|Groves,, Russell - UNIV OF WISCONSIN|
|Johnson,, Marshall - UC RIVERSIDE|
|Flores,, Arnel - UC RIVERSIDE|
|Morse,, Joseph - UC RIVERSIDE|
Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 10, 2009
Publication Date: June 1, 2009
Citation: Krugner, R., Groves,, R.L., Johnson,, M.W., Flores,, A.P., Hagler, J.R., Morse,, J.G. 2009. Seasonal Population Dynamics of Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae) in Sweet Orange Trees Maintained under Continuous Deficit Irrigation. Journal of Economic Entomology. 102(3):960-973. Interpretive Summary: A field study was conducted to determine effects of plant water stress on host selection behavior and population dynamics of the glassy-winged sharpshooter (GWSS). Visual inspection, beat net sampling, and trapping by yellow sticky cards documented population dynamics of GWSS in a citrus orchard irrigated with 100% of crop evapotranspiration (ETc), 80 percent ETc and 60 percent ETc. GWSS population density and measurements of plant condition (e.g., leaf temperature and water potential) were recorded weekly. GWSS populations were negatively affected by severe plant water stress (60 percent ETc) and positively affected by moderate plant water stress (80 percent ETc). Citrus trees irrigated at 60 percent ETc had significantly warmer leaves and lower xylem matrix potential. Fewer GWSS egg masses, nymphs, and adults were found on trees irrigated at 60 percent ETc than at 80 percent ETc. The adult GWSS population was reduced, on average, by 50 percent in trees under severe water stress. However, the total number of fruit and number of fruit across several grade categories was also substantially reduced in the 60 percent ETc treatment. A more complete understanding of the effect of plant water stress on GWSS host selection behavior may improve GWSS control and limit spread of Xylella fastidiosa to susceptible crops.
Technical Abstract: A two-year study was conducted in a citrus orchard [Citrus sinensis (L.) Osbeck cv. ‘Valencia’] to determine influence of plant water stress on population dynamics of glassy-winged sharpshooter (GWSS), Homalodisca vitripennis (Germar). Experimental treatments included irrigation at 100% of the crop evapotranspiration rate (ETc) and continuous deficit-irrigation regimes at 80 and 60% ETc. Microclimate and plant conditions monitored included temperature and humidity in the tree canopy, leaf surface temperature, water potential, and fruit quality and yield. GWSS population density and activity were monitored weekly by a combination of visual inspection, beat net sampling, and trapping. GWSS populations 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, lower xylem water potential, and consequently hosted fewer GWSS eggs, nymphs, and adults than trees irrigated at 80% ETc. Citrus trees irrigated at 100% ETc hosted similar numbers of GWSS as trees irrigated at 60 and 80% ETc. Irrigation treatments did not affect populations of monitored natural enemies. Although the adult GWSS population was reduced, on average, by 50% 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.