The long-range dispersal of plant viruses by arthropod vectors

Many plant viruses have winged or otherwise windborne insect or mite vectors that can fly or be blown far, suggesting that at least some of these viruses can be transported over great distances. However, this is difficult to substantiate and the evidence is largely circumstantial and mainly derived from studies on beet curly top and a few other viruses transmitted by leafhoppers, planthoppers or aphids. This review considers the evidence for long-range dispersal of plant viruses in an overall ecological context that is also applicable to other types of host and pathogen. All the known or suspected examples are attributed to particularly active migrant forms of species that are well adapted for colonizing new habitats as the original ones deteriorate. It is concluded that distant spread occurs more frequently than is generally supposed and that it is an extreme expression of dispersive processes that occur repeatedly but over generally shorter distances. These conclusions are shown to be compatible with the view that plant viruses mainly cause ‘ crowd diseases ’ that do not spread far in any considerable amount and are amenable to control by isolation and other measures of crop hygiene.