Vertebrate predators such as birds account for most of the mortality in low density populations, so any disruption of bird habitat, especially food sources, will affect this predation. Other predators are more significant mostly at higher moth densities than we have in Washington. A partial list is:
- Entomophaga maimaiga is a fungus that attacks the caterpillars.
- Ooencyrtus kuvanae is a wasp that attacks the eggs.
- Cotesia melanoscela is another wasp that attacks the pupae.
- NPV (a virus) attacks dense populations.
The generally accepted hypothesis about natural regulation of gypsy moth populations has been that at low densities, the most important mortality factors are vertebrate predators, at medium densities parasitoids are most important (usually Diptera or Hymenoptera), and at high densities, the gypsy moth nuclear polyhedrosis virus (NPV), a baculovirus, is the most frequent agent regulating populations. NPV causes big crashes in the gypsy moth population (=epizootics) and people often tended to wait for these epizootics to control high populations.
– Ann E. Hajek (Department of Entomology, Cornell University)
This statement can be verified by anyone living in the areas of the eastern US that have been infested with gypsy moth for more than a few decades. In these areas, no lasting damage to plants other than occasional partial defoliation is seen. The gypsy moth populations never reach the extreme peaks seen in the first few years. Most people say they are aware of gypsy moth as an infrequent nuisance but do not describe it as a serious pest.