Evaluation of vinegar effectiveness in carabid traps (Coleoptera: Carabidae): A viable alternative to conventional liquids

In response to the growing challenges of sustainable agriculture and the preservation of functional biodiversity, robust entomological monitoring protocols now require large-scale sampling, leading to significant operational costs. In this context, the adoption of cost-effective alternatives to preservation liquids is crucial. Vinegar, propylene glycol, and brine are three solutions commonly used in the literature, raising questions regarding the comparability of data across studies. We compared the effectiveness of vinegar, propylene glycol, and brine in Barber traps for the census of carabids (Carabidae), key auxiliaries in agroecosystems. Trapping campaigns were conducted in 2023 across 20 sugar beet plots (vinegar vs. propylene glycol) and in 2024 across 17 winter cereal plots (vinegar vs. brine), following standardized protocols. The results indicate that traps containing vinegar captured significantly more individuals overall than the other liquids, while maintaining a comparable species diversity and assemblage composition to those obtained with propylene glycol. In contrast, brine showed more variable captures compared to the other liquids and should be excluded for more reliable surveys. These findings suggest that vinegar, as an economical option, represents a promising alternative to propylene glycol for carabid census. However, the choice of preservation liquid should align with the specific objectives of each study: propylene glycol remains preferable for specimen preservation, particularly for DNA analyses, while vinegar offers an affordable solution for studies not requiring such analyses.