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The mirid bug Cyrtorhinus lividipennis (Reuter) is an important predator that consumes eggs and young nymphs of the brown planthopper Nilaparvata lugens as a primary food source and thus becomes an important member of the rice ecosystem. We identified and characterized the ClPSP gene in C. lividipennis encoding the phosphoserine phosphatase enzyme. The ClPSP has an open reading frame (ORF) of 957 bp encoding a protein with a length of 294bp and it possesses a haloacid dehalogenase-like (HAD) hydrolase, phosphoserine phosphatase, eukaryotic-like (HAD_PSP_eu) conserved domain. Furthermore, the in silico analysis of the ClPSP gene unveiled its distinct characteristics and it serves as a key player in the modulation of amino acids. The ClPSP showed expression in all developmental stages, with higher expression observed in the ovary and fat body. Silencing the ClPSP by RNA interference (RNAi) significantly decreased PSP enzyme activity and expression compared to dsGFP at two days after emergence (2DAE). The dsPSP treatment altered free hemolymph amino acid compositions, resulting in a significant reduction of serine (Ser) and Arginine (Arg) proportions and a significant increase of Threonine (Thr), Cystine (Cys), and Tyrosine (Tyr) in the C. lividipennis female at 2 DAE. Additionally, a hindered total protein concentration in the ovary and fat body, and reduced vitellogenin (Vg) expression, body weight, and number of laid eggs, were also observed. The same treatment also prolonged the preoviposition period and hindered ovarian development. Our data, for the first time, demonstrated the influential role of the PSP gene in modulating the fecundity of C. lividipennis and provide a platform for future insect pest control programs using the PSP gene in modulating fecundity. [ABSTRACT FROM AUTHOR]