Optimizing semiochemical trap deployment for monitoring the tree-of-heaven root weevil, Eucryptorrhynchus scrobiculatus (Coleoptera: Curculionidae).

The tree-of-heaven root weevil, Eucryptorrhynchus scrobiculatus (Motschulsky) (Coleoptera: Curculionidae), is a destructive borer pest of Ailanthus altissima in China. Bottle traps baited with a vinegar-ethanol-apple (VEA) mixture have proven effective for capturing adults, but appropriate lure replacement intervals, trap spacing, and trap height for field monitoring remain to be determined. To address this, we conducted field experiments to evaluate how lure age, release distance, and deployment height influence trap efficiency. Our results revealed that VEA‑baited traps caught significantly more weevils with 2‑, 4‑, and 6‑d‑old lures compared with 8 to 24‑d‑old lures, indicating VEA retains peak attractiveness for about 6 d. Recapture rates of marked adults were highest at 1 m (30%), 3 m (33.3%), and 5 m (30%) but dropped sharply at 10 m (6.7%), 20 m (3.3%), and 30 m (5%). Trap height also had a strong effect: significantly more E. scrobiculatus were captured in traps placed at ground level (0 m) than in traps set at 5 m or 10 m. In contrast, non-target insects such as E. brandti (Harold) and Xyleborinus saxesenii Ratzeburg (both Coleoptera: Curculionidae) were more abundant at higher trap placements, demonstrating some level of vertical stratification. From independent single‑factor trials, ground‑level placement, 10‑m inter‑trap spacing and a 6‑d lure renewal interval are proposed as preliminary reference parameters for VEA‑baited trapping. These tentative indicators support field monitoring of this weevil. Our results supply evidence‑based operational guidelines for plantation managers and underpin attract‑and‑kill tactics to cut pesticide reliance and support sustainable management of A. altissima forests.