The shape and material of the flight interception trap matter for beetle sampling

Beetles are one of the most diverse insect groups, playing vital roles in ecosystem functions such as decomposition and pollination. Despite their ecological importance, their immense diversity is often undersampled due to inconsistent and non-standardised sampling methodologies. We assessed the sampling efficiency of flight interception traps using six trap designs that differed in shape and panel material in a hemiboreal, mixed deciduous forest. We compared the designs in terms of species number, abundance, diversity of beetles, and saproxylic beetle species. Trap efficiency was evaluated using species accumulation curves. We collected a total of 457 beetle species (8,552 individuals) from 51 families, including 272 saproxylic species. Although species accumulation curves showed signs of flattening, significant differences were observed among trap designs. Panels made of soft plastic (polyethylene) outperformed those made of hard plastic (polycarbonate) in terms of species diversity and the proportion of red-listed species captured. No differences in body size were detected among the trap catches. Our results highlight an overlooked yet significant effect of panel material in sampling beetle communities. The combination of soft plastic panels with a triangular trap design significantly improved trap efficiency. This improvement not only enhanced the capture of common beetle species but also resulted in a higher sampling rate of those of conservation concern. These findings underscore the importance of selecting appropriate trap designs to increase the accuracy of biodiversity assessments to make better-informed conservation decisions. A standardised trap design would enhance comparability across studies, improving ecological inferences.