Droplets matter: droplet size distribution drives the efficacy and longevity of SPLAT GM-organic formulation.

SPLAT GM-Organic, a controlled-release pheromone formulation, has been used since 2008 in an area-wide integrated pest management program targeting spongy moth, Lymantria dispar (Linnaeus) (Lepidoptera: Erebidae). In 2018, a noticeable decline in treatment performance raised concerns about potential changes in droplet characteristics affecting pheromone release and field longevity. To explore this, we evaluated the field efficacy of 3 SPLAT GM-Organic formulations applied in 2018, 2020, and 2021, and analyzed their droplet size distributions. Droplets were grouped into biologically meaningful diameter categories, and their proportions were examined using multivariate analyses and regression modeling. The findings indicate that efficacy and longevity were strongly influenced by droplet composition. Formulations containing higher proportions of large and ultra-large droplets achieved greater mating disruption and remained effective longer in the field. In contrast, formulations dominated by smaller droplets showed reduced performance. These results highlight the critical role of droplet size distribution in determining the success of SPLAT GM-Organic formulations. The ability to adjust droplet profiles through formulation design offers a practical strategy to improve the reliability and consistency of mating disruption treatments against spongy moth. More broadly, because SPLAT is widely used as a matrix for pheromone-based pest control in a variety of systems, these findings may inform formulation development and quality assurance efforts in other programs as well.