Preparation of databases of DNA barcodes
Sequences of the 375 individuals collected during our field sampling were queried in BOLD search engine (Ratnasingham & Hebert 2007) to double-check the species identity in those specimens previously determined according to morphology. We used the option All Barcode Records in BOLD, as all our sequences were longer than 500bp and doing so the query sequences are compared with a larger number of reference barcodes. Besides, we mined BOLD searching for COI DNA barcodes of the same species that we had sequenced in the Iberian Peninsula; in total we could download 277 public sequences (available in January 2018), which were used in further analyses (see Supplementary material section for BOLD process IDs).
The final database pooling the sequences downloaded from BOLD with the new Iberian sequences added up to 652 COI barcodes: 21 taxa from 136 localities in 14 European countries (Fig. 1). For the data downloaded from BOLD, we considered two sequences to come from the same locality when the name for that field site was identical in the database or when the coordinates showed that the specimens had been collected within a distance lower than 5 kilometres. We chose this threshold because, given that these species of oak feeding moths are not migratory and have limited dispersal abilities (Ruíz-Carbayo et al. 2017), individuals within this range may belong to the same population.