Abstract: 【Aim】 To clarify the regulatory role of apoptosis in the transmission of barley yellow dwarf virus (BYDV) GAV strain (BYDV-GAV) by Sitobion avenae. 【Methods】 The expression levels of the key apoptosis genes, including the caspase family genes Caspase-1 and Caspase-3, and the apoptosis inhibitor genes IAP-1 and IAP-2, were detected by the qPCR method, and the apoptosis levels of midgut and salivary gland tissues were also detected by TdT-mediated dUTP nick and labeling (TUNEL) assay in the BYDV-GAV-uninfected and -infected S. avenae adults. After adding the apoptosis inhibitor Ac-DEVD-CHO or the Caspase-1 specific activator PAC-1 to the artificial diet and feeding the  BYDV-GAV-infected and  -uninfected S. avencee adults, the expression levels of Caspase-1 and the copy numbers of BYDV-GAV CP in adults were examined at different virus acquisition and transmission time using the qPCR method, and the efficiency of transmitting BYDV-GAV was detected by RT-PCR. By incorporating dsRNA into artificial diets to silence Caspase-1 or IAP-1 in S. avenae adults, the silencing efficiency at different time and the corresponding effects of gene silencing on the survival and reproduction of S. avenae were determined, and the copy numbers of BYDV-GAV CP during the virus acquisition and transmission periods, and the virus transmission efficiency in S. avenae adults were also measured.【Results】Compared with the BYDV-GAV-uninfected healthy S. avenae adults, the BYDV-GAV-infected S. avenae adults showed significantly increased expression level of Caspase-1， and significantly decreased expression levels of IAP-1 and IAP-2. Additionally, the percentage of apoptotic cells in the midgut of the BYDV-GAV-infected S. avenae adults was significantly increased, as compared to that in the BYDV-GAV-uninfected healthy S. avenae adults. Compared with the control fed with dimethyl sulfoxide (DMSO), S. avenae adults fed with the activator PAC-1 exhibited enhanced expression level of Caspase-1 during the acquisition and transmission periods, and significantly decreased copy numbers of BYDV-GAV CP and the virus transmission efficiency. In S. avenae adults fed with dsCaspase-1 and dsIAP-1, the silencing efficiency of Caspase-1 and IAP-1 reached their maximum on the 3rd day (80.63% and 71.91%, respectively), as compared with that in the control fed with dsGFP. The silencing of Caspase-1 and IAP-1 had no significant effect on the survival and reproduction of S. avenae. Moreover, the copy number of BYDV-GAV CP in S. avenae adults fed with dsCaspase-1 significantly increased during the virus acquisition period as compared with that in the control fed with dsGFP. 【Conclusion】 BYDV-GAV could enhance the apoptosis level of S. avenae, which may serve as an innate immune system of S. avenae to suppress its capacity to acquire and transmit the virus. These findings provide theoretical bases for understanding the interaction mechanism between vectors and plant viruses, and a new intervention strategy to curtail the spread of plant viral diseases by targeting the apoptotic pathways in vectors.

Key words: Sitobion avenae, BYDV-GAV, apoptosis, virus transmission, gene silencing