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

• Author(s): Castle, Steven; Naranjo, Steve; Toscano, Nick;
• Abstract: The spatial distribution of nymphal and adult glassy-winged sharpshooter (GWSS) was studied in citrus orchards in Riverside, CA using a bucket sampling method. On average, about 2.4 times as many GWSS were collected in the upper half of the tree canopy compared with the lower half and about 1.6 times as many were collected on the south side of trees compared with the north side. The coefficient of variation (CV=SD/mean) was nearly 2 times lower in samples taken from the upper half of the canopy compared with the lower half, but there were no differences in the CVs among different compass directions. These findings were used to refine the sample unit for sampling GWSS in citrus. Sticky trap catches of GWSS adults were highly correlated with on-plant GWSS populations within a given year but the relationship was variable between years. Based on the bucket sampling method we present density-dependent sample size and sample cost estimates and a preliminary sequential sampling plan for estimating relative population density of GWSS in citrus. We have applied this sampling program towards estimating the incidence of Xylella fastidiosa in GWSS adults. A progressive increase in the proportion of adults positive for X. fastidiosa occurred from the time of adult emergence in late June, 2002 through April, 2003. The mean titer of X. fastidiosa in heads and thoraxes also increased progressively through this period, suggesting that the potential for vectoring X. fastidiosa may rise as the spring generation of adults ages.
• Publication Date: Aug 2003
• Journal: 2003 Pierce's Disease Research Symposium