Entomopathogenic Effects of the Plant-Associated Fungus Ochroconis guangxiensis X22 Strain on the Physiological and Metabolic State of the Rice-Pest Planthopper, Sogatella furcifera

The white-backed planthopper (Sogatella furcifera) is a major pest in rice-growing regions worldwide. It severely limits rice production through piercing–sucking feeding, oviposition injury, and by efficiently transmitting the Southern Rice Black-Streaked Dwarf Virus (SRBSDV). Previous studies demonstrated that the dark septate endophytic fungus Ochroconis guangxiensis strain X22 exhibits control activity against SRBSDV. To further evaluate its biocontrol potential, this study investigated the effects of the X22 strain on S. furcifera, the primary vector of SRBSDV. In this study, we established an X22–rice symbiotic system to evaluate its effects on the biological traits of S. furcifera. The results showed that, compared with a clear water treatment, the X22 strain significantly reduced the feeding amount (29.02%), egg-laying amount (12.30%), and hatching rate (11.58%) of S. furcifera. Gene expression analysis showed that the relative expression levels of the Target of Rapamycin (TOR) and vitellogenin (Vg) genes in one-day-old S. furcifera from the X22 treatment group were modestly downregulated, although no significant differences were detected compared with the control. Enzyme activity assays revealed that between 72 and 120 h post-treatment, the activities of detoxification enzymes, including carboxylesterase (CarE) and acetylcholinesterase (AChE), generally declined following X22 exposure. In contrast, the activities of protective enzymes, superoxide dismutase (SOD) and catalase (CAT), as well as certain digestive enzymes, α-amylase (α-AL) and trypsin, were induced. Conversely the activities of glutathione peroxidase (GSH-Px) and lipase (LPS) were suppressed. However, the physiological mechanisms underlying its effect on S. furcifera remain unclear. Collectively, these results demonstrate that the O. guangxiensis X22 strain inhibits S. furcifera reproduction by disrupting its physiological metabolism through multiple pathways, providing a mechanistic basis for its development as an environmentally friendly biocontrol agent.