An article published on Sept. 9 identified a specific viral gene that drives infected caterpillars to die in a way that offers the best potential for spreading the virus that killed it, scientists say.

Dr. Kelli Hoover of Pennsylvania State University, led the study, which was published in Science, a journal of the American Association for the Advancement of Science.

Hoover explained that the discovery provides evidence of a genetic basis for a parasite's ability to have an effect on the host behavior, which scientists called the extended phenotype.

Team members included other Pennsylvania State University researchers and scientists with the Harvard Medical School.

The identification of a specific viral gene that causes the extended phenotype allows other researchers working in this area to narrow their search for the genes that may be responsible in their system, according to Slavicek.

Baculoviruses are viruses that are used to infect and kill the caterpillars of insect pests of trees and crops, one of which kills larvae of the gypsy moth, an urban and forest tree pest in northeastern states that defoliates trees, study authors noted.

This virus is specific for the gypsy moth, and consequently will not impact any other insect, animal, or plant in the treatment area.

The Northern Research Station and the USDA Animal and Plant Health Inspection Service (APHIS) are partners in producing the virus for states, the National Park Service and other agencies to use to control gypsy moths.

A healthy gypsy moth caterpillar feeds at night and either hides in a tree's bark crevices during the day or climbs down the tree to the soil to avoid predators.

Who knew that a virus could change the behavior of its host? Slavicek said. Maybe this is why we go to work when we have a cold.

For the virus behind tree top disease, there is a significant advantage to a caterpillar dying in the middle of a leaf within the canopy of the tree rather than in a crevice.

The dead caterpillar liquefies, releasing millions of virus particles into the environment where they can spread throughout the tree and contaminate other gypsy moth larvae.

Watch Zombie Caterpillar Video Below: