Scientists have isolated a viral gene that induces zombie-like behavior — in caterpillars. The virus causes gypsy moth caterpillars to climb to the tops of trees, where they die and their disintegrating bodies rain infectious particles on their unsuspecting brethren below.
The discovery, published in Friday's edition of the journal Science, highlights a singular pathogen gene that manipulates the behavior of its host.
Researchers had long commented on the odd behavior of caterpillars infected by the virus, dubbed LdMNPV (short for Lymantria dispar nucleopolyhedrovirus). Typically, caterpillars travel down tree trunks in the daytime to avoid predators. But the sickened crawlers headed in the other direction, meeting their deaths in the tree canopy.
"You end up with this sack of virus that opens up," said lead author Kelli Hoover, an entomologist at Pennsylvania State University. "It melts and it's gooey and you get [a trillion] of them raining down and spreading down on the leaves. It's a very efficient virus."
Was this just coincidence, or was the virus able to control its host's behavior for maximum delivery?
To find out, Hoover and her colleagues homed in on a gene called egt that was suspected of being the culprit for the caterpillars' strange behavior. The gene produces a hormone that keeps the caterpillar from molting. When the caterpillar molts, it stays put for a while instead of traveling up the tree to eat, Hoover said.
The researchers infected caterpillars with three versions of the virus — one with the normal egt gene, one in which egt had been removed, and a third in which egt had been removed and reinserted.
Sure enough, caterpillars infected with egt-armed viruses climbed much higher before dying — allowing the pathogen to achieve maximum viral delivery. Caterpillars infected with the egt-free viruses died at low elevations, putting those viruses at a competitive disadvantage.
"It's surprising you could alter such a major behavior," said Glenn McConkey, a parasitologist at the University of Leeds in England, who wasn't involved in the study. "It opens up a question of whether this gene might have similar functions in other viruses."