Dinocampus coccinellae paralysis virus (DcPV) is a single-stranded,

positive-sense In molecular biology and genetics, the sense of a nucleic acid molecule, particularly of a strand of DNA or RNA, refers to the nature of the roles of the strand and its complement in specifying a sequence of amino acids. Depending on the context, ...

RNA virus An RNA virus is a virus characterized by a ribonucleic acid (RNA) based genome. The genome can be single-stranded RNA (ssRNA) or double-stranded (Double-stranded RNA, dsRNA). Notable human diseases caused by RNA viruses include influenza, SARS, ...

of insects, in the picorna-like virus family ''

Iflaviridae ''Iflaviridae'' is a family of positive sense RNA viruses insect-infecting viruses. Some of the insects commonly infected by iflaviruses include aphids, leafhoppers, flies, bees, ants, silkworms and wasps. The name "Ifla" is derived from the ...

'', which was first characterised in 2015. It asymptomatically infects the parasitic

braconid wasp The Braconidae are a family of parasitoid wasps. After the closely related Ichneumonidae, braconids make up the second-largest family in the order Hymenoptera, with about 17,000 recognized species and many thousands more undescribed. One analysis ...

, '' Dinocampus coccinellae'', and has been proposed to be associated with the paralytic effect the wasp has on its host, the spotted lady beetle, ''

Coleomegilla maculata ''Coleomegilla maculata'', commonly known as the spotted lady beetle, pink spotted lady beetle or twelve-spotted lady beetle, is a large coccinellid beetle native to North America. The adults and larvae feed primarily on aphids and the species ...

'', which it turns into a so-called "zombie bodyguard" for its

pupa A pupa (; : pupae) is the life stage of some insects undergoing transformation between immature and mature stages. Insects that go through a pupal stage are holometabolous: they go through four distinct stages in their life cycle, the stages th ...

Taxonomy

Within the family ''Iflaviridae'', the DcPV genome is most closely related to ''Venturia canescens'' picorna-like virus and ''Nasonia vitripennis'' virus-1.

Distribution

DcPV has been found in ''D. coccinellae'' from Canada, Japan, Poland and the Netherlands.

Structure

DcPV's 10,138 nucleotide linear RNA has a single large

open reading frame In molecular biology, reading frames are defined as spans of DNA sequence between the start and stop codons. Usually, this is considered within a studied region of a prokaryotic DNA sequence, where only one of the six possible reading frames ...

, predicted to encode a 3007 residue polyprotein with non-structural

helicase Helicases are a class of enzymes that are vital to all organisms. Their main function is to unpack an organism's genetic material. Helicases are motor proteins that move directionally along a nucleic double helix, separating the two hybridized ...

protease A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalysis, catalyzes proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the formation of new protein products ...

and

RNA-dependent RNA polymerase RNA-dependent RNA polymerase (RdRp) or RNA replicase is an enzyme that catalyzes the self-replication, replication of RNA from an RNA template. Specifically, it catalyzes synthesis of the RNA strand Complementarity (molecular biology), compleme ...

functions in the C-terminal portion and four structural proteins (VP1–4) in the N-terminal portion. The 5′ non-translated region contains cloverleaf and hairpin structures similar to those present in picornaviruses and other picorna-like viruses. The virus particle is around 27 nm in diameter.

Viral life cycle in ''D. coccinellae''

DcPV has not been detected in ''D. coccinellae'' eggs. After hatching, the level of the virus genome increases throughout the larval stages, where active viral replication is thought to occur. Higher levels are found in adult wasps, considered to represent inactive stocks of virus. The virus particles are located within large

vesicles Vesicle may refer to: ; In cellular biology or chemistry * Vesicle (biology and chemistry), a supramolecular assembly of lipid molecules, like a cell membrane * Synaptic vesicle In a neuron, synaptic vesicles (or neurotransmitter vesicles) s ...

in cells lining the female wasp's

oviduct The oviduct in vertebrates is the passageway from an ovary. In human females, this is more usually known as the fallopian tube. The eggs travel along the oviduct. These eggs will either be fertilized by spermatozoa to become a zygote, or will dege ...

, where they are sometimes observed to form crystalline arrays. The virus has not yet been shown to cause any disease in the wasp, and the two might have a

symbiotic Symbiosis (Ancient Greek : living with, companionship < : together; and ''bíōsis'': living) is any type of a close and long-term biolo ...

relationship.

Putative effect of DcPV on ''C. maculata''

The ''Dinocampus coccinellae'' wasp parasitises the lady beetle species ''

''. The wasp lays a single egg in the beetle's

haemocoel In vertebrates, the circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the body. It includes the cardiovascular system, or vascular system, that consists of the heart an ...

where the larva develops, to emerge approximately 20 days later. The wasp larva then

tes with its cocoon underneath the living body of the beetle host. At this point the lady beetle host, which has previously behaved normally, stops moving, is afflicted with twitches or tremors, and becomes a semi-paralysed guardian of the wasp cocoon – often referred to as a "zombie bodyguard" – until the adult wasp emerges a week later. Around a quarter to a third of lady beetles subsequently recover. The exact cause of this dramatic alteration in the beetle's behaviour is unknown, however there is an observation of neuropathy in the ladybug owing to the neurotropic nature of the virus. There is also observation of the downplaying of genes such as Dicer , Ago2, Tlr7 and PI3K.(Both Dicer and Ago2 are involved in gene expression in the organism). At the time it occurs the parasite and host are no longer in direct contact, as the wasp pupates externally to the lady beetle. Nolwenn Dheilly and co-workers have suggested that the mechanism involves DcPV; some other experts consider that the evidence for this is incomplete. DcPV appears to be transmitted to the lady beetle during wasp larval development, with viral RNA being present in the abdomen and head of parasitised lady beetles, but absent from resistant beetles in which the wasp larvae fail to develop. In beetles that recover from paralysis, the level of virus declines significantly. Virus particles, together with

lipid Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include storing ...

droplets, have been observed in

glial cell Glia, also called glial cells (gliocytes) or neuroglia, are non-neuronal cells in the central nervous system (the brain and the spinal cord) and in the peripheral nervous system that do not produce electrical impulses. The neuroglia make up ...

s of the

cerebral Cerebral may refer to: * Of or relating to the brain * Cerebrum, the largest and uppermost part of the brain * Cerebral cortex, the outer layer of the cerebrum * Retroflex consonant, also referred to as a cerebral consonant, a type of consonant so ...

ganglia A ganglion (: ganglia) is a group of neuron cell bodies in the peripheral nervous system. In the somatic nervous system, this includes dorsal root ganglia and trigeminal ganglia among a few others. In the autonomic nervous system, there a ...

in parasitised lady beetles. After the wasp larva emerges from the beetle, signs of

neuropathy Peripheral neuropathy, often shortened to neuropathy, refers to damage or disease affecting the nerves. Damage to nerves may impair sensation, movement, gland function, and/or organ function depending on which nerve fibers are affected. Neuropa ...

develop including numerous

vacuole A vacuole () is a membrane-bound organelle which is present in Plant cell, plant and Fungus, fungal Cell (biology), cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water ...

s in the beetle glial cells. Dheilly and co-workers speculate that this nervous tissue damage is caused by the beetle's immune response and that it mediates the observed change in behaviour, characterising the virus as a "

biological weapon Biological agents, also known as biological weapons or bioweapons, are pathogens used as weapons. In addition to these living or replicating pathogens, toxins and Toxin#Biotoxins, biotoxins are also included among the bio-agents. More than 1,2 ...

" deployed by the wasp against the beetle.

References