from Cornell University:
Gypsy moths wreak havoc, but their own enemies
are not far behind.
See all of those brown streaks hanging on the bark
of the oak tree? They are Gypsy moth caterpillars
killed by the fungal pathogen Entomophaga maimaiga.
courtesty of USDA.
ITHACA, N.Y. – If you live in a section of the
country where gypsy moths are a relatively new menace, have no fear, help is
not far behind.
Cornell University entomologist Ann Hajek told a
national conference earlier this month that when the gypsy moth – whose
caterpillars have defoliated entire forests – started spreading westward more
than 100 years ago from New England to Wisconsin, its fungal and viral pathogens
followed close behind.
“We were pretty surprised,” Hajek says. “No one
knew how long it took the pathogens to chase their hosts.”
The findings are important because gypsy moth
populations can develop unpredictably and erratically, with lots of
caterpillars eating all the leaves off of most of the trees, Hajek told attendees
at the Cornell-hosted Eighth Annual Ecology and Evolution of Infectious Disease
workshop and conference, June 3-4, in Ithaca. Land managers, she says, can rest
assured that pathogens will follow the migrating moths, providing natural
Gypsy moths are slowly moving west across the
United States after being introduced to Massachusetts from Europe in 1869. They
migrate slowly because the females do not fly. By tracking the edges of the
migration, where population densities are low, researchers have an opportunity
to investigate how long it takes their viral and fungal pathogens to catch up,
The fungal pathogen, entomophaga maimaiga, was first reported in 1989 and attacks the
caterpillars. The virus, lymantria dispar
nucleopolyhedrovirus, which was accidentally introduced near Boston in
1906, also infects gypsy moth caterpillars.
Hajek and colleagues studied “leading edge”
populations of moths and pathogens in central Wisconsin in 2005-07. They set
pheromone traps west of the migrating population and then traveled east to lay
traps to catch the flying males. Once their traps caught more than 74 moths
each in single year, there was a more than 50 percent chance of finding the
fungus in that area in the following year. When more than 252 moths were
trapped in a year, there was more than 50 percent chance of finding the virus
the next year.
“Our data show that the fungus spreads into lower
density leading edge populations sooner than the virus, but the virus
eventually colonizes the populations, too,” Hajek says.
Fungal spores actively shoot out of the moth
cadavers and disperse in the environment, thereby spreading quickly. The virus
spreads from one caterpillar to another, and possibly via parasitoid flies and
predators, which is a slower process, she said.
Hajek has also discovered that the efforts of land
managers to release the pathogens along the leading edges of spreading moth
populations are ineffective and unnecessary. Hajek and colleagues found no
association between the release of pathogens nearby and presence of the
pathogens among the moths.
“These results suggest that the pathogens are
dispersing on their own and land managers don't need to release them in leading
edge gypsy moth populations, because they'll get there on their own anyway,”
The conference was sponsored by the Cornell
University Center for a Sustainable Future, Institute for Computational
Sustainability, National Science Foundation and Cornell.