ON THE SUSCEPTIBILITY OF THE NUN MOTH (LYMANTRIA-MONACHA L) (LEP, LYMANTRIIDAE) TO 2 DIFFERENT VIRUS-STRAINS (NPV) OF THE GYPSY-MOTH (LYMANTRIA-DISPAR L) (LEP, LYMANTRIIDAE)

Cross-infections of L. monacha with two NPV strains of L. dispar, LdNPV and LdNPV kub. resulted in positive reaction is mortality and formation of PIBs for the strain with cube-shaped polyhedral inclusion bodies (LdNPV kub.). The susceptibility of the nun moth was verv low, there was a mortality of 13.0% after infection with a dosage of 10(5) PIBs per larva. The individual larvae of L. monacha produced morphologically different inclusion bodies of cubic or polyhedral shape; in some few cases tetrahedrons were observed. Re-infection-tests with these variants on L. dispar, comparison of the polyhedrins of these types by gel-electrophoresis (SDS-PAGE) and tests of their virulence (LD50, Lt50) showed, that the cubic and polyhedral-shaped forms were just morphological variants of LdNPV kub. having the same pathogenic properties is the inoculum. It was proved, that the tetrahedron-shaped type resulted from the activation of a latent infection of L. monacha with its homologue virus strain (LmNPV) which only came to expression in connection with application of LdNP kub. Infection series showed, that LdNPV kub. had lost its pathogenicity against the nun moth within two passages over this species, probably because of defective virus replication in this host; so there is no genetical adapatation of the virus strain to L. monacha. Changing infection passages over L. monacha and L. dispar reconstituted the infectivity of the virus against the nun moth to its former level.