Technical Abstract: Technical Abstract: Criniviruses are an emerging genus worldwide, with numerous new species having been identified within the past several years, often causing symptoms that are readily mistaken for physiological or nutritional disorders or pesticide phytotoxicity. Depending on the host plant affected, these symptoms include interveinal yellowing of leaves, an associated loss of photosynthetic capability, leaf brittleness, reduced plant vigor, yield reductions, and early senescence. Crinivirus epidemiology is impacted not only by vector-movement of viruses, but also by factors such as virus competitiveness in host plants. Studies demonstrated transmission efficiency and virus persistence in the vector varies significantly among the different whitefly vectors of these viruses. In addition, virus accumulation and vector transmission efficiency varied by host plant, and virus accumulation and transmission efficiency were altered during mixed infections. It is likely that competitiveness or fitness of each crinivirus varies among different host plant species, and may be influenced by factors such as plant age or which virus became established first. Co-infection of two viruses may increase the potential for genetic recombination or pseudo-recombination between related crinivirus species, and may contribute to selection pressure leading to emergence of new strains or species with altered host range, symptomatology or vector specificity.