COMPARISON OF FIELD-COLLECTED ASCOVIRUS ISOLATES BY DNA HYBRIDIZATION, HOST-RANGE, AND HISTOPATHOLOGY

Six field-collected ascovirus isolates obtained from five noctuid spec ies 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 fro m Autographa precationis, Heliothis virescens, Helicoverpa zea, and Tr ichoplusia ni. DNA-DNA hybridization studies showed that the six isola tes belonged to three distinct viral species, with the isolates from S . frugiperda composing one species, those from A. precationis and H. v irescens a second species, and those from H. tea and T. ni a third spe cies. The host range and histopathology of each isolate was studied in eight noctuid species, S. frugiperda, Spodoptera ornithogalli, Spodop tera exigua, Spodoptera eridania, H. virescens, H. tea, A. precationis , and Feltia subterranea. Though some variation existed between the di fferent isolates of each viral species, distinct patterns were apparen t 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 bod y, whereas the viral species from A. precationis and H. virescens had a much broader host range that included most of the species tested, bu t also had a tissue tropism primarily restricted to the fat body. The viral species from T. ni and H. tea readily infected all the hosts tes ted, where the principal site of replication and significant pathology was the epidermis. In many test hosts, however, this viral species al so replicated and caused significant pathology in the tracheal epithel ium and to a lesser extent in the fat body. Aside from contributing to knowledge of ascovirus biology, these studies indicate that DNA hybri dization profiles combined with studies of host range and tissue tropi sm can be used as characters for defining ascovirus species. (C) 1998 Academic Press.