High utility of DNA barcoding for species identification and cryptic diversity in Korean aphids (Hemiptera: Aphididae)

Aphids (family Aphididae) are among the most species-rich groups of Sternorrhyncha in the order Hemiptera, and have a complex life cycle that can include several different phenotypes that are perfectly adapted to specific ecological niches. However, because aphids have a small body size, indistinct appearance, and cryptic adult behavior, their species level identification is often difficult and may be time-consuming. To overcome these limitations, DNA barcoding has been employed as an effective tool for species identification. In this study, we conducted a DNA barcoding test based on 566 specimens of Korean Aphididae, representing 125 morphospecies. Based on intraspecific genetic divergence, a threshold of 2% was estimated to efficiently differentiate the morphospecies. Only 87 morphospecies (69.6%) identified across four species delimitation methods (namely, automatic barcode gap discovery, assemble species by automatic partitioning, Poisson-tree-processes or PTP, and Bayesian implementation of the PTP) were consistent with the morphological identifications of the species. This indicates the presence of many cases of cryptic diversity among the other morphospecies, except the abovementioned 87 species. Careful morphological examination of morphospecies exceeding 2.0% intraspecific variability revealed cryptic diversity in three species (Eriosoma yangi, Tuberculatus kuricola, and Greenidea kuwanai). Two morphospecies, Sitobion avenae and Aphis craccivora, also exhibited high intraspecific divergence and comprised a single molecular operational taxonomic unit. Overall, our findings indicate that DNA barcoding can be a powerful tool for identifying species belonging to the family Aphididae, while also revealing cases of cryptic diversity.