Field assessment of synthetic attractants and traps for the cerambycid beetles Tetropium castaneum L. and Tetropium fuscum (F.) in the Eastern Carpathians, Romania

Tetropium species, significant forest pests in some countries, are expected to pose an even more significant threat in the context of climate change and biological invasions. The potential impact is substantial, making detecting their presence and monitoring their populations crucial. The research presented in the paper aimed to test the response of adults of Tetropium castaneum (Linnaeus,1758) and Tetropium fuscum (Fabricius, 1787) to synthetic attractants similar to those used in other countries (two experiments) and to verify the effectiveness of three types of traps in their capture (one experiment). The experiments were conducted in six freshly clear-cutting areas located in spruce or mixed stands in the northern part of the Eastern Carpathians. In the first two experiments, carried out between 2015 and 2016, we investigated the response to fuscumol, both alone and in combination with host tree volatiles (monoterpenes and ethanol) released at different rates. We also tested a combination of (-)-alpha-pinene, ethanol, and aggregative pheromone of Ips typographus (C.Linnaues, 1758). Barrier traps were used in these initial experiments. The third experiment, conducted in 2017, evaluated the effectiveness of Crosstrap, Barrier, and MultiWit traps, all baited with lures of fuscumol, (-)-alpha-pinene, and ethanol. Numerous specimens of both species were caught in all experiments, namely 7,824-10,466 T. castaneum and 1,041-1,215 T. fuscum. The sex ratio (M/F) varied from 1:1.02 to 1.36:1 for the first species and from 1:1.03 to 1.55:1 for the second. All the baits tested were found to be significantly attractive to the adults of both species. The differences in average catches recorded in traps baited with fuscumol or combinations of attractants were statistically significant compared to those in unbaited traps. Additionally, the catches from traps baited with fuscumol and host volatiles differed significantly from those baited with fuscumol alone. However, there were no significant differences in the average catches of traps baited only with fuscumol compared to those baited with (-)-alpha-pinene, ethanol, and synthetic I. typographus pheromone. Baits containing fuscumol primarily attracted female insects, but when baits with host volatiles were added to those containing fuscumol, the proportion of males in the total catches increased. The Crosstrap and Barrier traps captured significantly more specimens of T. castaneum and T. fuscum than the MultiWit traps, with capture rates 3.20 to 5.57 times higher for T. castaneum and 4.81 to 8.56 times higher for T. fuscum. However, the differences between the Crosstrap and Barrier traps were not statistically significant. Fuscumol baits, whether used independently or alongside host tree volatiles, demonstrate significant attractiveness to beetles of both Tetropium species in Romania. Adding monoterpenes and ethanol lures creates a powerful synergistic effect, remarkably enhancing the allure of fuscumol, particularly for T. fuscum compared to T. castaneum. Moreover, a combination of (-)-alpha-pinene, ethanol, and aggregative pheromone of Ips typographus matches the attractiveness of fuscumol lures, making it an effective alternative. For effective detection and monitoring of Tetropium native or exotic species, fuscumol lures in conjunction with host volatile baits and Crosstrap or Barrier traps are recommended. This approach improves population monitoring and ensures reliable results.