DISPERSAL AND MOVEMENT OF THE GLASSY-WINGED SHARPSHOOTER AND ASSOCIATED NATURAL ENEMIES IN A CONTINUOUS, DEFICIT-IRRIGATED AGRICULTURAL LANDSCAPE

• Author(s): Groves, Russell; Hagler, James; Johnson, Marshall; Kruegner, Rodrigo; Luck, Robert; Morgan, David; Morse, Joseph; Nadel, Hannah; Stenger, Drake;
• Abstract: A combination of field and laboratory experiments in this study have been designed to advance our understanding of the operative host-plant factors utilized by adult glassy-winged sharpshooters (GWSS) and associated natural enemies as long-range cues to locate feeding and oviposition hosts in a complex agricultural landscape. Specifically, a second year of field studies have been conducted to determine the influence of continuous deficit irrigation regimes implemented in sweet orange cv. Valencia oranges on the population dynamics of GWSS and other associated natural enemies. Dispersal and population dynamics of GWSS were monitored under continuous irrigation treatments receiving 60%, 80%, and 100% of evapo-(transpiration (ET)c() rates. Similar to the results obtained in our 2005 season, citrus trees irrigated at 60% ET)c had warmer leaves, significantly higher xylem matric potential, and fewer adult and immature GWSS than experimental trees irrigated (with 80% and 100% ET)c(. Mean numbers of adult and nymphal GWSS collected from beat samples and observed in visual inspections were numerically higher in the 80% versus 100% ET)c treatments. In caged experiments using sweet orange cv. Washington navel and avocado cv. Hass maintained under different continuous deficit irrigation illustrated GWSS population shifts that occurred between plants. Adult GWSS showed a preference for contact with surplus-irrigated plants of both species compared with plants under continuous deficit irrigation, with a stronger response evident in the avocado trials. During preliminary nutrition trials with overwintered adults, GWSS that landed on plants showed a slight preference for settling on plants fertilized with ammonium versus nitrate averaging over 3 trials. An olfactometer system for studying the response of GWSS to host-plant volatiles has been built and the airflow dynamics adjusted to equally integrate odor fields from humidity or volatile sources. However, evaluation of the data (number of insects landing on the target) to date shows no conclusive differences among a variety of treatments, suggesting that GWSS may not use olfactory cues during host location, or that olfaction is used only in conjunction with visual cues. Identifying how the dispersing lifestages of GWSS locate and exploit specific host species will begin to provide the necessary information required to develop strategies for control of this highly mobile insect and the spread of Xylella fastidiosa into susceptible crops.
• Publication Date: Nov 2006
• Journal: 2006 Pierce's Disease Research Symposium