Inreasing damage of pests in agriculture and forestry can arise both as a consequence of changes in local species and through the introduction of alien species. In this study, we used population genetics approaches to examine population processes of two pests of the tree-of-heaven trunk weevil (TTW), Eucryptorrhynchus brandti (Harold) and the tree-of-heaven root weevil (TRW), E. scrobiculatus (Motschulsky) on the tree-of-heaven across their native range of China. We analyzed the population genetics of the two weevils based on ten highly polymorphic microsatellite markers. Population genetic diversity analysis showed strong population differentiation among populations of each species, with FST ranges from 0.0197 to 0.6650 and from -0.0724 to 0.6845, respectively. Populations from the same geographical areas can be divided into different genetic clusters, and the same genetic cluster contained populations from different geographical populations, pointing to dispersal of the weevils possibly being human-mediated. Redundancy analysis showed that the independent effects of environment and geography could account for 93.94% and 29.70% of the explained genetic variance in TTW, and 41.90% and 55.73% of the explained genetic variance in TRW, respectively, indicating possible impacts of local climates on population genetic differentiation. Our study helps to uncover population genetic processes of these local pest species with relevance to control methods.

We collected 13 TTW and 11 TRW populations across their native range of China (Table 1, Figure 1). The two weevils are the primary pests of the tree-of-heaven, and we sampled sites separated by variable distances (30-2100 km). To avoid the collection of siblings, one adult individual was collected from each tree. The samples were kept in 100% ethanol and stored at -80°C before DNA extraction. Total genomic DNA was extracted from the legs of each adult using the DNeasy Blood & Tissue Kit (Qiagen, Hilden, Germany) according to the manufacturer's instructions.

Ten microsatellite loci from Zhang et al. (2021) were used in our study (Table S1) and genotyped using the same methods. The size of amplified PCR products was determined using an ABI 3730xl DNA Analyzer with GeneScan 500 LIZ size standard. Alleles were identified with GENEMAPPER v 4.0 (Applied Biosystems, USA).

Microsatellite data in genepop format for Eucryptorrhynchus brandti (Harold) (TTW) and E. scrobiculatus (Motschulsky) (TRW).