The role of cover crop diversity on key generalist predator attraction and pest suppression

The role of cover crop diversity on key generalist predator attraction and pest suppression

Summary

Insect natural enemies play a critical role in suppressing agricultural pests through parasitism and predation, but they also rely on plants for alternative food and shelter when prey is scarce. Many agricultural landscapes are simplified and lack alternative plant resources. Natural enemy survival in these landscapes may be reduced because the resources on which they depend are scarce or absent. Addition of resource-producing insectary plants in the landscape represents a potentially effective tactic to promote natural enemies. These insectary plants may provide nutrient rich nectar and pollen to predators and parasitoids and may be able to be exploited to bolster the abundance of natural enemies and enhance their ability to suppress insect pests. Using cover crops as insectary plants to promote the presence of beneficial insects in the field represent a sustainable approach to pest management that can result in reduced reliance on pesticides which can safeguard grower health while providing other beneficial environmental services.

Objectives/Performance Targets

The specific objectives the study are:

1. 1. Evaluate the effects of resources from cover crops on the longevity and survival of two key generalist predators.

1. 1. Determine cover crop growth, development, and plant resource quality for two generalist predators

1. 1. Assess the foliar arthropod community associated with buckwheat, cowpea, and a buckwheat-cowpea biculture, compared to a fallow control.

1. 1. Monitor predation on prey insects within the cover crop strips and adjacent corn crop.

1. 1. Investigate dispersal of arthropods between the cover crop borders and cash crop plots.

Overall Progress:

In 2014, the field study, which included a weedy fallow, buckwheat monoculture, cowpea monoculture, buckwheat-cowpea biculture treatments, was planted in early June. Two weeks after planting, I initiated weekly assessments of insectary cover crops (Objective 2). I recorded establishment, plant density, height, leaf number, total number of buckwheat floral inflorescences and cowpea extrafloral nectaries and the presence of weed species. I also recorded climate data such as total accumulated degree days. Buckwheat established well and began budding four weeks after planting and continued through until termination. Cowpea establishment was more variable due to relatively poor germination. Cowpea plants were slower growing, relative to buckwheat, and therefore cowpea plots exhibited less ground coverage. Cowpea extrafloral nectaries were produced as expected and produced nectar. Biculture plots were generally dominated by buckwheat plants. The 2014 data on cover crop performance have been been entered and will be analyzed before the start of the 2015 growing season.

I initiated assessment of the insect community (Objective 3) via sweep net sampling four weeks after planting, when buckwheat began to bud. I took sweep net samples weekly in the cover crop borders until they were terminated approximately 7 weeks later. Within corn plots, I conducted weekly surveys to assess ladybeetle and minute pirate bug abundances. The samples are currently being identified, counted, and entered for analysis and interpretation.

To investigate the influence of the insectary cover crop treatments on predation in field (Objective 4), I placed bait European corn borer eggs, biweekly, in the cover crop borders and corn plots. The eggs were collected two days later and examined for evidence of predation and categorized accordingly. To date, all collected eggs have been examined, and the data have been recorded, entered and will be analyzed before the start of the 2015 growing season.

To monitor movement of arthropods between the cover crop borders and corn cash crop plots (Objective 5), the cover crop borders were marked with egg white protein and terminated after two days to allow sufficient time for arthropods to acquire the mark. Termination of the cover crops also served to “push” the insects into the corn cash crop. To later recover the protein-marked insects, I collected insects using yellow sticky traps and an insect aspirator. The collected samples were frozen, and will be processed using an enzyme linked imunosorbent assay (ELISA), and data will be analyzed and interpreted.

The greenhouse studies described in objective 1 have not yet been completed. I made two unsuccessful attempts to rear colonies of Coleomegilla maculata and Orius insidiosus using field-collected insects. I am currently gathering information to determine how to rear and maintain a stable colony.

Accomplishments/Milestones

Currently, the project is proceeding as expected and progress has been made in each of the objectives. These include assessing cover crop establishment and development, monitoring the insect community, and measuring predation levels and insect dispersal between the cover crop and cash crop, and completing training on an insect marking method. The results of the 2014 field season will inform activities in the 2015 field season. First, I will alter the seeding rate of buckwheat and cowpea in the monoculture and mixtures. While buckwheat grew vigorously, cowpea’s establishment was fairly patchy. This will be improved through a higher seeding rate in the cowpea monoculture. Because the biculture treatments were dominated by buckwheat, I plan to reduce the seeding rate of buckwheat and increase the rate of cowpea to produce a more even representation of the two species in the biculture. In addition, I’ve learned new strategies to implement when rearing insects and maintaining the colony. I successfully participated in training by Dr. James Hagler at the USDA Arid Land Agricultural Research Center on a protein marking method for tracking insect dispersal. The data collected this year will be formally analyzed and interpreted before the 2015 field season.

Impacts and Contributions/Outcomes

Results from this project were presented on several occasions. The first was a webinar via eXtension.org titled “Using Cover Crops to Achieve Multiple Goals on the Farm”, which focused on the benefits associated with cover crops for benefits ranging from managing soil fertility, weeds, insect pests, and promoting beneficial insects. The webinar attracted 360 people across the United States and Canada. Two audience members in particular, followed up by inviting members of our working group to further share our research and how it may be implemented on farms. Another grower, with specific interest in using flowering cover crops to promote pollinators and natural enemies in their field, expressed interest in inviting me to their farm for a field day to share the findings from some of my research. Findings from this work have also been shared at the annual meeting of the Entomological Society of America in Portland, OR, in an oral presentation entitled “Investigating the role of insectary plant diversification on attraction and pest suppression by the key predators in an insectary border”. I received a 1^st place award for this oral presentation.

While much of the research is still underway, positive reception of the research suggest that people are very interested in research that further explores the use of cover crops as insectaries to promote beneficial insects for pollination and pest insect suppression. Findings from this research can help to inform growers about specific cover crops that may be used in conjunction with other pest management tactics for more sustainable management of insect pests.

Collaborators: