The virus itself is an extremely small, nearly spherical particle (its diameter is only 0.000001 inch) which can be spread by several aphid species that colonize potato, with the green peach aphid being the most efficient. The insect vector is absolutely essential to spread because mechanical transmission, like that which occurs when the leaves of an infected plant rub on a healthy one, simply does not occur with PLRV. The infection process is actually quite complicated with this virus. First the aphid must acquire the virus by feeding on a PLRV infected plant. Then the virus must circulate from the gut of the aphid, through the circulatory system until it finally gets into the salivary glands, from which it can be excreted when the aphid feeds on healthy plants. Only after this has happened can the aphid spread the virus. This sequence of events may require 24 hr. or more to occur. Unfortunately, once an aphid becomes infected, it remains so for the rest of its life. Spread of the virus between plants within a field and between fields can be done by the winged forms of the aphid but most spread within a field, especially from infected plants to nearby, healthy ones, is accomplished by the wingless forms.