OVERWINTERING AND ESTABLISHMENT POTENTIAL OF BAGOUS-AFFINIS (COLEOPTERA, CURCULIONIDAE) ON HYDRILLA-VERTICILLATA (HYDROCHARITACEAE) IN NORTHERN CALIFORNIA

Bagous affinis Hustache (Coleoptera: Curculionidae) has potential as a biological control agent for subterranean turions (also called tubers) of hydrilla (Hydrilla verticillata (L.f.) Royle; Hydrocharitaceae). The ability of B. affinis to overwinter and establish was investigated at 2 sites in northern California; a pond in Calaveras County and the Chowchilla River in Madera County. In cage studies conducted at the pond, B. affinis survived the winter for 2 seasons. After releases at the pond, B. affinis successfully reproduced and survived during the summer of 1992. Weevil larvae had damaged both sentinel and native tubers at the site. In the spring, following the release of B. affinis at the pond, a light trap and baited shelter traps were used to detect weevils that had overwintered naturally at the site. No weevils were recovered. At the Chowchilla River site, B. affinis failed to establish, possibly due to a lack of tubers in the section of the river where the releases were made.