Potato virus diseases are spread by

Potato virus diseases are spread by Aphids.
Aphids are sap-sucking insects and have piercing, sucking mouthparts. Their mouthparts include a needle-like stylet that allows the aphid to access and feed on the contents of plant cells.
Potato virus is spread naturally in a non-persistent manner by many aphid species and can be mechanically transmitted. The virus is transmitted when an aphid initially probes the plants.
The most important viruses transmitted by aphids to potatoes in Scotland are potato leaf roll virus (PLRV), potato virus Y (PVYO and PVYN (veinal necrosis)) and potato virus A (PVA).