Plant-Derived BtHCYP Promotes Phloem Feeding and Fecundity in Bemisia tabaci

Bemisia tabaci is a destructive agricultural pest with a remarkable capacity to exploit diverse host plants. Horizontally transferred genes (HTGs) have recently been implicated in this adaptive success, yet the functions of most HTGs in the whitefly remain unclear. Feeding behavior is crucial for nutrient acquisition and reproduction in piercing-sucking insects, but whether HTGs contribute to host adaptation by regulating feeding remains largely unknown. Here, we identified BtHCYP, a plant-derived HGT gene in B. tabaci encoding a cysteine protease. Biochemical and in vivo assays confirmed that BtHCYP retained cysteine protease activity. RNA interference-mediated silencing of BtHCYP significantly reduced whitefly fecundity. Electrical penetration graph on cotton plants analyses further revealed that BtHCYP knockdown impaired phloem feeding. Collectively, these findings demonstrate that a plant-derived HTG can enhance whitefly fecundity and efficient phloem feeding, as BtHCYP silencing reduced oviposition by 27.6%, highlighting a potential molecular target for whitefly management.