Comparison of Field-Collected Ascovirus Isolates by DNA Hybridization, Host Range, and Histopathology

Abstract

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 fromSpodoptera frugiperda,and the other four were fromAutographa precationis, Heliothis virescens, Helicoverpa zea,andTrichoplusia ni.DNA–DNA hybridization studies showed that the six isolates belonged to three distinct viral species, with the isolates fromS. frugiperdacomposing one species, those fromA. precationisandH. virescensa second species, and those fromH. zeaandT. nia 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,andFeltia subterranea.Though some variation existed between the different isolates of each viral species, distinct patterns were apparent for each. The viral species fromS. frugiperdahad a host range that was limited primarily toSpodopteraspecies and both isolates of this virus only replicated and caused significant pathology in the fat body, whereas the viral species fromA. precationisandH. virescenshad 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 fromT. niandH. zeareadily 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.