Classification, identification, and DNA barcoding study for common cockroach species (Dictyoptera: Blattaria) from China

Cockroaches are well-known pests and quarantined organisms worldwide. Due to morphological diversity and a lack of molecular data, their classification and identification are facing challenges. This study performed classification, identification, and DNA barcoding for cockroaches collected from China. Seventy-six samples were morphologically identified as seven species of two superfamilies that included Blattella germanica, Eublaberus posticus and Blaptica dubia belonging to the superfamily Blaberoidea, and Periplaneta americana, Periplaneta lateralis, Periplaneta fuliginosa and Periplaneta australasiae belonging to the superfamily Blattoidea. Based on sequence alignments of nine ribosomal and mitochondrial genes across the order Blattaria retrieved from GenBank, rDNA ITS2-517 bp and mtDNA 16S-327 bp were screened as candidates for molecular identification. Universal primers were designed for PCR amplification, cloning, and sequencing of the 37 representative samples. Sequence alignments and phylogeny analysis showed that both ITS2 and 16S confirmed samples 1–9, 20–24, and 25–29 as B. germanica, P. americana, and P. lateralis, respectively; only 16S (not ITS2) confirmed samples 10–14, 15–19, 30–34, and 35–37 as E. posticus, Blap. dubia, P. fuliginosa, and P. australasiae, respectively, indicating that 16S was a better target than ITS2 for molecular identification of cockroaches. Conservative motif and divergence analysis further revealed that ITS2 sequences vary significantly among different taxa, whereas 16S sequences are relatively conserved. There is an obvious barcoding gap between maximum intraspecific divergence and minimum interspecific divergence (2.57 % vs. 5.62 %) for ITS2, but not for 16S (6.15 % vs. 2.63 %). Therefore, it was confirmed that ITS2 is an ideal DNA barcode for molecular identification of cockroaches at lower category.