Range Expansion ofRhinocyllus conicusFroelich1on Musk Thistle into Southwestern Arkansas2

Abstract

In 1975, adult musk thistle head weevils, Rhinocyllus conicus Froelich, were released south of Hanna, Red River Parish, LA, for control of the musk thistle, Carduus nutans L. Subsequent releases were in 1976 south of Hanna and in 1994 near Elm Grove, Bossier Parish, LA. Surveys in 2004, 2008, and 2010 examined abundance and range expansion of R. conicus in northwestern Louisiana and southwestern Arkansas. Results from these surveys were compared with surveys in 1994 and 2001. South of the Shreveport/Bossier City metropolitan area where R. conicus had initially been released, abundance increased from 1994 to 2008. From 2008 to 2010, percentage of infested flower heads decreased from 90.9 to 74%, with mean weevils per infested flower head decreasing from 12.9 to 3.9. North of the metropolitan area, where weevil infestations were lower in 1994, mean weevilinfested flower heads has increased steadily from 1994 to 2010. R. conicus continues to expand its range north into southwestern Arkansas. Three Arkansas counties, Hempstead, Lafayette, and Miller, now have established populations of R. conicus.