LYMANTRIA-DISPAR NUCLEOPOLYHEDROVIRUS HRF-1 EXPANDS THE LARVAL HOST-RANGE OF AUTOGRAPHA-CALIFORNICA NUCLEOPOLYHEDROVIRUS

The gypsy moth (Lymantria dispar) is nonpermissive for Autographa cali fornica nucleopolyhedrovirus (AcNPV) infection, We previously isolated a gene, host range factor I (hrf-1), fi om L. dispar nucleopolyhedrov irus that promotes AcNPV replication in Ld652Y cells, a nonpermissive L. dispar cell line (S. M. Thiem, X. Du, M. E. Quentin, and hi. M. Ber ner, J. Virol, 70:2221-2229, 1996), In the present study, we investiga ted the ability of hrf-1 to alter the larval host range of AcNPV. Bioa ssays using recombinant AcNPV bearing hrf-1 were conducted with insect larvae by use of oral infection, AcNPV bearing hrf-1 was infectious f or neonate L. dispar larvae, with a 50% lethal concentration of 1.2 x 10(5) polyhedral inclusion bodies/ml of diet, which is similar to that of wild-type AcNPV for permissive hosts, AcNPV can kill neonate L. di spar larvae at high doses, but it does not kill third-instar larvae, H owever, electron microscopy studies of AcNPV-inoculated third-instar l arvae revealed virus replication in the midgut cells, PCR analyses ind icated that the virus was AcNPV. These results suggest that the block for AcNPV infection of L. dispar larvae is its inability to spread sys tematically from primary infection sites in the midgut epithelium and that this barrier is leaky in neonates, hrf-1 allows AcNPV to overcome this barrier, AcNPV recombinants bearing hrf-1 were also significantl y more infectious for Helicoverpa zea, a resistant species, suggesting that the blocks for AcNPV infection of L. dispar and H. rea larvae ma y be similar.