Polydnaviruses

Definition

A family of insect-specific viruses (Polydnaviriformidae) that exist in obligate mutualism with parasitoid wasps, divided into two genera: Bracoviriform (in braconid wasps) and Ichnoviriform (in ichneumonid wasps). These viruses are vertically transmitted and integrated into the wasp genome; they are expressed in the wasp's reproductive tract and injected into lepidopteran hosts during oviposition. Their gene products suppress the host's cellular immune responses—particularly encapsulation reactions—thereby protecting the developing wasp larva from being melanized and killed by the host's hemocytes.

Etymology

From Greek poly- (many) + dna + virus, referring to the multipartite segmented genome composed of multiple circular DNA molecules

Example

The bracovirus Cotesia plutellae polydnavirus encodes proteins that interfere with the diamondback moth's hemocyte spreading and encapsulation behavior, allowing the wasp larva to develop unchallenged within the living host.

Synonyms

• PDV

Related Terms

• Parasitoid
• Encapsulation
• hemocyte
• braconid
• ichneumonid
• host manipulation
• virulence factor
• immune evasion

Usage Notes

The two genera Bracoviriform and Ichnoviriform share no detectable sequence homology, indicating independent evolutionary origins despite convergent functional roles in host immune suppression. The term is sometimes used loosely for the virus particles themselves, though strictly the viruses are not independently replicating entities outside the wasp host. Contrast with pathogenic insect viruses such as baculoviruses, which replicate within and typically kill their hosts.