BIOTYPES OF THE CASTOR BEAN WHITEFLY TRIALEURODES RICINI (MISRA) (HOM., ALEYRODIDAE) IN EGYPT - BIOCHEMICAL-CHARACTERIZATION AND EFFICIENCYOF GEMINIVIRUS TRANSMISSION

The newly introduced castor bean whitefly (CBW) Trialeurodes ricini (M isra) has become an important pest which is widely spread all over Egy pt. 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. ri cini adults were collected from castor bean (Ricinus communis) at diff erent geographical locations representing the Egyptian Delta and Nile valley governorates. Esterase banding patterns were investigated to ev aluate the extent of variation among the tested populations of the cas tor bean whitefly. Electrophoresis of homogenates of individual T. ric ini females showed that there are five different biotypes (C-1-C-5). T he predominant biotype (C-1 type) was found in about 80% of the tested locations. In transmission studies, the polymerase chain reaction (PC R) was used to detect geminiviruses in nucleic acid extracted from the different castor bean whitefly biotypes. PCR revealed that the five b iotypes of T. ricini are viruliferous. To evaluate the efficiency of t he predominant T. ricini biotype for transmitting the tomato yellow le af curl virus (TYLCV), acquisition and inoculation access periods were determined. PCR indicated that 50% of whitefly adults collected from castor bean, acquired the virus after 10 h exposure to TYLCV infected tomato. Experimentally, the rate of transmission increased as the inoc ulation access period was lengthened and reached a maximum after 4 h. The obtained symptomatological results were also confirmed by PCR.