Roles of the chemosensory protein <i>RpCSP8</i> in reproduction and feeding behavior of sexual and non‐sexual female of <i>Rhopalosiphum padi</i>

Chemosensory proteins (CSPs) are small soluble proteins that play various roles in insects. The non-sexual parthenogenetic females (virginoparae) of Rhopalosiphum padi can transition to sexual reproduction and produce sexual females (oviparae) when exposed to short photoperiods and low temperatures. To date, research on the distinct roles of chemosensory proteins in sexual versus parthenogenetic female aphids remains scarce. In this study, we investigated the roles of RpCSP8 in R. padi. Among the eight RpCSPs, RpCSP8 exhibited a 3.81 fold higher expression in the oviparae compared to virginoparae. Across developmental stages and tissues, RpCSP8 showed the highest expression in the fourth-instar nymphs and adults, as well as in the salivary glands of oviparae. In contrast, it exhibited the highest expression in adults and the antennae of virginoparae. In oviparae, knockdown of RpCSP8 significantly impaired reproductive performance: fecundity decreased by over 80%, and lifespan was reduced by more than 50%. RpVg (vitellogenin) expression declined by 37.1%, although no significant differences in egg morphology were detected. Electrical penetration graph (EPG) recordings revealed that RpCSP8 knockdown in oviparae significantly reduced phloem ingestion duration, indicating impaired feeding behavior. In virginoparae, knockdown of RpCSP8 showed no significant changes in fecundity, lifespan, or feeding behavior. These results demonstrate different roles for RpCSP8 in regulating both reproductive output and host plant utilization in the oviparae and virginoparae of R. padi. This study reveals the non-chemosensory functions of insect CSP and provides new insights into the adaptive mechanisms underlying reproductive mode transitions and host switching in R. padi.