TRANSMISSION OF TOMATO YELLOW LEAF CURL GEMINIVIRUS BY BEMISIA-TABACI(HOMOPTERA, ALEYRODIDAE)

The sweetpotato whitefly, Bemisie tebaci (Gennadius), is an economical ly important pest worldwide. A new biotype of sweetpotato whitefly, bi otype B, causes extensive damage by direct feeding and by the transmis sion of plant viruses, such as geminiviruses. Because of the importanc e of whitefly-transmitted geminiviruses, studies were conducted to qua ntify the characteristics of tomato yellow leaf curl geminivirus (TYLC V) transmission by the vector B. tabaci. Transmission of an isolate of TYLCV from Egypt was achieved with one adult B. tabaci per plant, but the efficiency of transmission increased fourfold when the number of adults were increased to five per plant. B. tabaci transmitted TYLCV a fter a minimum acquisition-access period of 15 min, and rate of transm ission increased as the acquisition-access period was lengthened and r eached a maximum after 24 h. A minimum inoculation-access period of 15 min was observed with the rate of transmission increasing as the inoc ulation-access period was lengthened, reaching a maximum after a 12-h inoculation-access period. When B. tabaci were transferred serially af ter acquisition, adults were unable to transmit TYLCV until 24 h after the initiation of the acquisition-access period regardless of the len gth of acquisition provided. The 24-h transmission threshold from init ial vector access to a TYLCV-infected plant until transmission of the virus includes both the acquisition-access period and the latent perio d during which the virus circulates within the vector. Retention of TY LCV from the nymphal to adult stages of B. tabaci was supportive of a circulative mode of transmission. TYLCV titer in B. tabaci after an ac quisition-access period of 12 h continuously increased on a non-TYLCV host starting at 12 h, reaching a peak at 108 h and remaining stable f rom 132 to 180 h after the acquisition-access period. These data indic ate multiplication of the virus in the vector as the most likely expla nation for the continuous increase of TYLCV titer.