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ARS Home » Pacific West Area » Albany, California » Western Regional Research Center » Invasive Species and Pollinator Health » Research » Publications at this Location » Publication #145666
Title: DO TISSUE CARBON AND NITROGEN LIMIT POPULATION GROWTH OF WEEVILS INTRODUCED TO CONTROL WATERHYACINTH AT A SITE IN THE SACRAMENTO-SAN JOAQUIN DELTA, CALIFORNIA?

Author
item Spencer, David
item Ksander, Gregory

Submitted to: Journal of Aquatic Plant Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2003
Publication Date: 1/1/2004
Citation: Spencer, D.F., Ksander, G.G. 2004. Do tissue carbon and nitrogen limit population growth of weevils introduced to control waterhyacinth at a site in the sacramento-san joaquin delta, california?. Journal of Aquatic Plant Management. 42(1):45-48.

Interpretive Summary: Water hyacinth is a serious problem in the Sacramento Delta. Two weevil species have been introduced as biological control agents. To date, they have not had long-term impact on water hyacinth abundance. Factors such as weather, disease, predators, and plant quality affect growth and reproduction of insects. The purpose of this study was to test the hypothesis that water hyacinth tissue nitrogen (N) was not sufficient to support weevil growth. Water hyacinth in Whiskey Slough (CA) were sampled at 2 to 3 week intervals in 1995 , 1996, and 1997. Leaf samples were analyzed for tissue N. Tissue N was greatest in the leaf blade, followed by the stem base, and leaf petioles. Leaf blade tissue N was higher in spring and somewhat reduced in late summer and winter. Tissue N levels for Delta water hyacinth in conjunction with a previous study relating weevil growth to tissue N indicates that tissue N should not limit growth of either weevil species. Because it grows better on plants with high N content and because it has a greater impact on the growth of high N plants, the chevroned water hyacinth weevil may be a more effective biological control agent in the Sacramento Delta.

Technical Abstract: Water hyacinth (Eichhornia crassipes (Mart.) Solms), is a serious problem in the Sacramento Delta. Two weevil species have been introduced as biological control agents. To date, they have not had long-term impact on water hyacinth abundance. Factors such as weather, disease, predators, and plant quality affect growth and reproduction of insect herbivores. The purpose of this study was to test the hypothesis that water hyacinth tissue N was not sufficient to support weevil growth and reproduction. Water hyacinth in Whiskey Slough were sampled at 2 to 3 week intervals in 1995, 1996, and 1997. Leaf samples were analyzed for tissue and N. Tissue N was greatest in the leaf lamina, followed by stem bases, and leaf petioles. Lamina tissue N was higher in spring and somewhat reduced in late summer and winter. The lamina C:N ratio was generally < 15 after mid-May. Comparing tissue N levels for Delta water hyacinth with a previous study relating weevil growth to tissue N indicates that tissue N should not limit growth and reproduction of either weevil species. Because it grows better on plants with high N content and because it has a greater impact on the growth of high N plants, N. bruchi may be a more effective biological control agent in the Sacramento Delta.