Recent epidemics of Pierce’s disease of grapevine in California vectored by Homalodisca coagulata (Say), an invasive vector species, have characteristics that differ from epidemics involving native vectors. Among these differences are the longer distances and greater speed that the disease is spread by H. coagulata. In this investigation, we used yellow sticky traps to study the seasonal dispersion activity of H. coagulata in a southern California grape-growing area in which an epidemic of Pierce’s disease has caused large losses. For 21 mo, we monitored adult H. coagulata at the edges of vineyards bordering citrus, an important crop host, natural coastal sage scrub vegetation, and natural riparian vegetation. We also monitored H. coagulata dispersion from 0 to 40 m into vineyards. Finally, we examined the vertical dispersion of H. coagulata adults into grapevines through a season. This investigation showed that H. coagulata is associated with citrus, from where it disperses deep into vineyards, and not just the vineyard edge as with Pierce’s disease vectors that are native to California. Peak dispersion into vineyards occurred in the summer. Another period of H. coagulata activity occurred in the winter in vineyards bordering citrus. Through the period of peak flight activity, 97% of all H. coagulata adults trapped between 1 and 7 m were caught at an altitude of 5 m or lower, suggesting the potential of a barrier as a management tactic to keep H. coagulata out of vineyards.
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Vol. 96 • No. 5