The genome sequence and evolution of baculoviruses.

Comparative analysis of the complete genome sequences of 13 baculoviruses revealed a core set of 30 genes, 20 of which have known functions. Phylogenetic analyses of these 30 genes yielded a tree with 4 major groups: the genus Granulovirus (GVs), the group I and II lepidopteran nucleopolyhedroviruses (NPVs), and the dipteran NPV, CuniNPV. These major divisions within the family Baculoviridae were also supported by phylogenies based on gene content and gene order. Gene content mapping has revealed the patterns of gene acquisitions and losses that have taken place during baculovirus evolution, and it has highlighted the fluid nature of baculovirus genomes. The identification of shared protein phylogenetic profiles provided evidence for two putative DNA repair systems and for viral proteins specific for infection of lymantrid hosts. Examination of gene order conservation revealed a core gene cluster of four genes, helicase, lef-5, ac96, and 38K(ac98), whose relative positions are conserved in all baculovirus genomes.

Host Stage Structure and Baculovirus Transmission in Mamestra brassicae L. (Lepidoptera: Noctuidae) Larvae: a Laboratory Examination of Small Scale Epizootics / Estrutura Etária do Hospedeiro e Transmissão de Baculovírus em Larvas de Mamestra brassicae L. (Lepidoptera: Noctuidae): Uma Análise de Epizootias em Pequena Escala em Laboratório

Os efeitos da estrutura etária e da densidade do hospedeiro na transmissão horizontal de um baculovírus foram investigados em laboratório, utilizando-se populações de lagarta do repolho, Mamestra brassicae L. (Lepidoptera: Noctuidae). Os insetos foram mantidos a três combinações de ínstares e três densidades populacionais em recipientes fechados contendo larvas infectadas. As larvas foram observadas diariamente e o número de mortes e o tempo letal foram registrados. Os níveis de mortalidade viral foram marginalmente superiores em recipientes contendo hospedeiros sob maior densidade populacional. As larvas apresentaram um risco de infecção aparentemente maior quando combinações de instares mais avançados foram usadas. Os níveis de mortalidade de larvas mais velhas foram maiores que as de larvas mais jovens. As médias de tempo letal das populaç ões larvais foram maiores para larvas mais jovens, observando-se um declínio mais acentuado na curva de sobrevivência das larvas em estágio mais adiantado de desenvolvimento.

The effects of stage structure and host density on baculovirus horizontal transmission were examined in the laboratory using larvae of the cabbage moth, Mamestra brassicae L. (Lepidoptera: Noctuidae). Insects were reared at three instar combinations and three host densities in closed containers with infected larvae. Insects were observed daily and the number of deaths and time to death were recorded. Levels of virus mortality were marginally higher in the containers where a higher density of hosts was introduced. Larvae appeared to have a greater risk of infection when late instar combinations were used. Final levels of mortality of older larvae were significantly higher than those of younger larvae. Mean times to death of larval populations were longer for larvae at earlier instar combinations, with a faster decrease in survivorship of older larvae over time.

Whole genome analysis of the Epiphyas postvittana nucleopolyhedrovirus.

The nucleotide sequence of the Epiphyas postvittana nucleopolyhedrovirus (EppoMNPV) genome has been determined and analysed. The circular dsDNA genome contains 118584 bp, making it the smallest group I NPV sequenced to date. The genome has a G+C content of 40.7% and encodes 136 predicted open reading frames (ORFs), five homologous repeat regions and one unique repeat region. Of the genome, 92.9% encodes predicted ORFs and 2.2% is in repeat regions; the remaining 4.9% of the genome comprises nonrepeat intergenic regions. EppoMNPV encodes homologues of 126 Orgyia pseudotsugata MNPV (OpMNPV) ORFs and 120 Autographa californica MNPV ORFs, with average identities of 64.7 and 53.5%, respectively. Between the four sequenced group I NPVs, 117 ORFs are conserved, whereas 86 ORFs are conserved between all fully sequenced NPVs. A total of 62 ORFs is present in all baculoviruses sequenced to date, with EppoMNPV lacking a homologue of the superoxide dismutase (sod) gene, which has been found in all other fully sequenced baculoviruses. Whole genome phylogenetic analyses of the ten fully sequenced baculoviruses using the sequences of the 62 shared genes, gene content and gene order data sets confirmed that EppoMNPV clusters tightly with OpMNPV in the group I NPVs. The main variation between EppoMNPV and OpMNPV occurs where extra clusters of genes are present in OpMNPV, with sod occurring in one such cluster. EppoMNPV encodes one truncated baculovirus repeated ORF (bro) gene. The only repeated ORFs are the four iap genes. Eight, randomly distributed, unique ORFs were identified on EppoMNPV, none of which show any significant homology to genes in GenBank.