BEER, WINE, OR FRUIT JUICE: WHICH IS BEST? A CASE STUDY OF BAIT EFFICIENCY TO SAMPLE SAPROXYLIC BEETLES (COLEOPTERA) IN AN OAK WOODLAND

Aerial traps composed of plastic water bottles baited with attractive liquids are often used to inventory beetles, especially longhorns (Cerambycidae) and flower beetles (Scarabaeidae: Cetoniinae). Many different bait mixtures exist but their effectiveness has rarely been scientifically tested. Six different mixtures, involving red wine, white wine, lager beer, apple juice, and vinegar, as well as a water and sugar control, were compared. Fourteen replicates of the seven attractants were arranged in a thermophilic oak forest in the southwest of France. In terms of abundance and richness per trap, two attractants proved to be significantly less effective: The control and the juice mixture. The other five are equivalent for richness. For flower beetles, red wine + white wine and beer + sugar mixtures collected significantly more individuals. However, the sample collected by the beer + sugar mixture showed a lower diversity than the other wine + beer mixtures, due to the dominance of a few species of flower beetles. In terms of species composition, there was no qualitative difference between the attractants. Taking abundance into account (Bray-Curtis index), the beer + sugar blend differed from the others due to the high abundance of Cetonia aurata (Linnaeus, 1758). This study provides reasonable confidence that inventories conducted with different baits based on red wine or beer return comparable results. Finally, we recommend the beer + red wine mixture, which presents a good compromise between abundance and diversity for the different families, and is already frequently used.