Recipient Organization
UNIV OF WISCONSIN
21 N PARK ST STE 6401
MADISON,WI 53715-1218
Performing Department
RESEARCH & SPONSORED PROGRAMS
Non Technical Summary
Biological control - the use of predators and parasites to control agricultural pests - is often effective, stopping pest outbreaks without direct chemical control by farmers. A persisting question, however, is why biological control is very effective against some pests and in some crops, but relatively ineffective for others. The purpose of this study is to understand what makes biological control of pea aphids in alfalfa successful. This will shed light on how management practices in other crops might increase the effectiveness of biological control.
Animal Health Component
50%
Research Effort Categories
Basic
50%
Applied
50%
Developmental
(N/A)
Goals / Objectives
The planned research will investigate the role of multiple natural enemies in biological control, using pea aphid pests in alfalfa as a model system. For most agricultural pests, successful biocontrol involves multiple natural enemies. This complicates the problem of biocontrol, because understanding the long-term regulation of the pest requires understanding the dynamics of natural enemies that feed on resources other than the pest and often outside the crop or habitat in which the pest lives. Thus, in "open" agricultural systems in which natural enemies move in and out of fields containing a pest species, understanding long-term pest suppression requires studying the reproduction and dispersal of natural enemies across different fields, different crops, and possibly different habitats. The objective of the planned research is to understand the long-term, self-sustaining biocontrol of pea aphids in alfalfa brought about by multiple natural enemies moving broadly
throughout the landscape. Pea aphids are attacked by a specialist parasitoid, several aphid-specific predators (e.g., ladybird beetles), and several true generalist predators (e.g., nabids). All natural enemies are highly mobile, and all reproduce outside alfalfa fields. The planned research will take an explicitly population dynamical approach to understanding biocontrol, specifically investigating the density-dependent regulation of pea aphids caused when mortality from natural enemies increases as pea aphid densities increase. To investigate the long-term sustainability of biocontrol, the research will be conducted over multiple natural enemy generations, thereby incorporating the dynamics of the natural enemies. This project will address the fundamental question of what makes biocontrol in open systems successful.
Project Methods
The approach will involve very large (6x30 m) field cages and mathematical/statistical models to interpret the experimental data and predict the outcome of biocontrol beyond the spatial and temporal limits of the experiments. Successive experiments will incorporate successively greater levels of landscape complexity, thereby titering the amount of landscape complexity needed for successful biocontrol. Specifically, the first experiment will compare biocontrol within closed cages containing only alfalfa to biocontrol in "sham" cages that are open to the immigration of natural enemies from surrounding crops and habitats. This will reveal the importance of non-alfalfa sources of natural enemies for biocontrol. The second experiment will compare closed cages containing alfalfa, soybeans, and corn (the three major crops in southern Wisconsin) with open sham cages containing the same crops. This will reveal the importance of non-crop sources of natural enemies for biocontrol.
The third experiment will again use cages containing alfalfa, soybeans, and corn, but will close cages against immigration of natural enemies at different times, thereby producing a gradient in the time of exposure to outside natural enemies. The goal of these collective experiments is to find that point at which pest and natural dynamics within cages resemble those in open fields, and thereby identify the level of landscape complexity necessary for effective biocontrol. Understanding the success of biocontrol requires explicit consideration of population dynamics and the density-dependent response of natural enemies (either via behavioral responses or reproduction) to increases in pest populations. Therefore, mathematical models of population dynamics will be statistically fit to the data from the experiments. These will aid the analyses and interpretation of the experimental results. They will also be used to ask predictive, "what if" questions about biocontrol for situations that
cannot be addressed experimentally. For example, the models could be used to investigate the consequences of the removal of a specific natural enemy species on the success of biocontrol of pea aphids. The approach will tightly couple field experiments and statistical models to understand the broad-scale dynamics of pea aphids and their natural enemies.