Two insect parasites, Apanteles harrisinae and Ametadoria
misella, attack western grapeleaf skeletonizer larvae.
A. harrisinae is a parasitic wasp that attacks early larval
instars and usually deposits three to nine eggs in a host. Fully
grown parasite larvae emerge from the fully grown host larva immediately
after it has spun its cocoon. The cocoons are spun within the cocoon
of the host, surrounding the dead caterpillar.
The parasitic fly, A. misella, prefers to attack fourth
and fifth instars. Larviposition occurs during the middle of the
day and larvae immediately penetrate the host. Little development
occurs until the host larva turns into the pupal stage. The parasite
larva then develops rapidly and soon kills the host pupa. Its puparium
is always formed within the host cocoon.