Variable resistance to spinetoram in populations of Thrips palmi across a small area unconnected to genetic similarity

The melon thrips, Thrips palmi, is an increasingly important pest of vegetables in northern China. Some populations have developed resistance in the field to the insecticide spinetoram. Understanding the origin and dispersal of insecticide-resistant populations can shed light on resistance management strategies. In this study, we tested susceptibility of seven greenhouse populations of T. palmi to spinetoram collected from a small area of about 300 km2 in Shandong province, and examined population genetic structure across the area based on a segment of mitochondrial cox1 gene and 22 microsatellite loci to infer the possible origin and dispersal of insecticide resistance. Levels of resistance to spinetoram differed among seven populations, which included one population with high resistance (LC50 = 759.34 mg/L), three populations with medium resistance (LC50 ranged from 28.69 to 34.79 mg/L) and three populations with low resistance (LC50 ranged from 7.61 to 8.97 mg/L). The populations wer..., Total DNA was extracted from individual specimens using DNeasy Blood and Tissue Kit (Qiagen, Germany). For nuclear markers, we used 22 microsatellite loci developed in a previous study (Gao, Gong, Ma, et al., 2019). A fluorescence‐labeled PC‐tail (5′ CAGGACCAGGCTACCGTG 3′) was used to label the PCR products (Schuelke, 2000; Blacket et al., 2012). Conditions for PCR amplification were described in Gao, Gong, Ma, et al. (2019). The size of amplified PCR products was determined using an ABI 3730xl DNA Analyzer with GeneScan 500 LIZ size standards. Alleles were identified with GENEMAPPER version 4.0 (Applied Biosystems, USA).

For the mitochondrial gene, a segment of cytochrome c oxidase subunit I (cox1) was amplified with primer pairs TP-AF (5′ TTTCGTCTAACCATAAAGATATCGG 3′) and TP-AR (5′TAAACTTCTGGGTGCCCAAAAAATCA 3′) (Cao et al., 2019). Polymerase chain reaction (PCR) was conducted with the following program: an initial denaturation for 3 min at 94 °C, followed by 35 cycles of 10 s at 94..., Microsatellite data (genepop format) and mitochondrial cox1 gene sequences (fasta format) for populations of Thrips palmi.

tp_22ssr_4populations_field_lab.genepop, microsatellite data for two field populations and two laboratory populations;

tp_22ssr_7populations from Shouguang.genepop, microsatellite data for seven field populations collected from Shouguang, Shandong province, China;

tp_cox1_4haps.fas, cox1 haplotypes;

tp_cox1_7populations.fas