Biological control of invasive plants in California’s Delta: Past, present, and future

Authors: Pratt, Paul; Moran, Patrick; PITCAIRN, MIKE - California Department Of Food And Agriculture; Reddy, Angelica; O'BRIEN, JON - California Department Of Parks And Recreation

Submitted to: Journal of Aquatic Plant Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/23/2020
Publication Date: 8/31/2021
Citation: Pratt, P.D., Moran, P.J., Pitcairn, M., Reddy, A.M., O'Brien, J. 2021. Biological control of invasive plants in California’s Delta: Past, present, and future. Journal of Aquatic Plant Management. 59s:55-66.

Interpretive Summary: Weeds disrupt many of the important functions of the Sacramento-San Joaquin River Delta, including restricting the amount of water available for farmers and public drinking water. Weed control efforts in the Delta usually involve the use of herbicides or machines that remove the plants. However, insects that attack and kill weeds in the Delta have also been used since the 1980s. The use of insects or pathogens to suppress weeds is called biological control. The USDA and other collaborating agencies have a long history of developing biological control tools for water managers and other stakeholders. In this article, we review the history of biological control in the Delta and update the reader on the current status of projects under development. We conclude that demand for biological control will increase in the coming years, with the increase in public scrutiny on the use of herbicides.

Technical Abstract: Implementation of weed biological control in the Sacramento-San Joaquin River Delta began in 1982 with the introduction of three water hyacinth natural enemies. The weevil Neochetina bruchi is widely distributed in the Delta, a second weevil is rare, and a moth failed to establish. Renewed interest led to the release of the water hyacinth planthopper Megamelus scutellaris, research on cold-hardy biotypes of the weevil Neochetina eichhorniae, the moth Niphograpta albiguttalis, the stem-mining flies Thrypticus spp., and the mite Orthogalumna terebrantis. Research has also recently expanded to target non-native water-primroses, including host range testing of a thrips (Liothirps ludwigi), surveys in South America for natural enemies, and the colonization of Tyloderma weevils in a containment laboratory. Research on Brazilian waterweed led to evaluating the leaf-mining fly Hydrellia egeriae and additional surveys in the plant’s native range. Biological control of Arundo donax has resulted in the release of a shoot-galling wasp, Tetramesa romana, and an armored scale, Rhizaspidiotus donacis. Both insects are established at locations upstream of the Delta and future prospects include the introduction of the leaf-mining midge (Lasioptera donacis). Alligatorweed was recently discovered in the Delta for the first time and efforts are underway to introduce the beetle Agasicles hygrophila and the thrips Amynothrips andersoni. Research on native insects to control exotic weeds, like the weevil Bagous lunatoides for South American spongeplant (Limnobium laevigatum), is also being considered. While weed suppression remains elusive, the importance of biological control in the Delta is expected to increase as stakeholders seek treatment alternatives.