BackgroundCassava (Manihot esculenta) is the basic source for dietary energy of 500 million people in the world. In Brazil, Erinnyis ello ello (Lepidoptera: Sphingidae) is a major pest of cassava crops and a bottleneck for its production. In the 1980s, a naturally occurring baculovirus was isolated from E. ello larva and successfully applied as a bio-pesticide in the field. Here, we described the structure, the complete genome sequence, and the phylogenetic relationships of the first sphingid-infecting betabaculovirus.ResultsThe baculovirus isolated from the cassava hornworm cadavers is a betabaculovirus designated Erinnyis ello granulovirus (ErelGV). The 102,759 bp long genome has a G + C content of 38.7%. We found 130 putative ORFs coding for polypeptides of at least 50 amino acid residues. Only eight genes were found to be unique. ErelGV is closely related to ChocGV and PiraGV isolates. We did not find typical homologous regions and cathepsin and chitinase homologous genes are lacked. The presence of he65 and p43 homologous genes suggests horizontal gene transfer from Alphabaculovirus. Moreover, we found a nucleotide metabolism-related gene and two genes that could be acquired probably from Densovirus.ConclusionsThe ErelGV represents a new virus species from the genus Betabaculovirus and is the closest relative of ChocGV. It contains a dUTPase-like, a he65-like, p43-like genes, which are also found in several other alpha- and betabaculovirus genomes, and two Densovirus-related genes. Importantly, recombination events between insect viruses from unrelated families and genera might drive baculovirus genomic evolution.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-856) contains supplementary material, which is available to authorized users.

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BackgroundErinnyis ello granulovirus (ErelGV) is a betabaculovirus infecting caterpillars of the sphingid moth E. ello ello (cassava hornworm), an important pest of cassava crops (Manihot esculenta). In this study, the genome of seven field isolates of the virus ErelGV were deep sequenced and their inter- and intrapopulational sequence diversity were analyzed.ResultsNo events of gene gain/loss or translocations were observed, and indels were mainly found within highly repetitive regions (direct repeats, drs). A naturally occurring isolate from Northern Brazil (Acre State, an Amazonian region) has shown to be the most diverse population, with a unique pattern of polymorphisms. Overall, non-synonymous substitutions were found all over the seven genomes, with no specific gathering of mutations on hotspot regions. Independently of their sizes, some ORFs have shown higher levels of non-synonymous changes than others. Non-core genes of known functions and structural genes were among the most diverse ones; and as expected, core genes were the least variable genes. We observed remarkable differences on diversity of paralogous genes, as in multiple copies of p10, fgf, and pep. Another important contrast on sequence diversity was found on genes encoding complex subunits and/or involved in the same biological processes, as late expression factors (lefs) and per os infectivity factors (pifs). Interestingly, several polymorphisms in coding regions lie on sequences encoding specific protein domains.ConclusionsBy comparing and integrating information about inter- and intrapopulational diversity of viral isolates, we provide a detailed description on how evolution operates on field isolates of a betabaculovirus. Our results revealed that 35–41% of the SNPs of ErelGV lead to amino acid changes (non-synonymous substitutions). Some genes, especially non-core genes of unknown functions, tend to accumulate more mutations, while core genes evolve slowly and are more conserved. Additional studies would be necessary to understand the actual effects of such gene variations on viral infection and fitness.Electronic supplementary materialThe online version of this article (10.1186/s12864-018-5070-6) contains supplementary material, which is available to authorized users.

The method of single-strand conformational polymorphism (SSCP) was modified in our laboratories for the characterization of baculoviruses, insect viruses with great potential for use as bioinsecticides in biological protection programs. A series of primers were synthesized after the comparison of the polyhedrin gene sequences of over 20 baculoviruses. Polyhedrin is a highly conserved protein which is responsible for the persistence of the virus in the environment. Universal primers were designed which could be used in polymerase chain reactions (PCR) containing genomic DNA from an array of nucleopolyhedrosis viruses (NPVs) including these which are used as biopesticides against important pests of forests and crops, such as Anticarsia gemmatalis, Spodoptera frugiperda, Lymantria dispar, Lymantria monacha and many others. PCR products were denatured and subjected to single-strand DNA electrophoresis at variable temperatures (MSSCP) where, after silver staining, they gave ssDNA band patterns characteristic for each baculovirus species. This technique can be potentially applied to detect baculoviruses in insects collected in the field, as well as to plant tissues and the excrements or bodies of predators without need for sequencing the PCR products. Sometimes MSSCP can be used not only for species determination but also as an indication of genomic variability which can be related to infectivity.

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