Prokelisia marginata is a planthopper native to the Atlantic Coast of North America, from Massachusetts to Florida and Mississippi where it feeds on Spartina alterniflora. It is a small insect, 2-4 mm. It had been considered native San Francisco Bay, where it feeds on native S. foliosa as well as introduced S. alterniflora. However, it was probably been introduced with the latter plant, which was brought from the Atlantic coast for wetland restoration (1973, Daehler and Strong 1994). We have not found records of P. marginata from locations on the coast south of San Francisco Bay, where S. foliosa grows. This absence lends support to the introduced status of Prokelisia in San Francisco Bay. More recently, P. marginata has appeared in Europe, in the Algarve, Portugal and nearby areas of Spain (~1999), Slovenia, on the Adriatic Sea., and in Southampton and Pole, southern England, in 2008 (Bolton 2008; National Museum Wales 2008). Its native food is S. alterniflora, but it also feeds on S. maritima and S. anglica in Europe, and S. foliosa in California. In 2000, and 2001.,15,000 and 150,000 P. marginata were released at 3 sites around Willapa Bay for biocontrol of Spartina. However, effects of biocontrol by Prokelisia were limited, and herbicide use was resumed in 2007.