Mycoplasma and allied diseases of forest trees in India have been described,mlo disease has been intensively studied in ‘sandal’ (Santalum album L.). Other forest trees showing typicalmlo etiology are ‘toon’(Toona ciliata), Acacia catechu, A. mearnsii, Eucalyptus grandis andE. tereticornis. Disease symptoms, collateral hosts, transmission tests with possible insect vectors and vector biology have been described for sandal spike disease. Reasons for contradictory results for sandal spike vectors have been discussed and possible lines of vector search for woody plants are described. Vector-host-pathogen interactions have been reviewed. During the feeding process, phloem cells are punctured, torn and disturbed by vectors. The hypertrophy of the plant cells around the site of puncture is caused by the action of injected salivary secretion. Vector borne procaryotic disease pathogens multiply within the vectors and circulate through a sequence of tissues and organs of vectors when the latent period of pathogen is long. These initiate both harmful and beneficial interactions within the vector. Possible lines of research to fill up the existing lucunae for insect vectors of mycoplasma and allied diseases of forest trees and vector-host-pathogen interactions have been discussed.