SAMPLING, SEASONAL ABUNDANCE, AND COMPARATIVE DISPERSAL OF GLASSY-WINGED SHARPSHOOTERS IN CITRUS AND GRAPES: DISPERSAL PROGRESS REPORT

Authors: Blackmer, Jacquelyn; Hagler, James

Submitted to: CDFA Pierce's Disease Control Program Research Symposium
Publication Type: Proceedings
Publication Acceptance Date: 12/1/2003
Publication Date: 3/1/2004
Citation: Blackmer, J.L., Hagler, M. 2004. Sampling, seasonal abundance, and comparative dispersal of glassy-winged sharpshooters in citrus and grapes: dispersal progress report. CDFA Pierce's Disease Control Program Research Symposium. p. 204-206.

Interpretive Summary: Environmental variables and host-plant quality influence insect population dynamics and the timing and extent of their dispersal. An understanding of how these factors influence glassy-winged sharpshooter (GWSS) development and movement is needed to better predict the spread of Pierce's Disease and to aid area-wide management strategies. We investigated how plant factors and environmental parameters influenced sharpshooter population dynamics and movement in a citrus grove setting. Number of egg masses and adults were counted on branches that were sampled for xylem sap. Collection date, tree, and cardinal direction were noted, and xylem pressure, and amino acids were measured. In conjunction with xylem sap collections, movement of sharpshooters was monitored with yellow and clear sticky traps at 4-h intervals during the day and throughout the night. During replicated sampling periods, 40 times more sharpshooters were trapped on yellow sticky traps in comparison to clear sticky traps and the majority, regardless of sex, were trapped between 1000 and 1400 h. Higher trap catches were associated with increasing temperatures above 18ºC, but were not significantly associated with changes in wind speed, relative humidity or barometric pressure. Trap catches varied significantly over the trapping season, but did not differ due to trap location, indicating that there was no strong edge effect for GWSS. Xylem pressure and amides varied due to collection date and time of day, and xylem pressure was positively correlated with trap catches. Osmolality, total amino acids, essential amino acids, and percent amides had no apparent relationship with trap catch. GWSS egg counts varied due to collection date and cardinal direction, with the majority of eggs observed on the east and south sides of the trees.

Technical Abstract: Environmental variables and host-plant quality influence insect population dynamics and the timing and extent of their dispersal. An understanding of how these factors influence Homalodisca coagulata, glassy-winged sharpshooter (GWSS) development and movement is needed to better predict the spread of Pierce's Disease and to aid area-wide management strategies. We investigated how plant factors (i.e., amino acids, osmolality, xylem pressure) and environmental parameters (i.e., wind speed, temperature, relative humidity, barometric pressure) influenced sharpshooter population dynamics and movement in a citrus grove setting. Number of egg masses and adults were counted on branches that were sampled for xylem sap. Collection date, tree, and cardinal direction were noted, and xylem pressure, and amino acids (total, essential and amides) were measured. In conjunction with xylem sap collections, movement of sharpshooters was monitored with yellow and clear sticky traps at 4-h intervals during the day and throughout the night. During replicated sampling periods, 40 times more sharpshooters were trapped on yellow sticky traps in comparison to clear sticky traps and the majority, regardless of sex, were trapped between 1000 and 1400 h. Higher trap catches were associated with increasing temperatures above 18ºC, but were not significantly associated with changes in wind speed, relative humidity or barometric pressure. Trap catches varied significantly over the trapping season, but did not differ due to trap location, indicating that there was no strong edge effect for GWSS. Relative to xylem sap collections, xylem pressure and amides varied due to collection date and time of day, and xylem pressure was positively correlated with trap catches. Osmolality, total amino acids, essential amino acids, and percent amides had no apparent relationship with trap catch. GWSS egg counts varied significantly due to collection date and cardinal direction, with the majority of eggs observed on the east and south sides of the trees.