# Decoding Biodiversity in Baiyangdian Lake: A DNA Barcode Reference Library for Aquatic Insects

## TL;DR

This study created a DNA barcode library for aquatic insects in Baiyangdian Lake to help monitor biodiversity and support conservation efforts.

## Contribution

The first comprehensive DNA barcode reference library for aquatic insects in Baiyangdian Lake is developed using COI gene sequencing.

## Key findings

- DNA barcoding using the COI gene successfully distinguished all species in the study.
- Diptera, especially Chironomidae, showed the highest diversity in Baiyangdian Lake.
- The barcode library captures most genus-level diversity but reveals incomplete species-level diversity, particularly among Diptera.

## Abstract

Freshwater ecosystems are highly threatened, and reliable biodiversity monitoring is vital for their protection. Baiyangdian Lake, the largest freshwater lake in northern China, has suffered severe degradation but is now being restored. To support these efforts, we created a DNA barcode reference library of aquatic insects using the COI gene. Between 2023 and 2025, we collected samples from different habitats and generated 315 DNA sequences representing more than 100 species. The results showed rich insect diversity, with midges and dragonflies as dominant groups, and confirmed that DNA barcoding can clearly distinguish all species. This study provides the first comprehensive genetic reference for Baiyangdian aquatic insects. It will help track biodiversity recovery, guide conservation strategies, and supply valuable data for global databases, offering an efficient tool to evaluate ecological restoration and protect freshwater ecosystems.

Freshwater ecosystems are among the most vulnerable habitats worldwide, and reliable biodiversity assessment is essential for their conservation. Baiyangdian Lake, the largest freshwater lake in northern China, has undergone severe ecological degradation but is now experiencing recovery through restoration efforts. To provide a molecular basis for monitoring biodiversity, we constructed a COI DNA barcode reference library of aquatic insects from Baiyangdian Lake. From January 2023 to May 2025, systematic sampling across representative habitats yielded 315 high-quality sequences covering 104 species, 74 genera, and 33 families within eight insect orders. Diptera, particularly Chironomidae, showed the highest diversity, followed by Odonata. Phylogenetic analysis using maximum likelihood resolved all orders and families as well-supported monophyletic groups, demonstrating strong congruence with morphological taxonomy. Genetic distance analysis revealed a pronounced barcode gap, with mean intraspecific divergence of 0.46% and nearest-neighbor divergence exceeding 15%, confirming the discriminatory power of COI for species identification. Accumulation curves indicated that genus-level diversity is largely captured, while species-level diversity, especially among Diptera, remains incompletely revealed. This study provides the first comprehensive DNA barcode reference library for Baiyangdian aquatic insects, supporting ecological restoration evaluation, eDNA applications, and regional biodiversity conservation strategies.