Biotypes of the castor bean whitefly Trialeurodes ricini (Misra) (Hom., Aleyrodidae) in Egypt: biochemical characterization and efficiency of geminivirus transmission.
The newly introduced aleyrodid Trialeurodes ricini has become an important pest which is widely spread all over Egypt. Biochemical studies were conducted to distinguish the different T. ricini biotypes and to determine the biotype economic threshold based on its ability to transmit plant viruses. Forty-five samples of T. ricini adults were collected from castor bean (Ricinus communis) at different geographical locations representing the Egyptian Delta and Nile valley governorates. Esterase banding patterns were investigated to evaluate the extent of variation among the tested populations of T. ricini. Electrophoresis of homogenates of individual T. ricini females showed that there were five different biotypes (C1-C5). The predominant biotype (C1 type) was found in about 80% of the tested locations. In transmission studies, the polymerase chain reaction (PCR) was used to detect geminiviruses in nucleic acid extracted from the different biotypes. PCR revealed that the five biotypes of T. ricini are viruliferous. To evaluate the efficiency of the predominant T. ricini biotype for transmitting tomato yellow leaf curl bigeminivirus (TYLCV), acquisition and inoculation access periods were determined. PCR indicated that 50% of adults collected from castor bean acquired the virus after 10 h exposure to TYLCV-infected tomato. Experimentally, the rate of transmission increased as the inoculation access period was lengthened, and reached a maximum after 4 h. These results were also confirmed by PCR.