A majority of plant viruses are dependent on vectors for their transmission and survival. Insects, mites, nematodes and protists all mediate the transmission of plant viruses. Insects are the most common of the vectors and, among these, aphids account for the transmission of 50% of the insect-vectored viruses (Brunt et al., 1996; Nault, 1997).
Aphids are exquisitely designed for their roles as vector. Piercing–sucking mouthparts facilitate the delivery of virions into plant cells without causing irrevocable damage. With the option of asexual reproduction, aphid populations can increase at extraordinarily high rates, thereby potentiating disease epidemics and furthering the short- and long-distance spread of viruses.
Additionally, aphids are globally distributed and there are more than 200 vector species identified, a number that is most likely a gross underestimate (Brunt et al., 1996; Eastop, 1983; Hull, 2002; Nault, 1997).