Butterflies 'steal' genes of parasitic wasps to help them survive

Butterflies 'steal' genes of parasitic wasps to help them survive

Some butterflies and moths have genetically modified themselves by “stealing” the genes of parasitic wasps, scientists have discovered.

The genes are thought to benefit the insects by defending them against harmful viruses.

But the way they are acquired is highly hazardous in itself. The genes are transferred when the wasps lay their eggs in the bodies of host caterpillars.

Usually the caterpillar’s fate is sealed as the wasp larvae hatch and devour their victim from the inside.

However scientists believe in some rare circumstances the host caterpillars survive, transform into butterflies, and breed to pass their wasp genes onto the next generation.

It was also possible that parasitic wasps laid their eggs in non-host species that are immune to the attack but still acquire the genes.

The genes are actually carried in a giant virus, called bracovirus, which is injected into the caterpillar with the parasitic wasp eggs. It helps the wasp by altering the caterpillar’s development to enable its colonisation by the parasitic larvae.

Not only does the virus pass on its own genes, but also those it has picked up from the wasps.

Both kinds of genes have become integrated in the DNA of several species from the Lepidoptera family of butterflies and moths, including the Monarch butterfly and silkworm.

The research, from a joint Spanish and French team, is published in the online journal Public Library of Science Genetics.

Evolutionary biologist Dr Louise Johnson, from the University of Reading, who was not involved in the study, said: “We’ve known for a while that viruses can move genes around between species – we use viruses to do just this in some GM technologies – and we also know that animals can occasionally pick up DNA from their parasites, but this three-way gene shuffle is a particularly clear and clever example: wasps use viruses to attack butterflies, but those viruses have also allowed the butterflies to steal genes from the wasps.

“It’s clear that the stolen genes are useful to the butterflies, so naturally occurring genetic engineering helps them to survive. From my perspective as an evolutionary biologist, it’s also a perfect illustration of how evolution uses every trick in the book, and the book is bigger than we think.”

The scientists said it was likely that what they had seen was “only the tip of the iceberg”.

They added that the findings had implications for pest control strategies using GM parasitic wasps engineered to be resistant to insecticide.

There was a danger that genes for insecticide resistance could be transferred from the wasps to the pests, making them even more destructive.

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