Large areas of forests are annually damaged or destroyed by outbreaking
insect pests. Understanding the factors that trigger and terminate such
population eruptions has become crucially important, as plants,
plant-feeding insects, and their natural enemies may respond
differentially to the ongoing changes in the global climate. In
northernmost Europe, climate-driven range expansions of the geometrid
moths Epirrita autumnata and Operophtera brumata have resulted in
overlapping and increasingly severe outbreaks. Delayed density-dependent
responses of parasitoids are a plausible explanation for the ten-year
population cycles of these moth species, but the impact of parasitoids
on geometrid outbreak dynamics is unclear due to a lack of knowledge on
the host ranges and prevalences of parasitoids attacking the moths in
nature. To overcome these problems, we reviewed the literature on
parasitism in the focal geometrid species in their outbreak range, and
then constructed a DNA barcode reference library for all relevant
parasitoid species based on reared specimens and sequences obtained from
public databases. The combined parasitoid community of E. autumnata and
O. brumata consists of 32 hymenopteran species, all of which can be
reliably identified based on their barcode sequences. The curated
barcode library presented here opens up new opportunities for estimating
the abundance and community composition of parasitoids across
populations and ecosystems based on mass barcoding and metabarcoding
approaches. Such information can be used for elucidating the role of
parasitoids in moth population control, possibly also for devising
methods for reducing the extent, intensity, and duration of outbreaks.