Zombie Caterpillars Created By Single Gene

09/14/2011 10:42 AM ET

Zombie Caterpillars Created By Single Gene, Baculoviruses; Pennsylvania State University lead author Kelli Hoover says that the gene causes gypsy moths to climb the tree tops where they die. After dying, the bodies melt and hang from foliage.

The shower of viral particles then rains down on other caterpillars causing them to do the same thing in a vicious circle.

“You end up with this sack of virus that opens up,” Hoover, an entomologist at Pennsylvania State University, said in a statement. “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.”

The strange behavior was first observed 100 years ago, and was blamed on infection from a virus. Now researchers, led by Hoover, have discovered that a single gene in the baculovirus causes this effect. The gene, named egt, interferes with the caterpillars molting hormone and seems to play a role in the urge to climb.

“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.

In caterpillars, the exoskeleton cannot stretch and thus restricts growth. Arthropods, therefore, replace their exoskeletons by molting, or shedding the old exoskeleton after growing a new one that is not yet hardened. Molting cycles run nearly continuously until an arthropod reaches full size.

Not only does the baculovirus send the caterpillars crawling upward, it also stops them from molting, which is a major help to the virus since molting caterpillars don’t eat, don’t grow, and therefore, produce fewer viruses containing goo. “Who knew that a virus could change the behavior of its host?” study author Jim Slavicek, of the U.S. Forest Service, said in a statement. “Maybe this is why we go to work when we have a cold.”

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