Two related issues in studies of biological
invasions are how quickly the enemy complexes of
invasive species become as species-rich and efficient
as those of native species and how important enemy
release is for the establishment and spread of invaders.
We addressed these issues for the geometrid moths
Operophtera brumata and Agriopis aurantiaria, who
invaded the coastal mountain birch forest of northern
Norway by range expansion approximately a century
and 15 years ago, respectively. This was done by
comparing larval parasitoid species richness and
prevalence among the invaders and the native geometrid
Epirrita autumnata. We found that E. autumnata
and O. brumata both hosted seven parasitoid species
groups, whereas A. aurantiaria hosted only one.
Several parasitoid groups were shared between two
or more of the geometrids. Total larval parasitism rates
were similar in all three geometrid species, and
comparison with published studies on larval parasitism
in Western Europe suggested that O. brumata and
A. aurantiaria do not suffer lower parasitism rates in
our study region than in their native ranges. Our results
indicate that accumulation of larval parasitoids on
invasive geometrids in coastal mountain birch forest
may reach completion within a few decades to at least
a century after the invasion, and that establishment and
spread of such invaders is unlikely to be facilitated by
release from larval parasitism. Our investigations also
uncovered a high degree of spatiotemporal synchrony
between the total larval parasitism rates of O. brumata
and A. aurantiaria, suggesting that larval parasitism of
different geometrid species in the study system is
governed by some common external factor
