Classifying bracoviruses, ichnoviruses and virus-like particles

Wasps are rarely regarded as endearing creatures, but perhaps none less so than parasitoid wasps. Parasitoid wasps are a large family of wasp species that implant their eggs or larvae in or on the bodies of certain insect hosts, eventually leading to the death of that insect. 

This implantation becomes deadly with the assistance of bracoviruses, ichnoviruses and virus-like particles found in the wasps. Bracoviruses were integrated into the Braconidae family of wasps around 100 million years ago and are now found in around 50,000 wasp species while ichnoviruses are found in a few thousand species within the Ichneumonidae family of wasps. Unlike most other viruses where the entire genome of the virus is transmitted to evoke an infection, DNA fragments produced by the viruses are passed on to the offspring of the wasp while also resulting in the successful infection of a host. 

These viruses have formed a mutualistic relationship with the wasps and cause them no harm. However, when the wasps deposit their offspring in or on the body of the host insect, the virus particles are discharged with them and begin to inhibit the immune system of the host and protect the wasp offspring. This allows the wasp brood to mature and deplete the nutrients of the host without being ejected.

These viruses are currently classified as endogenous virus elements (EVEs), which is a classification referring to viral DNA fragments that have been incorporated into the DNA of organisms. These EVEs typically become inactive shortly after incorporation into an organism’s genome, but can be beneficial to the organism by providing protection from disease infection or adapting to perform new functions.

However, a team of authors, including CEID researcher Michael Strand, suggest ichnoviruses, bracoviruses and virus-like particles would be better described as domesticated endogenous viruses (DEVs) due to a few key differences from EVEs. 

While EVEs are considered to be simplistic and rarely able to behave like viruses, DEVs retain their complexity and function as viruses. Given that ichnoviruses, bracoviruses and virus-like particles are elaborate and still lead to successful infection in the host when the wasp’s offspring are released, the authors of this paper believe it is more accurate to classify these viruses as DEVs to recognize their complexity.

This more accurate classification of the viruses can aid in prioritizing the remaining research questions regarding the viruses and how they’re incorporated into the genomes of wasps. It may also provide a framework to identify other viruses that may be examples of domesticated viruses.

To read more about this research, click here.

By Amanda Budd