Biotypes of the castor bean whitefly Trialeurodes ricini (Misra) (Hom., Aleyrodidae) in Egypt: Biochemical characterization and efficiency of geminivirus transmission

Abstract

The newly introduced castor bean whitefly (CBW) Trialeurodes ricini (Misra) 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 the castor bean whitefly. Electrophoresis of homogenates of individual T. ricini females showed that there are five different biotypes (C -C ). The predominant biotype (C 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 castor bean whitefly biotypes. PCR revealed that the five biotypes of T. ricini are viruliferous. To evaluate the efficiency of the predominant T. ricini biotype for transmitting the tomato yellow leaf 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 inoculation access period was lengthened and reached a maximum after 4 h. The obtained symptomatological results were also confirmed by PCR. 1 5 1