Three biological entities lie at the foundation of the Tospovirus pathosystem: thrips vectors, Tospovirus variants (species or serogroups and serotypes), and the plant species serving as hosts for both the viruses and their vectors. Epidemics can occur only when these biological components coincide in an appropriate environment. Emphasis is on diagnosis, molecular biology, nomenclature and phylogenetics, and thrips Tospovirus interactions that govern the epidemiology of these important plant viruses. -from Authors