KEYS TO MANAGEMENT OF GLASSY-WINGED SHARPSHOOTER: INTERACTIONS BETWEEN HOST PLANTS, MALNUTRITION AND NATURAL ENEMIES

• Author(s): Andersen, Peter; III, Russell;
• Abstract: Leafhopper vectors of Xylella fastidiosa (including GWSS) behave very differently from most herbivorous insects. GWSS and other xylophagous leafhoppers have evolved many unusual adaptations such as host switching to maximize nutrient uptake, unprecedented assimilation efficiency of nutrients, and excretion of ammonia that enable GWSS to subsist on xylem fluid. The physiology and behavior of GWSS that make it an efficient vector also make it less amenable to conventional management tactics. Adult GWSS may feed on hundreds of different host species, are long lived and exceptionally mobile and fecund. Natural seasonal fluctuations in plant xylem chemistry determine the seasonal use of host plants by GWSS adults. Xylem chemistry can be affected and/or manipulated by environmental factors, culture and management practices (fertilizer, water, pruning, rootstock) and weather extremes. Xylem fluid has the most dilute concentrations of dietary nitrogen and carbon of any plant tissue. Malnutrition is a primary source of mortality of immature GWSS. The nutrient requirements of immature GWSS are different and much more restricted than those of adults such that successful development might often require host switching. Whereas adult GWSS utilize many different host species, early instar nymphs survive and develop on only a few. GWSS females select both feeding hosts and ovipositional hosts, yet the interactions between these two choices may be complex and conflicting. We have established that adults prefer to feed on xylem fluid with specific chemical characteristics (high amide concentrations). However, nymphs develop poorly on these high amide diets. Nymphs develop more successfully on xylem fluid with low amide concentrations and proportionally higher concentrations of many of the more dilute amino acids that are deemed essential for the development of most insects. We have also established the physiological basis for this phenomenon: adults can efficiently use nitrogen and carbon from high amide concentrations, whereas young developing nymphs cannot. Females can consume more nutrients (thus, produce more eggs) on high amide diets, yet oviposition on these same hosts will result in up to 100% nymphal mortality (from malnutrition). Oviposition (as it affects parasitism rate) and survivorship of nymphs (malnutrition) are key mortality factors for GWSS with potential for manipulation to suppress leafhopper populations and X. fastidiosa diseases. It is these important key interactions and identification of the host plant species important in mediating such interactions that must be elucidated to manage GWSS in any geographical location.
• Publication Date: Dec 2001
• Journal: 2001 Pierce's Disease Research Symposium