Range expansion of Rhinocyllus conicus froelich on musk thistle in Northwest Louisiana

In 1975, adult musk thistle head weevils, Rhinocyllus conicus Froelich, were released in Northwest Louisiana for control of musk thistle, Carduus nutans L. Subsequent releases were made in 1976 south of Hanna, LA, and in 1994 near Elm Grove, LA. A 16-site survey in 1994 examined the abundance and distribution of R. conicus in Northwest Louisiana. On 26 April and 3 May 2001, a new survey was conducted to examine changes in the population and distribution of R. conicus since the 1994 survey. Results indicated that the musk thistle head weevil continues to expand its range and, within its range, the population of the weevil continues to increase. The percentage of infested flowerheads increased from 29.8% to 75.3% from 1994 to 2001, while numbers of R. conicus larvae per infested flowerheads increased from 1.5 to 9.6 during the same period.