LARVAL PARASITISM IN OUTBREAKING AND NON-OUTBREAKING POPULATIONS OF EPIRRITA-AUTUMNATA (LEPIDOPTERA, GEOMETRIDAE)

Larval parasitism of Epirrita autumnata (Borkhausen) was monitored dur ing six years in field samples from within the outbreak range of E. au tumnata in northern Fennoscandia, and outside it in southern Finland. All parasitoids found were hymenopterans. Six phenologically early spe cies of parasitoids were found in populations within the outbreak rang e and three species outside the outbreak range. Two late larval parasi toid species were found within the outbreak range, but none outside th e outbreak range. In half of the populations within the outbreak range , early larval parasitoids seemed to increase with a time lag. This is consistent with the cyclic population fluctuations of E. autumnata th ere. On a small spatial scale (among trees), however, parasitoids acte d without a time lag. Parasitism rates by the early larval parasitoids are probably too low (mean 11%) for early parasitoids alone to keep d ensities of E. autumnata continuously at low levels outside the outbre ak range in southern Finland.