A pheromone-based toolbox of longhorn beetles (Cerambycidae) for monitoring biodiversity in ephemeral deadwood substrates of oak

Forest biodiversity is exhibiting a worldwide decline in response to environmental changes that result in the rapid loss, degradation, and fragmentation of essential forest habitats. Saproxylic insects, especially beetles, are an important part of forest biodiversity by contributing to deadwood decomposition, and serving as important components of food webs. Many saproxylic beetles display negative population trends, and are listed on national and European Red Lists of threatened species. Despite their great importance, present knowledge on the ecology and conservation requirements of these beetles is limited, in part due to the absence of efficient tools to sample populations of many species. Recently, pheromone-based methods have been proposed as a novel tool to study saproxylic insects. Unfortunately, thus far, pheromones have only been identified for a small number of species of interest to conservation. In this work I identified the aggregation-sex pheromones of longhorn beetles dependent on fresh, recently dead, wood substrates of oak in Sweden, and examined the usefulness of the pheromone-based trapping approach for detecting local populations, and studying the species’ ecology. The pheromone-chemistry of eight species was considered, with a total of seven identified pheromone compounds (hydroxyketones, alcohols, and one ketone). The pheromones were used for systematic, large-scale monitoring studies in southern Sweden. The results served to significantly change the perception of several species’ distribution and abundance. Further, local beetle abundance (trap captures), was best correlated with habitat at relatively large spatial scales, indicating that future detailed analyses of the species’ ecology need to consider large spatial scales. Effects of oak forest management and habitat structure were examined in a three-year monitoring study. Generally, beetle abundance did not differ between ordinary oak production stands and two types of set-aside habitats for biodiversity. Most species also preferred more open, sun-exposed oak habitats. In addition, the beetles displayed short-term positive responses to logging in oak production stands, when fresh oak substrates were retained on site. The work clearly demonstrated the advantages of using pheromones to study these species and also offered early insights into the complicated, and highly dynamic, ecology of the species.