Rapid development of broad regional and international DNA barcode libraries have brought new insights into the species diversity of many areas and groups. Many new species, even within well-investigated species groups, have been discovered based initially on differences in DNA barcodes. We barcoded 437 collection specimens belonging to 40 pre-identified Palearctic species of the Elachista bifasciella group of moths (Lepidoptera, Elachistidae). Although the study group has been a subject of several careful morphological taxonomic examinations, an unexpectedly high number of previously undetected putative species is revealed, resulting in a 34% rise in species number in the study area. The validity of putative new species was subsequently supported with diagnostic morphological traits. We show that DNA barcodes provide a powerful method of detecting potential new species even in taxonomic groups and geographic areas that have previously been under considerable morphological taxonomic scrutiny.

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Morphological traits characterizing and delimiting Pleurotinae (Oecophoridae) are provided and discussed. The evidence supports the validity of the subfamily as suggested by recent molecular studies. The Pleurota aristella (Linnaeus, 1767) species group is characterized, and six new species belonging to the group from Morocco are described: Pleurota tricolor Tabell, sp. nov., P. pellicolor Tabell, sp. nov., P. lacteella Tabell, sp. nov., P. moroccoensis Tabell, sp. nov., P. ochreopalpella Tabell, sp. nov., and P. atlasensis Tabell, sp. nov. Habitus images and label data are provided for the types of P. goundafella Zerny, 1935; P. insignella Zerny, 1935; P. ochreostrigella Baker, 1885; P. macrosella Rebel, 1900; P. staintoniella Baker, 1888; P. mauretanica Baker, 1888; and P. algeriella Baker, 1885. DNA barcodes of the new species are compared with all available Pleurotinae sequences (BIN n = 117) in BOLD.

We studied 105 genitalia of mostly Finnish male Coleophora vacciniella Herrich-Schäffer, 1861, in order to inspect the variation in certain features: the number of chitinous teeth on the dorsal side of the phallotheca, the number of spines at the distal end of it, and the number of cornuti in the vesica. All of the parameters were close to a normal distribution, which did not coincide with our original idea of splitting this species complex into two or even more species. On the contrary, we had to synonymise C. betulaenanae Klimesh, 1958, with C. vacciniella, as we could not find reasonable differences between them.

Elachista (Elachista) deriventa Kaila & Mutanen sp. n. is described on the basis of specimens collected in southern Finland. The new species inhabits shady forests and Calamagrostis arundinacea is recorded as its host plant. The species is closest to E. elegans Frey, but differs from that by details in morphology and life history. Diagnostic characters and illustrations are provided for close relatives.