A comparison of the adaptations of strains of Lymantria dispar multiple nucleopolyhedrovirus to hosts from spatially isolated populations.

The adaptation of pathogens to either their hosts or to environmental conditions is the focus of many current ecological studies. In this work we compared the ability of six spatially-distant Lymantria dispar (gypsy moth) multiple nucleopolyhedrovirus (LdMNPV) strains (three from eastern North America and three from central Asia) to induce acute infection in gypsy moth larvae. We also sequenced the complete genome of one Asian (LdMNPV-27/0) and one North American (LdMNPV-45/0) strain which were used for bioassay. We found that all of the North American virus strains, with the exception of one, demonstrated higher potency than the Asian virus strains, either in North American (Lymantria dispar) larvae or, in Asian (Lymantria dispar asiatica) larvae. Complete genome sequencing revealed two gene deletions in the LdMNPV-27/0 strain: the virus enhancin factor gene (vef-1) and the baculovirus repeated orf gene (bro-p). These deletions were not seen in the LdMNPV-45/0 strain nor in other American strains available in archiving systems. We also found deletions of the bro-e and bro-o genes in LdMNPV-45/0 strain but not in the LdMNPV-27/0 strain. The phylogenetic inference with an alignment of the 37 core gene nucleotide sequences revealed the close relationship of the LdMNPV-45/0 strain with other American strains accessed in GenBank (Ab-a624 and 5-6) while the LdMNPV-27/0 strain was clustered together with the LdMNPV-3054 strain (isolated in Spain) instead of predicted clustering with LdMNPV- 3029 (isolated in Asia). Our study demonstrated that first, different LdMNPV isolates from the same metapopulations of L. dispar exhibit little or no difference in the degree of virulence towards host larvae and second, that locality of host population is not an important driver of LdMNPV virulence. Virulence of LdMNPV is determined only by viral genetics. The genetic differences between North American and Central Asian virus strains are discussed.

[THE PROOF OF VERTICAL TRANSMISSION OF THE NUCLEOPOLYHEDROVIRUS IN MANY GENERATIONS OF THE GYPSY MOTH LYMANTRIA DISPAR L].

INTRODUCTION: Insect viruses can play an important role in population dynamics of their hosts. That is why the problem of permanent viral infection support among virus-positive insects is associated with one of the intriguing problems of general biology and virology. MATERIALS AND METHODS: Under laboratory conditions, the modeling of the vertical transmission of the nucleopolyhedrovirus (NPV) gypsy moth was implemented at relatively high level of mortality among insects of parental generation (60%). The diagnostics of the occult virus was executed by the PCR method among insects before their infection under laboratory conditions, as well as among insects that survived after inoculation. RESULTS: The NPV-caused mortality among insects that survived after infection in generations F1, F2, and F3 was 14 ± 4%, 10 ± 4%, and 5 ± 0.5%, respectively. In the following three generations NPV-induced mortality was not noticed. DISCUSSION: The level of the virus-positive individuals among the gypsy moth embryos in all occasions was higher than the NPV-induced mortality of insects. Thus, the given results show that the presence of virus among insect does not mean inevitable mortality of their hosts. Perhaps, the viral DNA can completely or partly lose its infectivity but may exist in the analyzed insect samples. CONCLUSIONS: The viral infection can be formed among progeny surviving after inoculation of insects. It can be actuated during three generations of the gypsy moth. The level of the virus-positive individuals among the gypsy moth embryos determined by the PCR method in daughter generations was higher than the NPV- induced mortality of insects.