Bracovirus is a genus of viruses, in the family Polydnaviridae. Bracoviruses are an ancient symbiotic virus contained in parasitic braconid wasps that evolved off of the nudivirus about 190 million years ago and has been evolving at least 100 million years.[1] It is one of two genera belonging to the Polydnaviridae family, Ichnovirus being the other genus. There are 32 species in this genus.[2] [3]
Parasitoid wasps in the subfamilies Microgastrinae, Miracinae, Cheloninae, Cardiochilinae, Khoikhoiinae, and Mendesellinae are the natural hosts for Bracoviruses, though the virus does not cause disease in these wasps. Instead, the wasps are themselves parasites of lepidoptera. The wasp injects one or more eggs into its lepidoptera host along with a quantity of virus. The virus does not replicate inside the wasp's host, but expression of viral genes prevents its immune system from killing the wasp's egg and causes other physiological alterations that ultimately cause the parasitized host to die. Studies conducted on Cotesia congregata have shown that male wasps do contain proviral sequences of DNA, but the females are the ones responsible for the amplification of the viral DNA.[4]
The genus Bracovirus contained the 32 species in ICTV versions 1999a-2020[5] The genus Bracoviriform contains the following 31 species starting ICTV version 2021[3] The species Ichnoviriform rostralis, previously known as Tranosema rostrale bracovirus was moved to Ichnoviriform (Ichnovirus) from Bracoviriform (Bracovirus) in 2021.
| Species | Previous name, Virus name | Abbreviation | |
|---|---|---|---|
| Bracoviriform altitudinis | Chelonus altitudinis bracovirus | CalBV | |
| Bracoviriform argentifrontis | Ascogaster argentifrons bracovirus | AaBV | |
| Bracoviriform blackburni | Chelonus blackburni bracovirus | CbBV | |
| Bracoviriform canadense | Hypomicrogaster canadensis bracovirus | HcBV | |
| Bracoviriform congregatae | Cotesia congregata bracovirus | CcBV | |
| Bracoviriform crassicornis | Apanteles crassicornis bracovirus | AcBV | |
| Bracoviriform croceipedis | Microplitis croceipes bracovirus | McBV | |
| Bracoviriform curvimaculati | Chelonus nr. curvimaculatus bracovirus | CcBV | |
| Bracoviriform demolitoris | Microplitis demolitor bracovirus | MdBV | |
| Bracoviriform ectdytolophae | Hypomicrogaster ectdytolophae bracovirus | HcEV | |
| Bracoviriform facetosae | Diolcogaster facetosa bracovirus | DfBV | |
| Bracoviriform flavicoxis | Glyptapanteles flavicoxis bracovirus | GflBV | |
| Bracoviriform flavipedis | Cotesia flavipes bracovirus | CfBV | |
| Bracoviriform flavitestaceae | Phanerotoma flavitestacea bracovirus | PfBV | |
| Bracoviriform fumiferanae | Apanteles fumiferanae bracovirus | AfBV | |
| Bracoviriform glomeratae | Cotesia glomerata bracovirus | CgBV | |
| Bracoviriform hyphantriae | Cotesia hyphantriae bracovirus | ChBV | |
| Bracoviriform inaniti | Chelonus inanitus bracovirus | CinaBV | |
| Bracoviriform indiense | Glyptapanteles indiensis bracovirus | GiBV | |
| Bracoviriform insularis | Chelonus insularis bracovirus | CinsBV | |
| Bracoviriform kariyai | Cotesia kariyai bracovirus | CkBV | |
| Bracoviriform liparidis | Glyptapanteles liparidis bracovirus | GlBV | |
| Bracoviriform marginiventris | Cotesia marginiventris bracovirus | CmaBV | |
| Bracoviriform melanoscelae | Cotesia melanoscela bracovirus | CmeBV | |
| Bracoviriform nigricipitis | Cardiochiles nigriceps bracovirus | CnBV | |
| Bracoviriform ornigis | Pholetesor ornigis bracovirus | PoBV | |
| Bracoviriform paleacritae | Protapanteles paleacritae bracovirus | PpBV | |
| Bracoviriform quadridentatae | Ascogaster quadridentata bracovirus | AqBV | |
| Bracoviriform rubeculae | Cotesia rubecula bracovirus | CrBV | |
| Bracoviriform schaeferi | Cotesia schaeferi bracovirus | CsBV | |
| Bracoviriform texani | Chelonus texanus bracovirus | CtBV |
Viruses in Bracovirus are enveloped, with prolate ellipsoid and cylindrical geometries. Genomes are circular and segmented, around 2.0-31kb in length. The genome of the virus is enveloped with 35 double stranded DNA (dsDNA) all of which are circular.[4]
| Genus | Structure | Symmetry ! | Capsid | Genomic arrangement | Genomic segmentation | |
|---|---|---|---|---|---|---|
| Bracovirus | Prolate ellipsoid | Enveloped | Circular | Segmented |
Viral replication is nuclear. DNA-templated transcription is the method of transcription. The virus exits the host cell by nuclear pore export. Transmission routes are parental.
The replication of the Bracoviriform occurs within the ovaries of a parasitic wasps in calyx cells and is maintained by vertical transmission and to go into further detail the packaged genome of dsDNA is replicated inside of the wasp ovaries by development of the sequences of the virus from proviral segments in the tandem arrays in the wasp genome. The development of the sequences of Bracoviriform shows head-to-head and tail-to-tail sequences, which is unexpected, given that it has evolved from the nudivirus [4] The research conducted on Cotesia congregata shows that the viral genome contains one to three proviral segments.[4]
The virus like particle is transmitted into a lepidopteran host (a caterpillar) and infects and manipulates the physiology of the caterpillar so that it can be used as a living incubator for wasp larvae. When this happens the virus disrupts the caterpillar's immune system causing paralysis and inhibiting the pupating of the host. The arresting of the host increases the chance of success of the wasp larva developing successfully.[1]