Virus grants wasps longer life

A newly discovered virus tinkers with its wasp host’s longevity and sex, researchers have discovered.

The virus infects a chalcid wasp called Pteromalus puparum, a parasitoid. This means it lays its eggs in other living insects. Butterfly caterpillars are a particular favourite.

A team led by Gongyin Ye from Zhejiang University in China discovered the virus when trawling through the wasp’s transcriptome – a read-out of the wasp’s active genes. The team noted that one of the read-outs didn’t belong to the wasp, but to a virus.

Wasps and viruses often form symbiotic alliances against their insect hosts. For example, some wasps need particular viruses in order to produce the pathogens necessary to defeat host-insect immune systems and thus boost survival chances for implanted eggs.

Ye’s team recognised the previously unknown virus as a member of the family Nyamiviridae. They dubbed it Pteromalus puparum negative-strand RNA virus 1, or PpNSRV-1 for short.

The researchers wanted to find out whether it confers any advantages on the wasp – and it turns out that it does, at least in the laboratory.

Wasps infected with the virus lived about a third longer than uninfected ones. It’s not yet known whether this effect will hold for wasps in the wild – where the team found infection rates running between 17% and 38% – but if it does, it could suggest a nifty evolutionary strategy on the part of both partners: the longer the wasp lives, the greater its opportunity to spread the virus.

But that’s not all the virus does. It also skews the sex ratio of the wasps, reducing by around half the number of females that hatch.

“It’s quite unusual,” says entomologist Ary Hoffmann from the University of Melbourne, who was not involved in the study. Whereas there are several examples of insect-infecting bacteria that kill males, he says, “here we have an example of a virus that seems to be doing the opposite”.

Teasing out the virus’s effects in wild wasp populations and butterfly hosts will require further work.

According to Hoffman, the study highlights the staggering diversity of insect infections, both viral and bacterial, that are only now coming to light thanks to advances in molecular sequencing techniques.

“There is this amazing biodiversity of [insect] viruses out there and we really don’t know much about them,” he says.

The research is published in PLOS Pathogens.