Invisible invaders: Insect-transmitted viruses threaten agriculture

Abstract

The vast movement of people and agricultural products between distant geographical regions has created unprecedented opportunities for introducing plant viruses and the insects that carry them (vectors) to new areas. Outbreaks of new viruses may be favored in these agroecosystems by crop susceptibility, the presence of particular weeds and certain agricultural practices. In some cases, conditions in these ecosystems may be ideal for the emergence of altered plant viruses and new virus/vector relationships. This may result in the appearance of insect-transmitted plant viruses in crops and regions where they have not been seen before. Because plant viruses and their insect vectors are intimately linked, the status of both must be considered in formulating strategies to prevent or slow their introduction, as well as to manage any invasions. To illustrate these points we highlight two situations that could threaten California agriculture. First, a devastating plant virus, tomato yellow leaf curl geminivirus, is not present in California, but an insect (the silverleaf whitefly) that transmits it is present. Second, the brown citrus aphid is not present in California, but a citrus virus (citrus tristeza closterovirus) that this insect efficiently spreads, is present.