- Agronomic: soybeans
- Crop Production: application rate management
- Education and Training: extension
- Pest Management: biological control, cultural control, genetic resistance, integrated pest management, prevention
Substantial evidence indicates that ecosystems benefit from increased diversity. For example, increases in plant species diversity typically lead to greater diversity of arthropod natural enemies, which in turn kill herbivores, limiting their damage and benefiting plant productivity. Unfortunately, modern agricultural monocultures tend to harbor minimal biodiversity and benefit little from complex ecological interactions associated with high diversity. Recent evidence, however, suggests that intraspecific (i.e., genotypic) diversity can be as valuable as plant species diversity in structuring arthropod communities and reducing herbivore populations. My research will pursue this tantalizingly simple strategy and assess the potential role of increasing genotypic diversity in crop fields to enhance predator diversity and abundance, reduce insect pests, and ultimately increase yield. Using soybeans as a model system, I will conduct field experiments to compare soybean aphid and natural enemy populations of low genotypic diversity to those of high diversity plots. Within this experiment, I will assess the strength of predation services between the two levels of diversity using predator-exclusion cages. Simultaneously, I will characterize the natural enemy community in soybean fields. This information is lacking for the Northeast and Pennsylvania, but is vital for understanding potential predation services. Results from both aspects of the project will be shared with growers and extension educators and will be integrated into outreach events. This will allow me to demonstrate the utility of genotypic diversity and natural enemies as sustainable methods of pest control to agricultural producers and educators and to members of the public at large.
Project objectives from proposal:
1. Compare the effects of genotypically diverse mixtures vs. single lines on plant growth and
yield and on aphid population growth.
As mentioned previously, plants can have “bottom-up effects” on insect herbivores. Some of
these bottom-up effects can be quantified through experiments that give aphids a choice
between cultivars and demonstrate aphid-preference and experiments that do not allow this
option, which illustrate a single cultivar’s effects on aphid population growth. Preliminary results
show the existence of these effects on soybean aphids, but further experiments are needed to
assess the cultivars chosen for this project. Measuring plant growth and yield will explore direct
impacts of aphids on plants and natural enemy effects mediated by their effects on aphid
2. Compare the effects of genotypically diverse mixtures vs. single line monocultures on natural
enemies of the soybean aphid.
Sampling the natural enemy populations in low and high diversity plots will help elucidate any
differences seen in aphid populations and plant measurements. Natural enemies from a
number of different guilds can exert strong “top-down control” of soybean aphids (Fox et al.
2004). I expect that increasing genotypic diversity will enhance these effects and that natural
enemy populations will be more diverse and robust in high diversity plots.
3. Compare predation services provided by genotypically diverse mixtures vs. those provide by
Objective 2 will provide a measure of the effects of increasing genotypic diversity on the natural
enemy community and help explain any effects seen on aphid populations. Another method is
to measure the actual service of pest suppression that they provide, which is the approach that
this objective takes. This incorporates all the potential effects of each natural enemy on aphid
populations and also includes any interactions, facilitative or disruptive, between natural
enemies and produces a simple measurement of the biological control service provided.
4. Characterize the natural enemy community of soybeans in Central Pennsylvania
Adopting and implementing a pest management strategy employing cultivar mixturesnecessitates understanding the natural enemy community and the biological control service they
supply. The natural enemy community in soybeans has been extensively characterized in the
Midwest, but information is sparse for the Northeast, where soybeans are still an important crop.
This knowledge is vital to manipulating the natural enemy community as part of an ecologically
sound management approach and has therefore been included as an objective in this project.
5. Transfer knowledge gained from Objectives 1-4 to growers, extension agents and members of
Disseminating results from the previous objectives is essential if genotypic diversity and its
effects on the natural enemy community are to become established as an attractive control
option for insect pests in any crop. If successful, providing growers with information from this
project will help catalyze the adoption of cultivar mixtures. More urgently, sharing my results
and the information I will gather is necessary to provide a control tactic that could be used to
manage the soybean aphid and to educate local growers on the technique.