Evaluating DNA quality in Coleoptera and Lepidoptera: impact of fixation and preservation in various trapping methods

Despite advancements in barcoding and metabarcoding, preserving high-quality DNA from field-collected arthropods remains challenging. While various fixatives and preservatives are used for DNA recovery in Coleoptera and Lepidoptera, their effects on DNA quality across different trapping methods are not fully understood. This study evaluates fixation and preservation strategies affecting DNA integrity, focusing on pH changes before and after tissue grinding to improve consistency.

For Coleoptera (Carabidae), Calathus fuscipes (L.) specimens were collected using Malaise trap, while Platynus assimilis (Paykull) were collected using emergence trap and pitfall traps (with and without roof), with propylene glycol as the primary fixative. Preservation methods included propylene glycol, 96% ethanol, or drying, with samples stored at –20 °C for one year. Propylene glycol-stored samples were washed with distilled water prior to grinding. Individual trapping used additional fixatives, including ethylene glycol, ethanol, brine, ethyl acetate, vinegar, and drying (with and without silica gel), stored at –20 °C for three months.

For Lepidoptera, samples were categorized by size: large–Agrostis exclamationis (L.), medium–Meganola strigula (Denis et Schiffermüller), Eupithecia insigniata (Hübner), and small–Pelochrista caecimaculana (Hübner). Specimens were treated with chloroform (vapor and soaked) or cyanide vapors and stored at room temperature for three months.

DNA quality was assessed through gDNA fragmentation and PCR amplification of COI fragments (658, 313, 157 bp for Coleoptera and 658, 311, 220 bp for Lepidoptera) with Sanger sequencing.

Results showed reduced DNA integrity in diluted Malaise trap samples, while distilled water washing enhanced DNA readability for emergence trap with propylene glycol. Brine proved to be a cost-effective preservative for individual trapping. For Lepidoptera, DNA preservation depended on sample size and fixative, with small chloroform-soaked specimens yielding non-sequencable DNA, while vapor-treated samples remained sequencable. This study provides insights for optimizing DNA yield and establishing effective preservation protocols for arthropod genetic research.