A vector is an organism that spreads diseases by transmitting pathogens from one host to another. Almost all plant viruses and phytopathogenic mollicutes (cell-wall-less bacteria) are transmitted by sap-sucking insects. Most of them are aphids, whiteflies, mealybugs, soft scales, leafhoppers, and planthoppers. Much research on vector transmission seeks to understand the transmission process so as to explain why only certain kinds of insects can serve as vectors and to identify factors required for transmission. Because vector eradication by applying insecticides frequently fail to control the vector-borne diseases, detailed knowledge of the relationship between vectors and pathogens shows great promise for insect-borne disease management. The course will introduce students to current advancements of related researches at the molecular, genetic, and ecological levels.