Biological control of water hyacinth, Pontederia crassipes (C. Mart.) Solms (Pontederiaceae), in California: release and re-distribution of biological control agents 1987–2006

Abstract. Water hyacinth, Pontederia crassipes (C. Mart.) Solms (Pontederiaceae), is a serious aquatic weed in lakes, ponds, and waterways in California and around the world. Three insects, the weevils Neochetina eichhorniae Warner, 1970, Neochetina bruchi Hustache, 1926 (Coleoptera: Brachyceridae), and a leaf moth Niphograpta albiguttalis (Warren, 1889) (Lepidoptera: Crambidae) were released at four sites in 1982–1987 for the biological control of water hyacinth in the Sacramento-San Joaquin River Delta. Here we report on statewide efforts to distribute the biological control agents outside the Delta and subsequent surveys to determine insect establishment. From 1987–2006, the three insects were redistributed to seven locations in five counties (Fresno, Los Angeles, Merced, Sacramento, and Santa Cruz) in California. Surveys in 2018–2020 found both Neochetina weevils at two locations in Merced County and one location in Sacramento County. No weevils were found at release locations in the upper San Joaquin River and associated waterways in western Fresno County or at the release location in Santa Cruz County. Plants at the release locations in Los Angeles County and eastern Fresno County had been eradicated and not sampled in this survey. These recoveries expand the known locations of Neochetina weevils in central California. The hyacinth moth, N. albiguttalis, was not recovered.