Exploiting plant genotypic diversity for sustainable insect pest management

Exploiting plant genotypic diversity for sustainable insect pest management

Summary

The purpose of this project is to investigate the potential utility of increasing crop genotypic diversity for insect pest management. Evidence from natural and agricultural systems suggests that increasing crop genotypic diversity with cultivar mixtures holds promise for controlling insect pests. This research is pursuing this strategy using soybean and soybean aphids as a model system and a combination of field and greenhouse experiments. Alternative methods of control are needed for soybean aphid, which has become the primary pest in soybeans. This project also aims to characterize the natural enemy community in soybeans in Pennsylvania and the Northeastern United States. The first year of field experiments and data collection have been completed, as has a portion of the outreach goals. Despite expectations of high soybean aphid populations in the first year of this project, aphids maintained low populations during the course of the season. Additional greenhouse experiments and outreach are planned for the upcoming year.

Objectives/Performance Targets

Objective 1: Compare the effects of genotypically diverse mixtures vs. single lines on plant growth and yield and on aphid population growth.

Objective 2: Compare the effects of genotypically diverse mixtures vs. single line monocultures on natural enemies of the soybean aphid.

Objective 3: Compare predation services provided by genotypically diverse mixtures vs. those provided by single lines.

Objective 4: Characterize the natural enemy community of soybeans in Central Pennsylvania

Objective 5: Transfer knowledge gained from Objectives 1-4 to growers, extension agents and members of the public.

Accomplishments/Milestones

Objective 1: During the first year of the project, work addressing the first objective primarily consisted of the completion of a large field experiment at Penn State’s Research Farm. Sixty plots of soybeans were planted in a randomized complete block design with six low diversity treatments consisting of single lines and six high diversity treatments consisting of five-line mixtures, each replicated five times. Over the course of the summer, soybean aphids were counted on ten plants per plot to monitor aphid populations. Due to time constraints, aphids were counted on five plants for the last two dates. Plot yield was assessed at the end of the season by harvesting 17.5 feet of two rows in each plot. Instead of simply harvesting machine-planted plants to measure plant biomass, fifteen seeds were hand planted in each plot at the beginning of the season and were harvested and weighed. Planting the seeds in this manner ensured that we knew the identity (genotype) of each plant.

Results from this first year of study suggest that diversity level did not affect aphid populations in each plot. Aphid populations were also consistently and unexpectedly low during the course of the season and never approached the economic threshold of 250 aphids/plant. Because of low aphid populations, we were unfortunately unable to test in the field the potential of genotypic diversity as a management tool under high pest pressure, which is the situation in which we hypothesize there will be the greatest potential for an effect of diversity.

One greenhouse experiment that compared aphid populations in high diversity pots of five plants of different lines (genotypes) to low diversity pots of five plants of the same line has been completed, but the data are still in the process of being analyzed. Further greenhouse experiments are planned for the upcoming spring and summer.

Objective 2: Natural enemy populations were sampled bi-weekly in the plots described above during the first year of this project. To sample foliar arthropods, we sweep netted two rows of the plot. This was repeated during both the day and the night to capture both day- and night-active foliar predators. Pitfall traps were used to sample ground predators. Identification of these natural enemies has been partially completed.

Objective 3: We measured predation services in the plots by caging single plants with cages constructed from tomato cages and no-see-um mesh. Ten aphids were added to each plant at the beginning of the predation experiment and aphids were counted after 7 and 14 days. The proposed research used three treatments within each plot: predator exclusion, sham cage and no cage control. This was significantly expanded during the actual experiment to also include a day-predation cage and a night-predation cage. These additional cages were raised and lowered every morning and night for the duration of experiment, exposing the aphids to either day- or night-active predators. This addition, coupled with the day and night sweep net samples, will help elucidate temporal dynamics of predation on the soybean aphid.

Sentinel aphids were also put in each plot to measure predation on two dates. On each date, two cards with three aphids apiece were placed in each plot during the morning and at night. We revisited cards several times to identify predators and quantify aphid predation by counting preyed-upon aphids.

Objective 4: Natural enemy information from the above experiment will be used to help characterize the natural enemy community in soybeans. In addition, we sampled natural enemy populations in soybean fields of three local growers with sweep nets, pan traps and pitfall traps bi-weekly. We also measured aphid populations, but aphid numbers, and therefore natural enemy populations, were extremely low. Similarly, the samples collected in the large experiment described in objective 1, specimens collected from local fields are still being identified.

Objective 5: Because this project is in its first year, work for this objective has been limited. However, the field experiment for objective 1 was part of a field day at Penn State’s Research Farm, and information about the project was shared with a diverse audience including growers, extension agents and industry representatives. Furthermore, updates were provided to cooperating growers when applicable and information and results will be shared when finalized.

Impacts and Contributions/Outcomes

Not applicable at this time. Current data is too preliminary or incomplete to properly address impacts and contributions/outcomes.

Collaborators: