How a Virus Mothballs

The infected caterpillar is forced upwards onto a tree, where it liquefies and drips down to infect other caterpillars

A couple of months ago, we reported the strange case of a fungus that manipulates an ant for its own survival. The parasitic fungus forces the ant downwards through the rainforest canopy to its death at a shady spot best suited for the fungus to reproduce. According to a recent paper published in Science, it seems that reported fungus is not alone in forcing a more complex living organism to do its bidding; a virus seems to force similar behaviour on the European gypsy moth caterpillar. The difference is that, rather than being driven down, the infected caterpillar is driven up onto a tree and then onto a leaf, behaviour it would normally avoid during the day.

According to a news release, the scientists identified ‘a specific viral gene, EGT, that codes for an enzyme… that inactivates the hormone that triggers molting. Male gypsy moth caterpillars molt five times during their lives, while females molt six times before they pupate and emerge as moths. But infected caterpillars do not molt again once levels of EGT become high enough. EGT induces the caterpillar to climb to the treetops, hang onto the leaf or bark with their prolegs and die. Then, they liquefy and rain viral particles over the leaves for other caterpillars to ingest and become infected. Older caterpillars are induced to die on the bark next to their fellow gypsy moths that pupate and emerge to walk over the dead cadavers, picking up virus that can be transmitted to the next generation during egg laying…’

‘The researchers tested six different virus infected groups of caterpillars and one uninfected group. Two groups were infected with different, naturally occurring virus; two groups were infected with virus that had their EGT gene inactivated… and two groups had the EGT gene reinserted in the viral DNA. The two naturally occurring viruses caused the caterpillars to climb and die at the top of the container, but the caterpillars infected with virus lacking the EGT gene died at the bottom of the container. The caterpillars with the restored EGT gene also died at elevated positions.’

About The Author

Hartosh Singh Bal