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SUMMARYThe restriction endonucleases, BamHI, EcoRl, HindlII and PstI, cleave Oryctes baculovirus (strain PV505) DNA into 21, 43, 23 and seven fragments respectively. A large number of these fragments were cloned into the bacterial plasmids pUC8 and pBR328. These clones encompass 96 % of the genome. The restriction sites for the four endonucleases were mapped using double and partial digestions of cloned fragments as well as hybridization of labelled fragments to Southern transfers of cleaved DNA.When HindlII fragment D and BamHI fragment D were hybridized to Southern transfers six regions containing reiterated sequences were found. The physical map for Oryctes baculovirus could not be orientated with respect to other published baculovirus maps because the BamHI fragment F of Autographa californiea nuclear polyhedrosis virus which contains conserved polyhedrin gene sequences common to occluded baculoviruses did not bind to Oryctes baculovirus DNA.

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Establishment of a persistent infection of Spodoptera frugiperda nuclear polyhedrosis virus (NPV) in Spodoptera frugiperda (S.f.) cells occurred in three phases: the first phase was characterised by high levels of cell infection and death, the second phase by decreasing cell infection levels leading to the final phase where less than one per cent of the cells were infected during any subculture. The virus persisted at this level of infection provided the cells were maintained by regular subculturing and incubated at the optimum growth temperature of 27 degrees C. Because of the low proportion of cells infected, cultures of virus-free cells could be selected ('cured') by dilution of the persistent infection without the use of viral antiserum. Unlike the parent S.f. cells, cultures of cured cells were partially resistant to infection with S. frugiperda NPV or infection with an unrelated baculovirus Autographa californica NPV. A. californica NPV, which is cytolytic for the parent S.f. cell line, established a persistent infection in the cured cells. The establishment pattern was similar to that previously found for S. frugiperda NPV and only one to five per cent of the cells were infected at equilibrium. Cured cells from the A. californica NPV persistent infection were highly resistant to infection with both S. frugiperda NPV and A. californica NPV. All attempts to find a viral interference phenomenon to explain the resistance of the cured cells were unsuccessful. All cell types adsorbed virus equally well. Slower growth of S.f. cells cured from the persistent A. californica NPV infection is the only difference so far observed between any of the S.f. cell types.

Two nodaviruses, both isolated from New Zealand scarab beetles, replicated in DSIR-HA-I 179 (HA) cells derived from the black beetle, Heteronychus arator (Coleoptera: Scarabaeidae). Black beetle virus and Flock House virus, isolated from the grass grub (Costelytra zealandica) produced a characteristic cytopathic effect in cells.