Abstract
<jats:p>Effective prediction and management of pest outbreaks require understanding the mechanisms that synchronize populations across landscapes, yet these mechanisms are often difficult to distinguish from abundance data alone. Theory predicts that alternative synchrony mechanisms generate distinct genetic predictions that can be empirically tested. Here, we test whether genetic data can resolve competing synchrony mechanisms in the apple fruit moth ( Argyresthia conjugella), a system long interpreted as driven by trophic forcing from pulsed resources. Using a continent‑scale, multiyear dataset (1,963 individuals from 40 locations across Fennoscandia) genotyped at ten STR markers, we test four predictions expected under dispersal‑driven synchrony: low and temporally stable genetic differentiation, weak spatial structure, absence of isolation by distance, and stable genetic diversity through demographic bottlenecks. Our results are consistent with a single, well‑connected population across the region, with negligible spatial genetic structure and stable diversity despite pronounced demographic fluctuations. These findings indicate that extensive dispersal is the dominant driver of large‑scale synchrony and overrides genetic patterns expected under environmental or trophic forcing. Consequently, local pest control may have limited effectiveness, highlighting the need for coordinated regional management. More broadly, our study demonstrates the utility of population genetic data for identifying the mechanisms underlying spatial synchrony.</jats:p>