Viral disease, sometimes referred to as "wilt",
is naturally ocurring in virtually all gypsy moth
The Disease is caused by a nucleopolyhedrosis virus (NPV).
This name is derived by the existence of a a matirix of
polyhedral protiens that surround the viral DNA.
These polyhedra are large and can be seen under a light
Infection occurrs when caterpillars
eat foliage contaminated with viral oclusion bodies.
This pathogen invades through the gut wall, reproducing rapidly
in internal tissue causing the disintegration of internal
organs and the death of the host caterpillar.
Eventually, the host ruptures, distributing
viral oclusion bodies into the environment which serve
to infect other individuals.
Virus particles can persist in the soil.
Virus can persist in low density gypsy moth populations
but causes very little mortality when populations are low.
However, when gypsy moth populations are high,
massive propogation of virus occurrs, resulting in very
high levels of host mortality.
This phenomenon is called an "epizootic" and is the
most common cause of the collapse of high density gypsy
There has been considerable research that has gone on
to develop the gypsy moth NPV as a biological pesticide.
This material, referred to as
is currently used in limitted quantities for suppressing
gypsy moth outbreaks.
Gypsy moth virus life cycle: viral occlusion bodies (OB)
(A) dissolve in the insect's gut liberating nonoccluded virus (NOV) that enters the midgut
(B) and eventually passes through to the hemocoel. There NOV enters hemocytes and other cell types and replicates
(C), producing more NOV (D) and OB (E). Cells eventually rupture releasing
NOV and OB into the hemocoel.
The insect dies (F) 10-14 days after consuming the virus.
(photo from Reardon, Podgwaite, Zerillo. 1996. Gypcheck - The Gypsy Moth
Nucleopolyhedrosis Virus Product. USDA FS FHTET-96-16.)