Biological Control in Pest Management Systems of Plants (FY 2008)
If we can understand the mechanisms responsible for invasiveness we can learn how to disrupt those processes, leading to more effective management strategies. Despite increasing efforts and the development of a number of hypotheses, factors facilitating the success of invasive species remain unclear. It is becoming apparent that often several processes act together to cause invasiveness, necessitating a multidisciplinary approach, that unites multi-factorial experiments and analytical and simulation models to explore how factors interact. Surprisingly, such studies are scarce.We propose to work on hoary cress, Lepidium draba (Brassicaceae), a perennial rhizomatous mustard, native to Eurasia that invades crops, rangelands, and riparian areas in western North America, causing significant economic losses to U.S. agriculture. We have studied the
performance, competitive ability, and herbivorous insect communities associated with L. draba across Europe and the western U.S. at field sites and under standardized conditions over three years. We found that while L. draba performs better in the invaded range this is not due to evolution of increased competitive ability or release from generalist herbivores. The plant is, however, released from specialist herbivores and a number of these are currently studied as potential biocontrol agents. In addition, our results indicate that L. draba might experience reduced interspecific competition in its introduced range.We propose to conduct parallel manipulative experiments at six field sites, three in the native Eurasian and three in the introduced U.S. range of L. draba to answer the following questions:1)?To what degree does differential herbivore pressure in the introduced compared to the
native range contribute to invasiveness (enemy release hypothesis, ERH)?2)?To what degree does differential interspecific competition contribute to invasiveness (competitive release)?3)?To what degree do different management regimes and site characteristics, specifically cultivation, nutrient availability and grazing interact with herbivore pressure and/or competition?4)?Based on the findings of questions 1 to 3, we will develop population models simulating integrated weed management scenarios in an economic framework to identify the most ecologically and economically sound management strategy for different agricultural settings.This is to our knowledge the first attempt to compare the population biology of an invasive plant in its native and exotic range including experimental manipulations to establish cause-and-effect relationships between its abundance and different management
regimes and land uses. The resulting population models will allow us to simulate the cost-effectiveness of different management strategies. We will further be able to make predictions on the likely effectiveness of currently developed biological control agents prior to their release as well as their integration with other weed management tools.