Kelli Hoover and her research team have identified the viral gene responsible for inducing “tree top disease” in gypsy moths.
By: Seth Palmer
"Tree top disease" causes caterpillars to forgo molting and climb to the treetops, where they remain until they die.
The team deduced that the disease is induced by the baculoviral gene egt encoding the enzyme EGT in the caterpillars, which inactivates the molting hormone 20E.
Normally, gypsy moth caterpillars feed in the canopy at night and return below during the day to hide in the soil or in crevices in the bark.
But when 20E is inactivated, the caterpillars remain in a constant feeding state in the treetops where they eventually die, liquefy and rain down viral particles on the leaves and new hosts below.
Dr. Hoover stressed the benefit to the virus of its hosts continuing to eat rather than fasting in preparation for molting – the caterpillars maximize the amount of biomass available for viral replication.
She also emphasized that the virus seems to compel its hosts to travel to locations that are optimal for its transmission to new hosts.
Older caterpillars infected with the virus die on the bark near where others will come to pupate.
The emerging gypsy moths contact the virus upon leaving their cocoons, and pass it to their offspring when they lay their eggs.
Dr. Hoover noted that, published in the September 9 issue of Science, is one of the first studies to identify the specific gene in a parasite that is responsible for altering the behavior of the host organism.
About the researchers
David Hughes is an assistant professor of entomology and biology at Penn State, a faculty member of the Huck Institutes' graduate program in ecology, and a researcher in the Center for Brain, Behavior and Cognition and the Center for Infectious Disease Dynamics.