Small-scale dispersal and gene flow of the agricultural pest two-spotted spider mite in apple orchards: Implication from landscape ecological and population genetic analyses

The two-spotted spider mite, Tetranychus urticae Koch (Acarina, Tetranychidae), is a notorious agricultural pest known for its high dispersal ability. Understanding the dispersal patterns of T. urticae is crucial for studying its population dynamics and assessing the risk of gene dispersal related to acaricide resistance. We investigated the impact of surrounding landscapes on T. urticae occurrence and detected gene flow between nearby apple orchards. Land use data within 0.2–2 km radius buffers of the orchards were extracted and summarized using principal component analysis. The effects of landscape composition on the occurrence of T. urticae in apple orchards were analyzed using a hierarchical Bayesian model that considers spatial autocorrelation. In addition, we conducted a population genetic analysis on samples collected from five orchards. The results indicate that the best model was one at a 200-m scale, revealing a positive correlation between forest area ratio and T. urticae occurrence. The population genetic analysis demonstrated distinct genetic structures within T. urticae populations across different orchards. However, we estimated gene flow among some orchards that were geographically close. These findings suggest that T. urticae may migrate from surrounding landscapes, particularly forests, and nearby orchards to apple orchards. These findings have substantial implications for developing control units based on the gene flow range of the two-spotted spider mite, as well as for assessing the risk of infestation in each orchard.