Transmission of Xylella fastidiosa to oleander by the glassywinged sharpshooter, Homalodisca coagulata

Studies were conducted to investigate the transmission of the oleander leaf scorch (OLS) pathogen to oleander (Nerium oleander L.) plants by sharpshooters. OLS is incited by a strain of the bacterial plant pathogen Xylella fastidiosa Well. The glassywinged sharpshooter, Homalodisca coagulata (Say), is a principal vector of this pathogen in California. In these studies, three cultivars of oleander were exposed to sharpshooters that had previously fed upon OLS-infected oleander plants. Sharpshooters were subsequently caged on healthy oleander plants individually or in groups of three. Plants were observed for symptoms of disease, and ELISA was used to test for the presence of X. fastidiosa. The probability of infection did not differ significantly when plants were inoculated with one insect (83 %) or with three (94 %). However, higher plant mortality rates were observed on plants inoculated with three insects, indicating that a greater number of infection sites may hasten plant death. Although all oleander cultivars were equally susceptible to inoculation by sharpshooters, 'Ruby Lace' plants were less symptomatic and had a higher level of survival after one year than 'Hardy Pink' and 'Hardy Red'. When given a choice of the three cultivars to feed on, the number of insects feeding did not differ among cultivars at 24 or 48 hours after exposure.