Progress 10/01/05 to 09/30/06
Outputs
Progress Report 4d Progress report. This report serves to document research conducted under a Reimbursable Agreement between ARS and the California Department of Boating and Waterways. Additional details of this research can be found in the report for the parent project 5325-22000-019-00D, Biologically-Based Integrated Management of Invasive Aquatic & Riparian Weeds. Waterhyacinth (Eichhornia crassipes (Mart.) Solms), is a serious problem in the Sacramento-San Joaquin Delta infesting hundreds of miles of waterways. Scientists at the Davis worksite of the Exotic and Invasive Weeds Research Unit tested the hypothesis that plant quality might be altered and thereby increase feeding by the host-specific weevil Neochetina bruchi. Replicated field plots were amended with fertilizer and weevils were introduced and their feeding monitored along with plant growth characteristics. Results of two years of study, showed little differences between fertilizer levels and feeding
frequency and leaf- blade quality (nitrogen content). However, a small but significant reduction in average plant stature (petiolar height) was observed in plots where N. bruchi was released. However, additional studies suggested that this weevil was not optimally suited to produce adequate populations numbers during the period when water hyacinth grows most rapidly. It was felt that this was due to weather conditions (temperature and humidity) that were different than the site of origin for this insect natural enemy. Such information will be useful to local aquatic system managers in adjusting their control actions. Additionally, other studies were conducted to determine feeding responses to altered plant-leaf quality. This study was completed using replicated 3.1 by 3.1 meter quadrats that were inoculated with watehyacinth and N. bruchi in sites within the Sacramento-San Joaquin Delta. Measurement of plant growth rates, weevil feeding and presence of various stages of the
life-cycle (adults, eggs, instars, larvae) were determined. Ambient temperature and humidity were monitored. Results will provide a better understanding of what is limiting the efficacy of this insect, but suggest that either very large numbers need to be released annually, or a better-suited host-specific insect should be developed for use.
Impacts
(N/A)
Publications
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Progress 04/01/03 to 03/31/06
Outputs
Progress Report Objectives (from AD-416) To determine the influence of water fertility (augmented major nutrients) and host-plant quality (waterhyacinth) on herbivory and efficacy of Neochetina bruchi, an introduced weevil, in replicated release sites in the Sacramento/San Joaquin Delta. Impacts of weevil herbivory will be determined as well as reproductive responses (fecundity) to altered leaf tissue quality (primarily nitrogen and phosphorous levels). Plant quality in other sites will be assessed to determine if host plants provide adequate nutrition for rapid production of N. bruchi. Approach (from AD-416) Replicated 10m by 10m PVC quadrats will be inoculated with waterhyacinth in sites where N. bruchi isn't found. Quadrats will be suspended in an isolated slough the water just below will be augmented with 2x or 3x ambient levels of NPK using slow-release fertilizer, or un-augmented. In half the quadrats N. bruchi will be released (200 to 300 per quadrat). Bi-weekly observations and monthly sampling will determine levels of herbivory (petiole feeding scars), physical conditions (nutrients in water) and C-H-N in plants. Representative, destructive sub-samples will be taken from each quadrat at the end of the season (November) and number and type of weevil life stages will be determined. Samples of potential predators on N. bruchi will be sampled and gut contents examined. Comparisons of tissue quality, nutrients, weevil production, herbivory and efficacy (damage) will be analyzed via multivariate ANOVA. Studies will continue for three years. Documents reimbursable with CA Department of Boating and Waterways. Significant Activities that Support Special Target Populations This report serves to document research conducted under a Reimbursable Agreement between ARS and the California Department of Boating and Waterways. Additional details of this research can be found in the report for the parent project 5325-22000-019-00D, Biologically-Based Integrated Management of Invasive Aquatic & Riparian Weeds. Waterhyacinth (Eichhornia crassipes (Mart.) Solms), is a serious problem in the Sacramento-San Joaquin Delta infesting hundreds of miles of waterways. This study tested the hypothesis that plant quality might be altered and thereby increase feeding by the host-specific weevil Neochetina bruchi. Replicated field plots were amended with fertilizer and weevils were introduced and their feeding monitored along with plant growth characteristics. Results of the second year, as in the first year, showed little differences between fertilizer levels and feeding frequency and leaf-blade quality (nitrogen content). A small but significant reduction in average plant stature (petiolar height) was observed in plots where N. bruchi released. Follow-up observations at the study site two years after the last weevil introduction showed that there was no apparent impact on coverage of water surface by water hyacinth, even though weevils were still present. These results strongly suggest that the current populations of N. bruchi will not be adequate to significantly reduce the impacts of water hyacinth. As weather (temperature and humidity) suggest that this weevil is not optimally suited to produce adequate population numbers during the period when water hyacinth grows most rapidly.
Impacts
(N/A)
Publications
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Progress 10/01/04 to 09/30/05
Outputs
4d Progress report. This report serves to document research conducted under a Reimbursable Agreement between ARS and the California Department of Boating and Waterways. Additional details of this research can be found in the report for the parent project 5325-22000-018-00D, Biologically-Based Integrated Management of Invasive Aquatic & Riparian Weeds. To determine feeding responses to altered plant-leaf quality, replicated 3.1 by 3.1 meter quadrats were inoculated with watehyacinth and N. bruchi in sites within the Sacramento-San Joaquin Delta. During the second year, plants were inoculated earlier and nutrients were dispersed in a 25- point array compared to a 9-point array in the first year in order to provide more uniform exposures. Weevils and plants increased, but only a slight reduction in plant stature was observed by the second harvest period. Temperature and humidity were monitored within the plant canopy and these data suggest that the canopy provides
some buffering capacity against extreme shifts. However, the late-emergence and maturation of weevils (compared to rapid spring plant growth) probably limit the ability of the weevils to reduce plant biomass or areal coverage. A report was made available to the Ca. Dept. of Boating and Waterways.
Impacts
(N/A)
Publications
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Progress 10/01/03 to 09/30/04
Outputs
4. What were the most significant accomplishments this past year? This report serves to document research conducted under a Reimbursable Agreement between ARS and the California Department of Boating and Waterways. Additional details of this research can be found in the report for the parent project 5325-22000-018-00D, Biologically-Based Integrated Management of Invasive Aquatic & Riparian Weeds. A. Single Most Significant Accomplishment during FY 2004. Waterhyacinth (Eichhornia crassipes (Mart.) Solms), is a serious problem in the Sacramento-San Joaquin Delta infesting hundreds of miles of waterways. This study tested the hypothesis that plant quality might be altered and thereby increase feeding by the host-specific weevil Neochetina bruchi. Replicated field plots were amended with fertilizer and weevils were introduced and their feeding monitored along with plant growth characteristics. Results of the first year (of a three year project) indicated little
differences between fertilizer levels and feeding frequency and leaf-blade quality (nitrogen content), and thus have prompted revisions for the second year in which fertilizer amendments were elevated to document potential impacts for future biological control implementation efforts. B. None C. None D. Progress Report. To determine feeding responses to altered plant-leaf quality, eplicated 3. 1 by 3.1 meter quadrats were inoculated with watehyacinth and N. bruchi in sites within the Sacramento-San Joaquin Delta. Measurement of plant growth rates, weevil feeding and presence of various stages of the life- cycle (adults, eggs, instars, larvae) were determined. Ambient temperature and humidity is currently being monitored. During the second year, plants were inoculated earlier and nutrients were dispersed in a 25- point array compared to a 9-point array in the first year in order to provide more uniform exposures. Results will provide a better understanding of what is limiting the
efficacy of this insect.
Impacts
(N/A)
Publications
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