Natural Enemies
virus killed larva
Steven Katovich,
USDA Forest Service, Bugwood.org
There are many natural enemies of gypsy moth in Virginia. Parasitoids and predators help to control gypsy moth at low population levels. The fungal disease Entomophaga maimaiga is effective at both low and high densities of gypsy moth, while the viral disease (gypsy moth nucleopolyhedrosis virus, or NPV) is effective at high population densities. It is this viral disease that usually causes high gypsy moth populations to crash. It is not unusual to see large numbers of dead caterpillars, killed by either the fungus or virus, hanging on the bole of trees.
white-footed mouse
Perhaps the most effective non-disease control agent is the white-footed mouse. Indeed, some studies indicate that the relationship among mice, acorn abundance, and gypsy moth has an effect on gypsy moth population cycles. In addition to mice, shrews, birds, ants, and ground beetles all feed on gypsy moth to some degree.
While predators feed on gypsy moth larvae or pupae, certain flies and wasps will parasitize larvae and eggs and this helps to maintain low populations. One of the most common insect parasitoids is a tiny wasp, Ooencyrtus kuvanae, which lays its eggs in gypsy moth eggs within the egg mass. O. kuvanae has several generations per year, and thus gypsy moth egg masses laid in late summer will often show tiny exit holes where O. kuvanae adults have emerged from the gypsy moth eggs. This can occur in the same season and the presence of these exit holes does not mean the egg masses are from an earlier season and have already hatched.
It should be remembered that while natural controls are important in gypsy moth population dynamics, they do not prevent outbreaks. There are many factors that influence gypsy moth population cycles, and outbreaks will occur periodically even in the presence of natural controls. This is especially true for the fungus, E. maimaiga, since this organism is very dependent on specific weather conditions for growth and distribution.
Ooencyrtus kuvanae on egg mass