As with most insects, various parasitoid species attack the different life stages of gypsy moth. In North America, efforts to introduce parasitoids of gypsy moth from Europe and Asia began around 1905, and 10 species have been established. The egg parasitoid Ooencyrtus kuvanae (Encyrtidae) from Japan is frequently observed on gypsy moth egg masses in late summer and may cause as much as 30% mortality of the eggs. Larval parasitoids include Cotesia melanoscela (Braconidae) and the tachinids Blepharipa pratensis, Compsilura concinnata, and Parasetigena silvestris. The most common pupal parasitoid is Brachymeria intermedia (Chalcididae). The impact of these parasitoids on gypsy moth populations remains equivocal. Total mortality caused by parasitoids in North America is typically below 50% and is not consistently density dependent, so that their ability to regulate gypsy moth populations is in doubt. In Europe, on the other hand, parasitism of gypsy moth is often much higher than that observed in North America. European gypsy moths are attacked by several parasitoid species that were never established successfully in North America. It seems likely that parasitoids are responsible for preventing gypsy moth outbreaks, which are rare in western Europe, but more common in central and southern Europe.

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