science

Polydnaviriformidae

Polydnaviriformidae is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Polydnaviriformidae rather than just read about it. In short: Polydnaviriformidae ( PDV) is a family of insect viriforms; members are known as polydnaviruses. There are two genera in the family: Bracoviriform and Ichnoviriform.

Key takeaways

Polydnaviriformidae belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Polydnaviriformidae to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Polydnaviriformidae from memory before moving on to harder problems.

Reference excerpt

Polydnaviriformidae ( PDV) is a family of insect viriforms; members are known as polydnaviruses. There are two genera in the family: Bracoviriform and Ichnoviriform. Polydnaviruses form a mutualitic relationship with parasitoid wasps. Ichnoviriforms (IV) occur in Ichneumonid wasps and Bracoviriforms (BV) in Braconid wasps. The larvae of wasps in both of those groups are themselves parasitic on Lepidoptera (moths and butterflies), and the polydnaviruses are important in circumventing the immune response of their parasitized hosts. Little or no sequence homology exists between BV and IV, suggesting that the two genera have been evolving independently for a long time.

Taxonomy Bracoviriform

Ichnoviriform

Structure Viruses in Polydnaviridae are enveloped, with prolate ellipsoid and cylindrical geometries. Genomes are circular and segmented, composed of multiple segments of double-stranded, superhelical DNA packaged in capsid proteins. They are around 2.0–31kb in length.

Life cycle Viral replication is nuclear. DNA-templated transcription is the method of transcription. The virus exits the host cell by nuclear pore export. Parasitoid wasps serve as hosts for the virus, and Lepidoptera serve as hosts for these wasps. The female wasp injects one or more eggs into its host along with a quantity of virus. The virus and wasp are in a mutualistic symbiotic relationship: expression of viral genes prevents the wasp's host's immune system from killing the wasp's injected egg and causes other physiological alterations that ultimately cause the parasitized host to die. Transmission routes are parental.

Biology

These viruses are part of a unique biological system consisting of an endoparasitic wasp (parasitoid), a host (usually lepidopteran) larva, and the virus. The full genome of the virus is endogenous, dispersed among the genome of the wasp. The virus only replicates in a particular part of the ovary, called the calyx, of pupal and adult female wasps. The virus is injected along with the wasp egg into the body cavity of a lepidopteran host caterpillar and infects cells of the caterpillar. The infection does not lead to replication of new viruses; rather, it affects the caterpillar's immune system, as the virion carries virulence genes instead of viral replication genes. It can be considered a type of viral vector. Without the virus infection, phagocytic hemocytes (blood cells) will encapsulate and kill the wasp egg and larvae, but the immune suppression caused by the virus allows survival of the wasp egg and larvae, leading to hatching and complete development of the immature wasp in the caterpillar. Additionally, genes expressed from the polydnavirus in the parasitised host alter host development and metabolism to be beneficial for the growth and survival of the parasitoid larva.

Potential carrier subfamilies Ichneumonoidea Braconidae Microgastrinae Miracinae Cheloninae Cardiochilinae Mendeselinae Khoikhoiinae Ichneumonidae Campopleginae Banchinae

Characteristics Both genera of PDV share certain characteristics:

the virus particles of each contain multiple segments of dsDNA (double-strand, or "normal" DNA, as contrasted with positive- or negative-sense single-strand DNA or RNA, as found in some other viruses) with each segment containing only part of the full genome (much like chromosomes in eukaryotic organisms) the genome of the virus has eukaryotic characteristics such as the presence of introns (common for insect genes but rare for viruses) and a low coding density the genome of each virus is integrated into the host wasp genome the genome is organized in several multiple-member genes families (which differ between Bracoviruses and Ichnoviruses) the virus particles are only produced in specific cell types in the female wasp's reproductive organs The morphologies of the two genera are different when observed by electron microscopy. Ichnoviruses tend to be ovoid while bracoviruses are short rods. The virions of Bracoviruses are released by cell lysis; the virions of Ichnoviruses are released by budding.

Evolution Nucleic acid analysis suggests a very long association of the viruses with the wasps (estimated 73.7 million years ± 10 million).

Older wasp-derived theory Two proposals have been advanced for how the wasp/virus association developed. The first suggests that the virus is derived from wasp genes. Many parasitoids that do not use PDVs inject proteins that provide many of the same functions, that is, a suppression of the immune response to the parasite egg. In this model, the braconid and ichneumonid wasps packaged genes for these functions into the viruses—essentially creating a gene-transfer system that results in the caterpillar producing the immune-suppressing factors. In this scenario, the PDV structural proteins (capsids) were probably "borrowed" from existing viruses.

Current endogenous virus theory

The alternative proposal suggests that ancestral wasps developed a beneficial association with an existing virus that eventually led to an endogenization of the virus into the wasp's genome. Following integration, the genes responsible for virus replication and the capsids were (eventually) no longer included in the PDV genome. This hypothesis is supported by the distinct morphology differences between IV and BV, suggesting different ancestral viruses for the two genera. BV has likely evolved from a nudivirus, specifically a betanudivirus, ~100 million years ago. IV has a less clear origin: although earlier reports found a protein p44/p53 with structural similarities to ascovirus, the link was not confirmed in later studies. As a result, the current opinion is that IV originated from a yet-unidentified novel viral family, with a weak link to the NCLDVs. In either case, both genera were formed through a single integration event in their respective wasp lineages. The two groups of viruses in the family are not in fact phylogenetically related suggesting that this taxon may need revision.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Polydnaviriformidae

Start with the simplest possible case. Write down what Polydnaviriformidae claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Polydnaviriformidae before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Polydnaviriformidae ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Polydnaviriformidae

In research: Polydnaviriformidae appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Polydnaviriformidae in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Polydnaviriformidae is common in secondary-school and first-year university syllabi. It links to neighbouring topics Polydnaviridae, Symbiosis, so understanding it makes those chapters shorter.
In everyday life: Look for Polydnaviriformidae outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Polydnaviriformidae” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Polydnaviriformidae in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Polydnaviriformidae means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Polydnaviriformidae out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Polydnaviriformidae in simple terms?

Polydnaviriformidae ( PDV) is a family of insect viriforms; members are known as polydnaviruses. There are two genera in the family: Bracoviriform and Ichnoviriform.

Why does Polydnaviriformidae matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Polydnaviriformidae?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Polydnaviriformidae.