Grantee Research Project Results
1999 Progress Report: Biocontrol by Native Generalist Predators: A Strategy for Reducing Pesticide Use in Vegetable Production
EPA Grant Number: R826099Title: Biocontrol by Native Generalist Predators: A Strategy for Reducing Pesticide Use in Vegetable Production
Investigators: Wise, David H.
Institution: University of Kentucky
EPA Project Officer: Hahn, Intaek
Project Period: October 1, 1997 through September 30, 2000
Project Period Covered by this Report: October 1, 1998 through September 30, 1999
Project Amount: $147,133
RFA: Exploratory Research - Environmental Biology (1997) RFA Text | Recipients Lists
Research Category: Biology/Life Sciences , Aquatic Ecosystems
Objective:
Results reported in the Year 1 Progress Report confirmed the hypothesis that predation by carabids and lycosids can decrease some insect pests of cucurbits to levels low enough to substantially elevate cucurbit productivity. This result suggested that farming techniques and habitat management programs that enhance densities of carabids and lycosids could reduce reliance upon chemical insecticides to control cucurbit pests. The results also clearly indicate that lycosids alone do not always benefit cucurbit production, because summer squash gardens allowing lycosids, but not carabids, to immigrate into the gardens harmed squash production. Patterns in the data led us to hypothesize that this unexpected result was caused by lycosids preying upon a major predator of squash bugs.Implementation of farming techniques that enhance densities of lycosids and carabids, and that decrease the rate at which lycosids prey on the predators of squash bugs, should increase the biocontrol effectiveness of lycosids and carabids in cucurbit production. Changes in alternative prey have the potential to cause these changes. Both carabids and lycosids prey heavily upon Collembola and other detritivores. An elevation in detritivore densities should: (1) reduce the rate of emigration of carabids and wolf spiders from gardens, (2) improve their rate of egg production, and (3) increase their survival by reducing rates of cannibalism and intraguild predation. Because many detritivores are high-quality prey, lycosids also should respond to increased densities of detritivores by decreasing the proportion of other predators in their diets. These arguments lead directly to the hypothesis that implementing a farming technique that increases Collembola numbers also will increase densities of carabids and lycosids, thereby increasing predation pressure on insect pests; and second, will cause lycosids to decrease their rate of feeding on other predators. Both responses would enhance the biocontrol effectiveness of carabids and lycosids. The field experiment conducted this past year was designed to test this hypothesis.
Progress Summary:
We attempted to increase detritivore densities in replicated (n=4) gardens by adding a commercially available shredded organic mulch (Creech Mulch, produced by Creech Services, Inc., Lexington, Kentucky) that is a composted mixture of 95 percent straw and 5 percent horse manure. This high-quality detritus was added to inter-row spaces in layers 50cm wide and 10cm thick along the entire row, immediately after spring tilling and before the application of straw. This addition was done in unfenced ("Open-Detrital") plots and two types of fenced treatments (described below). An unfenced control ("Open-Ambient") was also established. The two unfenced treatments made it possible to: (1) estimate the extent to which increased numbers of detritivores decrease rates of emigration of generalist predators; and (2) assess the naturalness of the fenced experimental plots, which were needed to test specifically for an effect of the detrital subsidy on trophic cascades. Because adding detritus could increase crop yield not only by increasing the density of predators that prey on insect pests, but also by adding nutrients to the soil, we designed the field experiment to separate effects due to these distinctly different interaction pathways by including two ("Ambient" and "Detrital") fenced predator-removal ("Enclosure-Removal") treatments. Because the effect of reducing predators has to be compared to another fenced treatment, the experimental design also included two fenced plots to which immigrating carabids and spiders were introduced: "Enclosure-Stocked- Ambient", to which predators were added at the normal immigration rate; and "Enclosure- Stocked-Detrital", to which predators were added at a rate 2-3x that of the ambient treatment, in order to mimic the anticipated effect of added detritus in the Open-Detrital treatment. Thus, the design of the 1999 study allows us to test directly for a predator-induced trophic cascade affecting vegetable production, as in the previous year. The major innovation of this expanded experimental design is the ability to determine the extent to which a detrital subsidy enhances the strength of this cascade.Plot sizes, planting procedures, methods for manipulating carabid and lycosid densities, techniques for sampling pests and other predators, and methods for measuring cucurbit production were the same as in the Year 1 experiment.
Only preliminary results are available at this time because nearly continuous field work has left no time to sort samples of detritivores and insect pests, or to analyze the data on cucumber production (squash have not yet been harvested). However, we have analyzed the effects of treatments on predator densities. The results are very satisfying because they confirm the hypothesis that adding high-quality detritus should elevate densities of carabids and spiders. Furthermore, we will be able to determine the mechanisms responsible for any effects on crop productivity that might result from such a response because: (1) densities of predators in the fenced enclosure-stocked plots (Ambient and Detrital) are comparable to densities in the more natural, less manipulated, open plots (Ambient and Detrital); and (2) our removal techniques extensively reduced numbers of carabids and spiders in the fenced enclosure-removal plots (Ambient and Detrital). Data collected from the last 3 weeks in September have not yet been analyzed.
Microcosm experiments conducted in the greenhouse with different types of substrate indicate that the elevated densities of predators in the field experiment are not simple behavioral responses to the added detritus, and thus likely reflect a response to elevated densities of detritivores and fungivores in the Detrital plots. Analysis of samples collected during the field experiment will confirm this interpretation and also will reveal the extent to which elevated predator densities caused a decrease in pest numbers.
Future Activities:
1. Completion of the 1999 field experiment that will involve taking final field samples in October, sorting samples during the fall and winter, analyzing the data, and manuscript preparation.
The other following planned activities for the next reporting period are designed to elucidate mechanisms causing the patterns that have been observed to date, and that will likely emerge once samples have been sorted and data analyzed from the 1999 field experiment.
2. Laboratory Microcosm Experiments. These will continue as outlined in the proposal, but their scope will be expanded considerably to: (1) understand in more detail the manner in which lycosids interfere with the impact of other predators on insect pests; and (2) determine how the abundance of alternative prey from the detrital food web affects rates of predation by carabids and lycosids on insect pests and other predators. Information from these microcosm studies will contribute to developing management strategies to maximize the beneficial effects of carabids and lycosids in pest control. Both types of microcosm studies will complement the field experiments, directly aiding in their interpretation.
3. Stable Isotope Analysis of Food Web Structure and Trophic Connections. Field samples of prey and predators have been collected, and more will be collected during the coming weeks, to determine whether analysis of stable isotopes of carbon, and particularly nitrogen, will reveal the relative extents to which predators are consuming prey from detrital and grazing food webs; and the effective number of trophic levels among the generalist predator guild. This technique of food-web analysis is relatively new; a recent publication in Ecology with a detrital food web of the forest-floor suggests that it can be applied profitably to the system.
4. Field Mesocosm Experiments. Depending upon the results obtained from the 1999 field experiment, and the availability of personnel, small-scale mesocosm experiments in the field will be planned to investigate mechanisms underlying interactions uncovered in this year's field experiment and to expand to a more natural setting promising results obtained in the laboratory experiments under number 2 above.
Denise McNabb will pursue research in number 3 and conduct some laboratory studies under number 2 for her M.S. thesis research. Juraj Halaj will work on numbers 1 and 4, and will assist Ms. McNabb with the stable isotope research. Dr. Andreas Lang, who recently completed his Ph.D. at the Ludwig Maximilians University in Munich, studying the impact of carabids and lycosids on cereal pests, applied for a Alexander von Humboldt postdoctoral fellowship, and will learn the status of his application in October. If his application is successful, Dr. Lang will join my research group in January 2000 and will conduct studies under goals number 2 and 4 above. The Alexander von Humboldt Foundation and the University of Kentucky will pay Dr. Lang's stipend and travel to the United States.
Journal Articles on this Report : 4 Displayed | Download in RIS Format
Other project views: | All 5 publications | 4 publications in selected types | All 4 journal articles |
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Snyder WE, Wise DH. Predator interference and the establishment of generalist predator populations for biocontrol. Biological Control 1999;15(3):283-292. |
R826099 (1999) |
Exit |
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Snyder WE, Wise DH. Antipredator behavior of spotted cucumber beetles (Coleoptera: Chrysomelidae) in response to predators that pose varying risks. Environmental Entomology 2000;29(1):35-42. |
R826099 (1999) |
Exit Exit |
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Snyder WE, Wise DH. Contrasting trophic cascades generated by a community of generalist predators. Ecology 2001;82(6):1571-1583. |
R826099 (1999) |
Exit Exit |
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Wise DH, Snyder WE, Tuntibunpakul P, Halaj J. Spiders in decomposition food webs of agroecosystems: theory and evidence. Journal of Arachnology 1999;27(1):363-370. |
R826099 (1999) |
Exit Exit Exit |
Supplemental Keywords:
biological control., RFA, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Ecosystem/Assessment/Indicators, Ecosystem Protection, exploratory research environmental biology, Ecological Effects - Environmental Exposure & Risk, Biochemistry, Ecology and Ecosystems, Agronomy, Ecological Indicators, pesticides, biocontrol, pest control, wolf spiders, conservation, native generalist predators, insecticides, vegetable production, agrochemcial, agriculture ecosystemsRelevant Websites:
http://www.uky.edu/~dhwise/wise.htmlProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.