Optimisation of an effective trapping system for monitoring fall armyworm <i>Spodoptera frugiperda</i> : lure composition, dosage, trap design, and nonanal synergist

The invasive fall armyworm, Spodoptera frugiperda (Smith JE) (Lepidoptera: Noctuidae) is a major invasive agricultural pest worldwide, requiring effective monitoring tools for timely integrated pest management (IPM). The efficacy of pheromone lures can vary geographically, necessitating regional validation and optimisation. To develop a regionally optimised trapping system for monitoring S. frugiperda populations in Zhejiang Province, China, we conducted sequential two-year field trials to evaluate the effects of seven sex pheromone blends, five lure dosages, four trap designs, and the potential synergist nonanal on trapping efficiency. Our results demonstrated that a two-component blend of (Z)-9-tetradecenyl acetate and (Z)-7-dodecenyl acetate in a 99.4:0.6 ratio was the most attractive and specific lure. Trap captures were highest with a high dosage (3,000 µg) deployed in a bucket trap, which significantly outperformed delta, wing, and vertical traps. The addition of 120 µg nonanal to the two-component blend acted as a synergist, significantly increasing S. frugiperda captures. The optimised system was then applied to monitor the local seasonal population dynamics of S. frugiperda, revealing a main flight peak in late September. This study provides the first optimised trapping system for S. frugiperda in this key agricultural region, offering a validated tool for precise, data-driven monitoring and defining a clear 'action window' for improving the sustainable management of this invasive pest.