A curated DNA barcode reference library for parasitoids of northern European cyclically outbreaking geometrid moths

Abstract

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.

A curated DNA barcode reference library for parasitoids of northern European cyclically outbreaking geometrid moths

“…The full dataset including also representative reference sequences from GenBank and BOLD was composed of 198 sequences. Both alignments were 658 bp in length, but species‐specific barcodes were either 640, 643, 652, or 658 bp long, with differences being due to internal deletions of whole codon triplets (data S1 in Nyman et al, 2022 ). The shortest barcodes were found in two Telenomus sequences downloaded from GenBank.…”

“…We obtained parasitoid reference specimens from field‐collected larvae or from laboratory‐reared trap eggs, larvae, and pupae exposed in the field at 16 locations in Finland, Norway, and Sweden between 2004 and 2018 (Figure 1 , metadata S1 in Nyman et al, 2022 ). Larvae were collected when the majority had molted to their penultimate (fourth) or ultimate (fifth) instar and reared on fresh birch foliage until pupation (Ruohomäki, 1994 ).…”

“…During the study years, over 3000 adult parasitoid wasps were reared from the moth hosts in focus. The specimens to be barcoded were selected based on morphological pre‐identifications done by K. Ruohomäki mostly to the species or genus level (metadata S1 in Nyman et al, 2022 ). To evaluate intraspecific sequence variation and to facilitate detection of potential cryptic taxa within presumed species or species‐groups, we barcoded 2–23 individuals of all those morphospecies for which multiple individuals were available (metadata S1 in Nyman et al, 2022 ).…”

“…Final sample sequences were aligned with each other using the MAFFT multiple sequence alignment algorithm (Katoh & Standley, 2013 ) implemented within Geneious. We constructed two different barcode sequence alignments for the subsequent analyses: (i) an alignment including only the 132 samples analyzed in this study; and (ii) an expanded alignment including a further 66 reference sequences retrieved from the GenBank and BOLD databases (metadata S1 and data S1 in Nyman et al, 2022 ). The reference barcode sequences for the latter dataset were selected to represent (i) identified reference individuals that constituted close hits for our own barcodes; (ii) identified specimens of species that our literature review indicated as parasitoids of the focal geometrids, but that were not obtained from our own rearings; and (iii) representative congeners of parasitoids that are known to parasitize the focal moth species.…”

“… (a) Map of locations in Norway, Sweden, and Finland from which eggs, larvae, and/or pupae of Epirrita autumnata (blue dots) or both E. autumnata and Operophtera brumata (red dots) were collected for rearing of parasitoid reference specimens (see legend). Names and coordinates of the study sites are given in metadata S1 in Nyman et al ( 2022 ). (b–f) examples of larval and adult parasitoids attacking the two focal outbreaking geometrid species: (b) gregarious ectoparasitic Eulophus sp.…”