Cloning and Preliminary Functional Studies of the Nicotinic Acetylcholine Receptor α6 Subunit in Megalurothrips usitatus (Bagnall)

To investigate the functional role of the nicotinic acetylcholine receptor (nAChR) α6 subunit in Megalurothrips usitatus and its involvement in insecticide resistance, we cloned the nAChR α6 gene (Muα6) using RACE technology and analyzed its spatiotemporal expression patterns via RT-qPCR. Functional studies were further conducted under spinetoram stress. The results showed that Muα6 (GenBank accession: PQ441948) has a full-length sequence of 1569 bp, encoding 523 amino acids with four transmembrane domains (TM1-TM4), six extracellular loops (Loop A-F), and two N-glycosylation sites (Asn100 and Asn144). Multiple sequence alignment revealed 95.53% similarity between Muα6 and the α6 subunit of Frankliniella occidentalis (AOT81842.1). Alternative splicing analysis identified four isoforms (3a8a/3a8b/3b8a/3b8b), with 3b8a being the dominant type (58.3%). Spatiotemporal expression profiling demonstrated the highest Muα6 expression in pupae and the lowest in second-instar nymphs. In adults, Muα6 expression in the abdomen was significantly lower than in the head and thorax. After 48 h exposure to spinetoram (LC₅₀ = 1.243 mg·L⁻¹), Muα6 expression was significantly upregulated to 2.05-fold the control level (p < 0.05). This study is the first to elucidate the molecular characteristics and expression regulation of the Muα6 in M. usitatus. The insecticide-induced upregulation suggests its potential role in target-site resistance, providing a theoretical basis for understanding the mode of action of spinosyns and guiding field resistance management strategies.