Comprehensive DNA barcode reference library and optimization of genetic divergence threshold facilitate the exploration of species diversity of green lacewings (Neuroptera: Chrysopidae)

Chrysopidae are a family of Neuroptera of significant importance in biocontrol against agricultural pests because of their predatory larvae. Currently, the taxonomy of Chrysopidae lacks a comprehensive revision, which impedes the exploration of species diversity as well as the selection and the conservation of green lacewings as biocontrol agents. We have established a DNA barcode reference library of the Chinese green lacewings based on an approximately complete sampling (95.63%) in 25 of the 34 provincial regions in China, comprising 1 119 barcodes of 25 genera and 197 species (representing 85% genera and 43.62% species from China). Combining other 1 049 high quality green lacewing DNA barcodes, we first inferred the optimal threshold of interspecific genetic divergence (1.87%) for successful species identification in multiple simulated scenarios based on present data. We further inferred the threshold of genetic divergence (7.77%) among genera with biocontrol significance. The inference and performance of the threshold appears to be mainly associated with the completeness of sampling, the proportion of closely related species, and the analytical approaches. Six new combinations, Apertochrysa platypa (Yang & Yang, 1991) comb. nov., Apertochrysa shennongana (Yang & Wang, 1990) comb. nov., Apertochrysa pictifacialis (Yang, 1988) comb. nov., Apertochrysa helana (Yang, 1993) comb. nov., Plesiochrysa rosulata (Yang & Yang, 2002) comb. nov., and Signochrysa hainana (Yang & Yang, 1991), are proposed according to integrative species delimitation. Our library and optimal threshold will effectively facilitate the exploration of species diversity of green lacewings. Our study also provides a methodological reference in molecular delimitation of other insects.