ESTABLISHMENT OF RHINOCYLLUS-CONICUS FROELICH CURCULIONIDAE, COLEOPTERA ON CARDUUS-MACROCEPHALUS IN TEXAS

The number of counties in Texas with infestations of an exotic thistle , Carduus macrocephalus (Desf.) (Asteraceae), increased from one to tw enty-eight between 1975 and 1993. The weevil Rhinocyllus conicus Froel ich was released as a biological control agent on C. macrocephalus in Ellis County, Texas, in 1984 and Kerr County, Texas, in 1987. A popula tion of the weevil established at the Kerrville site by 1992 and studi es to evaluate its effectiveness were conducted in 1992 and 1993. In 1 992, female weevils laid 606 eggs per plant, and larvae infested 89% o f the flowerheads. In 1993, females laid 346 eggs per plant, and infes ted 92% of the heads. Seed production of infested plants was reduced 8 1% in 1992 and 90% in 1993 compared with that of uninfested plants. Th e number of eggs and larvae was greatest in the terminal heads and seq uentially decreased in lateral, sublateral, and axillary heads. Weevil s migrated 2.5 km from the study site in 1992 and 5.3 km from the site in 1993. In 1992, additional releases of R. conicus were made in Kerr , Gillespie, and Menard counties. This represents the first release an d establishment of a biological control agent on Carduus in Texas.