BIOLOGICAL AND MOLECULAR STUDIES ON THE TOXIC EF-FECT OF VEGETATIVE INSECTICIDAL PROTEIN (VIPs) OF Ba-cillus thuringiensis EGYPTIAN ISOLATES AGAINST WHITEFLIES

Whitefly Bemisia tabaci (Gennadius) transmitted geminiviruses cause epidemics in vegetable and fiber crops. It can infect more than 600 species of host plants. It also considered as the major vector transmitting various types of geminiviruses such as tomato yellow leaf curl virus (TYLCV) which cause great damage to tomatoes crop. Previous studies have reported that the vegetative insecticidal proteins (VIPs) of Bacillus thuringiensis (Bt) revealed insecticidal activity against different insect species. In this study, two local isolates of B. thuringiensis named BtC-18 and BtDI-29 were screened for the insecticidal activity of VIPs against whitefly population. Analysis of median lethal concentration (LC50) revealed that B. thuringiensis strain BtC-18 is more potent and toxic than BtDI-29 strain against whiteflies with an estimated LC50 of 90 ppm and 160 ppm for BtC-18 and BtDI-29, respectively. However, the median lethal time (LT50) value did not show significant difference between both isolates. PCR analysis of vip genes confirmed the presence of vip1, vip2 and vip3 genes on BtC-18 genome. Proteins extract from the BtC-18 culture pellet were further purified by 80% saturation of ammonium sulfate precipitation. The purified protein showed a clear band at 88 KDa corresponding to Vip3A protein as previously demonstrated. The LC50 of the purified band at 88KDa showed insecticidal activity against white fly with an estimated LC50 of 898 ppm.