Pests Beneficial Organisms Insect-Transmitted Diseases Management Options Other Resources Contact a Specialist Other Insect-Transmitted Diseases Throughout the world there is a long list of viruses, phytoplasmas, and other microbes that cause potato disease and that are transmitted by insects. Examples in North America include zebra chip (caused by a bacterium and transmitted by the potato psyllid), Tomato spotted wilt virus (transmitted by insects called thrips), various mild mosaic viruses such as Potato virus S and Potato virus A, and Alfalfa mosaic virus, all of which are of minor importance in the PNW.   Symptoms caused by Alfalfa mosaic virus - known as "calico" in potatoes.