered variants of the same virus, whereas the isolate from S. frugiperda is a separate member of the ascovirus group.

Analysis of the Spodoptera frugiperda Nuclear Polyhedrosis Virus Genome by Restriction Endonucleases and Electron Microscopy.

Restriction endonuclease analysis was used to differentiate between four strains of Spodoptera frugiperda nuclear polyhedrosis virus from different geographical areas. In addition, partial denaturation was performed, and a partial denaturation map was constructed for the Ohio strain of this virus.

Spodoptera frugiperda Nuclear Polyhedrosis Virus Genome: Physical Maps for Restriction Endonucleases BamHI and HindIII.

The physical map for the genome of Spodoptera frugiperda nuclear polyhedrosis virus was constructed for restriction endonucleases BamHI and HindIII. The ordering of the restriction fragments was accomplished by cross-blot hybridization of BamHI, HindIII, and EcoRI fragments. The alignment of the HindIII fragments within the BamHI map was achieved by double digestion with the two restriction endonucleases followed by cross-blot hybridization. The results showed that the viral genome consisted of mainly unique sequences. In addition, the circular nature of the viral genome was reaffirmed.