| Summary: | Insects harbor a wide variety of symbiotic microorganisms that are capable of regulating host health and promoting host adaptation to their environment and food sources. However, there is little knowledge concerning the mechanisms that maintain the microbial community homeostasis within insects. In this study, we found that the <i>intersex</i> (<i>ix</i>) gene played an essential role in maintaining microbial homeostasis in the brown planthopper (BPH), <i>Nilaparvata lugens</i>. Injection of the double-strand RNA targeting <i>N. lugens ix</i> (<i>Nlix</i>) into the newly emerged females resulted in abnormal expansion of the copulatory bursa of BPH after mating. Further observation by transmission electron microscopy (TEM) revealed that the abnormally enlarged copulatory bursa resulting from ds<i>Nlix</i> treatment was full of microorganisms, while in contrast, the copulatory bursa of ds<i>GFP</i>-treated individuals stored a large number of sperm accompanied by a few bacteria. Moreover, RNA-seq analysis showed that the gene responses to bacteria were remarkably enriched in differentially expressed genes (DEGs). In addition, 16s rRNA sequencing indicated that, compared with control samples, changes in the composition of microbes presented in ds<i>Nlix</i>-treated copulatory bursa. Together, our results revealed the immune functions of the <i>Nlix</i> gene in maintaining microbial homeostasis and combating infection in BPH.
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