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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 10‐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 recorded 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. [ABSTRACT FROM AUTHOR]

In the present time of biodiversity crisis, assessing species diversity by accurate and accessible taxonomic revisions is more crucial than ever. Parasitoid wasps are considered as both one of the most diverse and under-studied groups in the tree of life. Dusona Cameron, 1901 (Ichneumonidae, Campopleginae) is with 442 species one of the most species - rich genera of Darwin wasps, but despite the existence of recent keys, species identification has proven difficult to impossible to non-specialists. In this study, we examined about 1,500 Dusona specimens from recent and historical collections in Sweden and Switzerland. We provide a photographic guide to diagnostic characters and detailed plates for 57 out of 125 Western Palaearctic Dusona species, facilitating species identification based on existing keys. We add 11 and 3 species to the faunistic records of Sweden and Switzerland, respectively. Furthermore, we reconstruct the phylogeny of European Dusona based on four standard markers (COI, CAD, ITS2, 28S) for 45 species, complemented with a reliable reference barcode library for 46 species. Even though we can identify several morphologically distinct clades, we do not propose any new subgenera due to prevalent homoplasy of characters. While most species are well separated by barcodes, several morphologically distinct species have barely discriminatory barcode sequences (p-distances < 2%) or are even paraphyletic in this marker, indicating limitations in the applicability of barcodes for Darwin wasps. This study reveals severe gaps in the inventories of neglected taxa even for well-studied countries such as Sweden and Switzerland. As this study makes species determination for Western Palaearctic Dusona more accessible, we encourage more people, including non-specialists, to work with this genus. [ABSTRACT FROM AUTHOR]