Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/13/2008
Publication Date: 6/1/2008
Citation: Nadel, H., Seligmann, R., Johnson, M.W., Hagler, J.R., Stenger, D.C., Groves, R.L. 2008. Effects of citrus and avocado irrigation and nitrogen-form soil amendment on host selection by adult Homalodisca vitripennis. Environmental Entomology. 37(3):787-795. Interpretive Summary: The glassy-winged sharpshooter (GWSS) feeds on the xylem plant sap that carries water from the roots to the rest of the plant, and is capable of infecting some crop and ornamental plants with a bacterium that causes Pierce’s disease, oleander leaf scorch, and other diseases. Field studies strongly suggested that GWSS move towards recently irrigated citrus under hot, dry conditions in southern California, presenting the likelihood that they can detect and prefer to stay on adequately watered plants. We tested whether adult GWSS prefer to land and lay eggs on adequately watered or water stressed plants in cages, using potted citrus and avocado, and their capacity to feed on water stressed plants. We also tested whether GWSS showed any preference to citrus treated with two types of common fertilizers added to irrigation water. T These results increase our understanding of how and why GWSS move around diverse agricultural landscapes in southern California, and provide options to manage irrigation practices to restrict GWSS movement and abundance with the goal of reducing disease outbreaks.
Technical Abstract: Host plant water status is thought to influence dispersal and movement of Homalodisca vitripennis Germar, especially where plants are grown under high evaporative demand. The leafhopper transmits the bacterial pathogen, Xylella fastidiosa Wells et. al, to economically important susceptible plants. Preference of adult H. vitripennis for plants grown under different water deficit regimes and two soil amendments was studied under laboratory conditions. Potted citrus and avocado were used separately in cage choice tests to determine settling and oviposition host preference, and feeding activity was quantified via excreta produced by insects confined on single plants. Responses to citrus treated with two ratios of nitrate-N and ammonium-N soil amendments were also compared. The insects settled, oviposited, and fed significantly more on surplus-irrigated plants than on plants under moderate levels of continuous deficit irrigation. Citrus plants under gradual deficit irrigation (GDI) (drought) were settled and fed upon significantly less than the control when GDI plant water consumption declined to 40% of the control and the xylem water potential declined to about -10 bar. The insects settled on GDI avocado significantly less than the control, but feeding activity was not statistically different between the treatments. No statistical differences in settling, oviposition, or feeding activity were detected in citrus fertigated with 26:1 or 1:1 ratios of nitrate-N and ammonium-N. Feeding activity on both plant species was diurnal, and although females fed more than males, sex differences were not significant. The potential for management of H. vitripennis movement in southern California through deficit irrigation practices is discussed.