Progress 10/01/08 to 10/01/11
Outputs
OUTPUTS: As we have demonstrated that both consumptive and non-consumptive effects of predators on prey are an important component of tri-trophic interactions for several insect herbivores, we have been investigating their importance for a major pest of NY potatoes, the Colorado potato beetle. We have investigated two questions. First, how do the non-consumptive effects of predators change damage by larval and adult Colorado potato beetles Second, how do predation and host plant quality interact to reduce feeding and plant damage by Colorado potato beetle larvae. This year we conducted an experiment to determine the fitness consequences of predation and host plant quality on Colorado potato beetle larvae. To manipulate the non-consumptive effects of predators on larvae we exposed larvae to Risk predators that could hunt but not kill by removing the last millimeter of the predator beak so it cannot pierce the insect cuticle. Host plant quality was manipulated using control potato plants (good quality) or potato plants treated with 0.5 mM jasmonic acid to induce plant defenses (low quality). Newly hatched Colorado potato beetle larvae were individually caged using vented transparency tubes onto stems of potato plants in the correct treatment. Every day, the instar of the beetle was recorded. Every three days, the beetle was weighed, leaf area eaten was measured and the stem was changed. Beetles were allowed to pupate and weighed three days after pupating. Adults were collected and a single male and female from the same treatment were caged and their egg production and longevity measured. Eggs from the adults were also hatched out and their responses to predation risk measured. PARTICIPANTS: Jennifer Thaler (PI) Scott Nelson, Research Support Specialist- operations manager All undergraduates helped collect the data. They also vetted the design of the project and were involved in data analysis as well as discussions of future research directions. Isa Betancourt, undergraduate student Ordom Huot, undergraduate student Jerry Shen, undergraduate student Marie Russell, undergraduate student TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
Colorado potato beetle feeding and growth were reduced by the presence of predators. Early in development, this effect was only detected for the beetles feeding on the high quality plants but later on there was also reduced feeding and growth on the low quality plants. We predicted that the beetles might increase their assimilation efficiency as a mechanism to compensate for reduced feeding but instead found that assimilation efficiency decreased in the predation risk treatment. Final pupal mass did not differ between treatments, likely because caterpillars in the predation risk treatments increased the length of the developmental period to allow more time for feeding. Adult mass upon emergence also did not differ between treatments. Surprisingly, the larvae of adults that had been exposed to predation risk grew more slowly than the offspring of control beetles. This indicates a strong within and across generation effect of predation risk. These results suggest that the behavioral responses to predation risk are strongest on high quality plants, and enhanced where sufficient nutrient levels are available to maintain growth in spite of reduced feeding. Also, predation risk alone has long-lasting effects on beetle performance indicating that even transient exposure to predators will have long-lasting effects on prey. This research would not have been possible without the support for a research support specialist and undergraduate research assistants provided by this grant.
Publications
- No publications reported this period
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Progress 10/01/09 to 09/30/10
Outputs
OUTPUTS: As we have demonstrated that both consumptive and non-consumptive effects of predators on prey are an important component of tri-trophic interactions for several insect herbivores, we have been investigating their importance for a major pest of NY potatoes, the Colorado potato beetle. We have investigated two questions. First, how do the non-consumptive effects of predators change damage by larval and adult Colorado potato beetles Second, how do predation and host plant quality interact to reduce feeding and plant damage by Colorado potato beetle larvae. We first tested the non-consumptive effects of the predator on Colorado potato beetle larvae and adults. To test the non-consumptive effects of predators on larvae we exposed larvae to Risk predators that could hunt but not kill by removing the last millimeter of the predator beak so it cannot pierce the insect cuticle. Herbivores were caged using translucent spun polyester sleeves onto individual potato plants with or without a Risk predator. After two days, beetles were weighed and leaf area measured. To test the effect of predation risk on adult Colorado potato beetles we caged individual potato plants and released a male and female stink bug onto half of the plant. The stinkbugs or were allowed to move on the plants for one day after which they were put in a mesh cage at the bottom of the plant. After the stinkbugs had been caged on the bottom of the plant, a single wild-collected female adult Colorado potato beetle was placed on the plant and leaf area consumption and eggs laid were measured every three days for a week. This design was used so that the stinkbugs could contact the plant and release odor cues into the bag but not physically contact the Colorado potato beetles. Visual cues were also blocked. In the second set of experiments, we exposed 3rd instar beetles to a stick bug predator (Podisus maculiventris) on tomato plants of high, medium and low quality for the beetles. The high quality plants do not express the jasmonate induced defenses (jasmonate-insensitive plants), wild-type plants have regular induced defenses and are medium quality, plants that constitutively express the jasmonate pathway (prosystemin) are poor quality. After rearing the beetle larvae on the three plant-types with or without predators for 3 days we measured the amount of leaf material eaten and weight gain. PARTICIPANTS: Ian Kaplan, postdoctoral researcher Isa Betancourt, Undergraduate student Scott Nelson, Resource Support Specialist TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Adult Colorado potato beetle feeding was strongly reduced by the presence of predators that could not contact them whereas larvae were not affected. Colorado potato beetle adults ate 45% less leaf material and this effect got stronger over the course of the 10 day measurement period. Adult oviposition was not affected by the presence of the predator. These results raise the exciting possibility of manipulating the adult beetle responses to predation as a means of reducing damage. Because adult beetles eat to produce eggs, reductions in feeding caused by the presence of predators may reduce subsequent egg production in a longer term experiment. Also, experiments testing for beetle preference may lead to fruitful avenues for manipulating adult host selection. We found that Colorado potato beetle larvae were equally consumed by stinkbug predators regardless of plant quality. The beetles ate more and grew more on the high quality plants but this did not affect predation rate. This research would not have been possible without the support for a research support specialist and undergraduate research assistants provided by this grant.
Publications
- No publications reported this period
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Progress 10/01/08 to 09/30/09
Outputs
OUTPUTS: This proposal aims to study ways to increase the effectiveness of native, generalist biological control agents of the Colorado potato beetle (CPB). Recent research demonstrates that predators not only kill prey (consumptive effects) but also "scare" prey (non-consumptive effects) and that this impact on prey behavior can account upwards of 50% of the reduction in plant damage caused by herbivores in the presence of predators. In addition, natural plant resistance traits have a strong impact on both the total effect of predators as well as the consumptive versus non-consumptive contributions. The primary goal of this project is thus to assess the total effect of a native predator, Podisus maculiventris (currently being an agent of "conservation biological control") and to partition it's effect into the consumptive and non-consumptive effects on potato cultivars differing in plant quality. The ultimate goal is to generate combinations of plant resistance and predators that are most effective at pest control. Treatments were established in 1 m3 breathable field cages to disentangle interactions between plant resistance and biological control and whether interactions are due to the consumptive or non-consumptive effects of the predator on prey. In field experiments, we establish treatments on 3 cultivars, one high quality, one medium and one low quality for CPB. The plant quality treatment was crossed with a predator or no predator treatment. In each replicate six 2nd instar CPB were caged either by themselves or with a predator (one adult P. maculiventris). After one week, we measured the number of CPB surviving, the amount of leaf area consumed and the weight of each surviving CPB larva. PARTICIPANTS: Jennifer Thaler Dr. Ian Kaplan (postdoctoral researcher) Elena Olsen (Cornell undergraduate research assistant) TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
We found that the effect of predators on CPB was affected by the quality of the plant. In the absence of predators, the CPB ate more leaf area on the high quality plants. The predators consumed the same number of CPB on all plant types. However, the response of the CPB to the predator differed according to plant type. The CPB ate less and gained less weight in the presence of the predator on the high and medium quality plants. On the low quality plants, they ate and gained the same weight irrespective of the presence of predators. This fits with predictions that herbivores will be more able to behaviorally defend themselves against predators by eating less when they are feeding on a nutritionally suitable plant. On poor quality plants, the herbivores cannot afford to stop eating in the presence of predators even though this can increase their vulnerability to predation. This has impacts on when these predators will be more effective biocontrol agents. This project could not have been completed without the postdoctoral associate (Dr. Ian Kaplan) and the undergraduate research assistant (Elena Olsen) who were instrumental in conducting the experiments.
Publications
- No publications reported this period
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