Geminiviruses are transmitted by whiteflies, leafhoppers, or treehoppers. The whitefly species Bemisia tabaci (Gennadius) is the most efficient vector of Subgroup III geminiviruses. An isolate of Abutilon mosaic virus (AbMV), a bipartite geminivirus, was not detectable in the DNA extract from insects by Southern blot analysis, nor was the isolate transmissible by the B-biotype of B. tabaci, although the virus DNA was amplified (by PCR) from some insects. In contrast, Sida golden mosaic virus (SiGMV-Co), a closely related geminivirus, was acquired and transmitted by B. tabaci to various host plants. The coat protein of AbMV was replaced with that of SiGMV-Co. The resulting chimeric AbMV was acquired and transmitted to various host plants by B. tabaci, indicating that the coat protein plays an essential role in the transmission process by B. tabaci.