Evidence of Establishment of Bagous hydrillae (Coleoptera: Curculionidae), a Biological Control Agent of Hydrilla verticillata (Hydrocharitales: Hydrocharitaceae) in North America?

ABSTRACT The semi-aquatic weevil Bagous hydrillae was released during 1991–1996 at 19 sites in 4 states in attempts to control the aquatic weed hydrilla, Hydrilla verticillata. Fourteen of the sites were in Florida, 2 each in Texas and Georgia and one site in Alabama. Over 320,000 adult weevils were included in these releases. Despite the fact that a few adults were recovered as late as 4.5 yr post-release, presence of permanent, self-perpetuating populations was never confirmed. Then, during 2009 adult B. hydrillae were collected in southern Louisiana, at least 580 km from the nearest release site and 13 yr after attempts to establish this insect had terminated. This suggests that earlier recoveries were indicative of successful establishment and that this weevil species has persisted and dispersed widely in the southeastern USA. Nonetheless, there is no evidence that B. hydrillae has had a suppressive effect on hydrilla.