Non-lethal monitoring of longicorn beetle communities using generic pheromone lures and occupancy models

Longicorn beetles are a diverse group of insects that perform critical ecosystem services and are indicators of forest health. Most longicorn species are data deficient, and many are considered at risk. Longicorn beetle monitoring often relies on lethal methods and are time and cost intensive. In this study we investigated the use of generic pheromones in conjunction with species- and Bayesian community-level hierarchical modeling that accounts for imperfect detection, as a rapid tool for monitoring longicorn beetle diversity. Using 50 flight-intercept traps deployed for one month at two sites in a traditionally-maintained landscape in SW Romania, we implemented non-lethal surveys to evaluate the longicorn species abundance and estimate beetle occupancy. We captured and identified 2370 longicorn beetles of 28 species; two species, Phymatodes testaceus and Plagionotus detritus accounted for more than 1/2 of the captures, and nine species were only captured once. However the most abundant species estimated in our area was Mesosa nebulosa (36-60 individuals per trap location). Using co-occurrence of high and low detection species, as well as habitat associations, we estimated that 39 species (30-57 95% posterior interval) were present at any given site, suggesting that our survey did not capture the full longicorn diversity. Beetle diversity, occurrence and abundance were associated with higher tree density, volume of dead wood and number of stumps, and lower canopy cover. Our methods allowed to discriminate between common species with low detection, and rare species, and are a promising tool for the rapid assessment of longicorn beetle diversity, as well as the conservation status of listed and non-listed species.