title: Direct Evidence of Egestion and Salivation of Xylella fastidiosa Suggests Sharpshooters Can Be "Flying Syringes".
abstract: Xylella fastidiosa is unique among insect-transmitted plant pathogens because it is propagative but noncirculative, adhering to and multiplying on the cuticular lining of the anterior foregut. Any inoculation mechanism for X. fastidiosa must explain how bacterial cells exit the vector's stylets via the food canal and directly enter the plant. A combined egestion-salivation mechanism has been proposed to explain these unique features. Egestion is the putative outward flow of fluid from the foregut via hypothesized bidirectional pumping of the cibarium. The present study traced green fluorescent protein-expressing X. fastidiosa or fluorescent nanoparticles acquired from artificial diets by glassy-winged sharpshooters, Homalodisca vitripennis, as they were egested into simultaneously secreted saliva. X. fastidiosa or nanoparticles were shown to mix with gelling saliva to form fluorescent deposits and salivary sheaths on artificial diets, providing the first direct, conclusive evidence of egestion by any hemipteran insect. Therefore, the present results strongly support an egestion-salivation mechanism of X. fastidiosa inoculation. Results also support that a column of fluid is transiently held in the foregut without being swallowed. Evidence also supports (but does not definitively prove) that bacteria were suspended in the column of fluid during the vector's transit from diet to diet, and were egested with the held fluid. Thus, we hypothesize that sharpshooters could be true "flying syringes," especially when inoculation occurs very soon after uptake of bacteria, suggesting the new paradigm of a nonpersistent X. fastidiosa transmission mechanism.
authors.affiliation: First and third authors: U.S. Department of Agriculture (USDA)-Agricultural Research Service (ARS), San Joaquin Valley Agricultural Sciences Center, 9611 S. Riverbend Ave., Parlier, CA 93648-9757; second author: University of Florida, Department of Entomology, Citrus Research and Education Center, 700 Experiment Station Rd., Lake Alfred, FL 33850; and fourth and fifth authors: USDA-ARS, U.S. Horticultural Research Lab., Subtropical Insects and Horticulture Research, 2001 S. Rock Rd., Ft. Pierce, FL 34945.
authors.forename: Elaine A
authors.initials: EA
authors.lastname: Backus
authors.affiliation: First and third authors: U.S. Department of Agriculture (USDA)-Agricultural Research Service (ARS), San Joaquin Valley Agricultural Sciences Center, 9611 S. Riverbend Ave., Parlier, CA 93648-9757; second author: University of Florida, Department of Entomology, Citrus Research and Education Center, 700 Experiment Station Rd., Lake Alfred, FL 33850; and fourth and fifth authors: USDA-ARS, U.S. Horticultural Research Lab., Subtropical Insects and Horticulture Research, 2001 S. Rock Rd., Ft. Pierce, FL 34945.
authors.forename: Holly J
authors.initials: HJ
authors.lastname: Shugart
authors.affiliation: First and third authors: U.S. Department of Agriculture (USDA)-Agricultural Research Service (ARS), San Joaquin Valley Agricultural Sciences Center, 9611 S. Riverbend Ave., Parlier, CA 93648-9757; second author: University of Florida, Department of Entomology, Citrus Research and Education Center, 700 Experiment Station Rd., Lake Alfred, FL 33850; and fourth and fifth authors: USDA-ARS, U.S. Horticultural Research Lab., Subtropical Insects and Horticulture Research, 2001 S. Rock Rd., Ft. Pierce, FL 34945.
authors.forename: Elizabeth E
authors.initials: EE
authors.lastname: Rogers
authors.affiliation: First and third authors: U.S. Department of Agriculture (USDA)-Agricultural Research Service (ARS), San Joaquin Valley Agricultural Sciences Center, 9611 S. Riverbend Ave., Parlier, CA 93648-9757; second author: University of Florida, Department of Entomology, Citrus Research and Education Center, 700 Experiment Station Rd., Lake Alfred, FL 33850; and fourth and fifth authors: USDA-ARS, U.S. Horticultural Research Lab., Subtropical Insects and Horticulture Research, 2001 S. Rock Rd., Ft. Pierce, FL 34945.
authors.forename: J Kent
authors.initials: JK
authors.lastname: Morgan
authors.affiliation: First and third authors: U.S. Department of Agriculture (USDA)-Agricultural Research Service (ARS), San Joaquin Valley Agricultural Sciences Center, 9611 S. Riverbend Ave., Parlier, CA 93648-9757; second author: University of Florida, Department of Entomology, Citrus Research and Education Center, 700 Experiment Station Rd., Lake Alfred, FL 33850; and fourth and fifth authors: USDA-ARS, U.S. Horticultural Research Lab., Subtropical Insects and Horticulture Research, 2001 S. Rock Rd., Ft. Pierce, FL 34945.
authors.forename: Robert
authors.initials: R
authors.lastname: Shatters
mesh_terms: D000818:Animals; D006430:Hemiptera / Q000166:cytology / Q000382:microbiology*; D007303:Insect Vectors / Q000166:cytology / Q000382:microbiology*; D010935:Plant Diseases / Q000382:microbiology* / Q000706:statistics & numerical data; D012472:Salivation; D044167:Xylella / Q000502:physiology*
keywords: Pierce’s disease; acquisition