ECOLOGY AND BEHAVIOR Seasonal Population Dynamics of Homalodisca vitripennis (Hemiptera: Cicadellidae) in Sweet Orange Trees Maintained Under Continuous Deficit Irrigation

A 2-yr study was conducted in a citrus orchard (Citrus sinensis L. Osbeck cultivar Valencia) todetermine the inßuenceofplantwater stresson thepopulationdynamicsofglassy-winged sharpshooter,Homalodisca vitripennis (Germar). Experimental treatments included irrigation at 100% of the crop evapotranspiration rate (ETc) and continuous deÞcit-irrigation regimens 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. Glassy-winged sharpshooter population densities and activity were monitored weekly by a combination of visual inspections, beat net sampling, and trapping. Glassy-winged sharpshooter populations were negatively affected by severe plant water stress; however, population densities were not linearly related to decreasing water availability in plants. Citrus trees irrigated at 60% ETc had signiÞcantly warmer leaves, lower xylemwater potential, and consequently hosted fewer glassy-winged sharpshooter eggs, nymphs, and adults than trees irrigated at 80% ETc. Citrus trees irrigated at 100% ETc hosted similar numbers of glassy-winged sharpshooter stages as trees irrigated at 60% ETc and a lower number of glassy-winged sharpshooter nymphs than the 80% ETc treatment, speciÞcally during the nymphal density peak in mid-April to early July. Irrigation treatments did not affect populations of monitored natural enemies. Although the adult glassy-winged sharpshooter 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 signiÞcantly lower in the 60% ETc than in the 80 and 100% ETc irrigation treatments.