Insect Vectors of Phytoplasmas

The principal means of dissemination of phytoplasmas is by insect vectors. The interactions between phytoplasmas and their insect vectors are, in some cases, very specific, as is suggested by the complex sequence of events that has to take place and the complex form of recognition that this entails between the two species. The commonest vectors, or at least those best known, are members of the order Homoptera of the families Cicadellidae, Cixiidae, Psyllidae, Cercopidae, Delphacidae, Derbidae, Menoplidae and Flatidae. The family with the most known species is, without doubt, the Cicadellidae (15,000 species described, perhaps 25,000 altogether), in which 88 species are known to be able to transmit phytoplasmas. In the majority of cases, the transmission is of a trans-stage form, and only in a few species has transovarial transmission been demonstrated. Thus, two forms of transmission by insects generally are known for phytoplasmas: trans-stage transmission occurs for most phytoplasmas in their interactions with their insect vectors, and transovarial transmission is known for only a few phytoplasmas.