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The eriophyid mite Phyllocoptes fructiphilus is the vector of rose rosette disease (RRD). The mite occurs naturally on several wild roses and on multiflora rose. P. rosarum is a related eriophyid mite found on multiflora and other rose plants. A successful mass rearing program was developed and a rearing arena designed to allow observation of individual mites. Biological studies were conducted of both mites including life history, sex ratio, hibernation site, effect of temperature on egg laying and rate of development, and host range. Effect of relative humidity on P. rosarum was studied. Transmission trials were conducted both in the Greenhouse and in the field. Attempts were made to locate the RRD pathogen in the mite vector using transmission electron microscopy. Carbohydrate analysis of infected and healthy multiflora rose tissue was compared.