Submitted to: CDFA Pierce's Disease Control Program Research Symposium
Publication Type: Proceedings
Publication Acceptance Date: 12/1/2007
Publication Date: 12/12/2007
Citation: Krugner, R., Nadel, H., Johnson,, M.W., Hagler, J.R., Morgan,, D., Stenger, D.C., Groves, R. 2007. Dispersal and Movement of the Glassy-winged Sharpshooter and Associated Natural Enemies in a Continuous, Deficit-irrigated Agricultural Landscape. In: Proceedings of CDFA Pierce's Disease Control Program Research Symposium, December 12-14, 2007, San Diego, California. p. 38-41
Interpretive Summary: Host-plant water status is thought to influence dispersal of the glassy-winged sharpshooter (GWSS). Laboratory and field studies were conducted to determine the effects of plant water stress on the host selection behavior and population dynamics of the GWSS. Choice tests were conducted in laboratory to evaluate GWSS settling and oviposition preference using potted ‘Washington navel’ orange maintained under different water deficit regimes. Insects settled, ovipositioned, and fed significantly more on surplus-irrigated plants than on plants under moderate deficit irrigation regimes. After 7 days under gradual deficit irrigation, water-stressed plants became significantly less preferred by GWSS than well watered plants. In the field GWSS populations were negatively affected by severe plant water stress (60% ETc) and positively affected by moderate plant water stress (80% ETc). Citrus trees irrigated at 60% ETc had significantly warmer leaves and higher xylem matrix potential. Fewer GWSS egg masses, nymphs, and adults were found on trees irrigated at 60% ETc than at 80% ETc. The adult GWSS population was reduced, on average, by 35% in trees under severe water stress. However, the total number of fruits and number of fruit across several fruit grade categories was also substantially reduced in the 60% ETc treatment. A more complete understanding of the host-plant cues that influence GWSS population dynamics may result in the development of strategies to focus control efforts, enhance the efficacy of biological control, and effectively limit the spread of Xylella fastidiosa induced diseases to susceptible crops.
Technical Abstract: Host-plant water status is thought to influence dispersal of the glassy-winged sharpshooter (GWSS). Preference of adult GWSS for citrus plants maintained under different water deficit regimes was studied under laboratory and field conditions. In laboratory studies, settling and oviposition preference were studied on potted ‘Washington navel’ orange in cage choice tests, and feeding activity was estimated via insect excreta production. A field study was conducted in a citrus orchard (‘Valencia’) to determine the influence of plant water stress on population dynamics of GWSS. Experimental treatments in this study included irrigation at 100% of the crop evapotranspiration (ETc) and continuous deficit-irrigation (CDI) regimes at 80% and 60% ETc. Plant conditions were monitored by measurements of leaf surface temperature, water potential, and fruit quality and yield. GWSS population density and activity were monitored weekly by visual inspections, beat net sampling, and trapping. In laboratory tests, insects settled, oviposited, and fed significantly more on surplus-irrigated plants than on plants under moderate CDI. Plants under gradual deficit irrigation became less preferred after 7 d. Citrus water consumption at this point declined to 40% of the control and xylem-fluid tension was estimated at 9.3 Bar. GWSS population in the field study were negatively affected by severe plant water stress; however, population density was not linearly related to decreasing water availability in plants. Citrus trees irrigated at 60% ETc had significantly warmer leaves, higher xylem matrix potential, and consequently hosted smaller numbers of GWSS eggs, nymphs, and adults than trees irrigated at 80% ETc. Citrus trees irrigated at 100% ETc hosted the same number of insects as trees irrigated at 60% and 80% ETc. Although the adult GWSS population was reduced, on average, by 35% in trees under severe water stress, the total number of fruit and number of fruit across several fruit grade categories were significantly lower in the 60% ETc than in the 80% and 100% ETc irrigation treatments.