Evaluation of Plant Composition and Strip Size on the Effectiveness of Native Plant Conservation Strips for Sustainable Enhancement of Beneficial Insect Communities
The goal of this project is to determine whether native flowering plots composed of a mixture of annual and perennial wildflowers will support beneficial insects earlier and remain established longer than those strips composed of only perennial or annual wildflowers. We also determined the response of beneficial insects to the size of wildflower plots. The 2010 growing season was the first year for the project testing the effects of combining annual and perennial wildflowers on supporting beneficial insects and was the second year for the project testing the size of wildflower plots. For both projects we collected insects in the flower plots using a vacuum (a reverse-flow leaf blower). We found that densities of both insect natural enemies and pollinators increase with wildflower plot size. In the size plot treatments we also measured the effect of flower plot size on the biological control of aphids and found that biological control of aphids increased with wildflower plot size.
In order to improve grower knowledge of beneficial insect identification and supporting those insects with the use of flowering plots, we held two field days this summer. At the field days we invited growers, extension agents, government employees, and anyone interested beneficial insect conservation to come learn about our project. We also gave out information to attendees on how to set up wildflower plantings and the governmental programs available to growers to help with establishment and maintenance costs of these plantings. The project team surveyed growers in attendance at the field days before and after the meetings, finding that their level of knowledge of conservation practices for building biodiversity in fruit farms increased after the training.
This research project has three main objectives: 1) determine whether native flowering plots composed of a mixture of annual and perennial wildflowers will support beneficial insects earlier and remain established longer than those strips composed of only perennial or annual wildflowers, 2) determine the response of beneficial insects to the size of wildflower plots, and 3) use our results to increase producer and public awareness of using native flowering plants to support beneficial insects in farmland.
Recent research at Michigan State University has identified and measured the relative attractiveness of native mid-western perennial flowering plants that can provide season-long floral resources for beneficial insects in agricultural landscapes. From their results, we have selected a set of herbaceous flowering plants that rank highly for their attractiveness to natural enemies and pollinators, and are listed under the Conservation Reserve Program – State Acres For Wildlife Enhancement (Table 1).
Wildflower seeds were sown in early spring 2009 and again in spring 2010 into plots that were prepared in fall 2008 adjacent to the crop fields. Grower cooperators were advised to mow their wildflower plots once a month during both years (alternating mowing half of the plot each month during 2010) to control annual weed growth and facilitate perennial wildflower establishment (Figure 1).
In the fall of 2009 we prepared twenty-four 6 x 6 ft plots at Trevor Nichols Research Complex (TNRC) in Fennville, Michigan. The twenty-four plots are made up of 4 flower treatments with 6 replicates each: control, perennial-only, annual-only, and a mix of both flower types. Each of the 6 control plots is 6 x 6 ft, and was treated in the fall of 2009 to control weeds. The perennial-only plots are each 6 x 3 ft plots of a blend of 15 perennial wildflowers that have bloom times that together span the spring-summer growing season (Table 1). The seeds were hand sown (38.5 ounces/acre) in mid-May 2010 and lightly raked in order to maximize soil-seed contact. The perennial sections of the plots were weed-whipped (5-cm height) once a month to prevent seed set by annual weed plants. The six annual-only plots are each 6 x 3 ft plots and were sown by hand with seeds of only buckwheat (Fagopyrum esculentum), which is a common flowering plant used in supporting beneficial insect. The six “mix” plots will be a 6 x 3 ft perennial flower section and a 6 x 3 ft annual flower section, representing the corresponding perennial-only and annual-only plots (Figure 1). The perennial sections and the annual sections of the mix plots were sown with the same corresponding seed blends and underwent the same seed sowing and weed control methods.
During bloom-period of the flowers (only buckwheat bloomed this first year) we vacuum sampled for three 30-second samples using a reverse-flow leaf blower with a fine mesh bag placed over the intake. Sampling was focused on the flowering portions of the plots, and collected samples were placed in a cooler and then frozen to kill and preserve the insects. Natural enemies, bees, and pest insects will be separated, identified to major taxonomic groups, and quantified in the laboratory for subsequent diversity and abundance analyses.
In the fall of 2008 we prepared twenty-five square plots at TNRC consisting of a logarithmic series of five size treatments with 5 replicates each: 1 m2, 3 m2, 10 m2, 30 m2, and 100 m2. These twenty-five plots are positioned within the field in a 15 m by 15 m grid with the center of each plot being in the center of a grid square (Figure 2). The plots are arranged within the grid using a Latin-square design in order to control for landscape variation. In order to improve establishment of flowers in mid-May of 2009, each of the plots were planted with plugs (seedlings) from 12 perennial wildflower species (Table 2), chosen from the 15 species used in the perennial-annual project. These flowers have bloom periods that span the months of May through October, and each plot contains equal ratio of plants from each of the 12 flower species. Once a month throughout the growing season, the number of blooms per 0.1m2 was measured by counting flowers in randomly selected 0.1m2 quadrats.
Although this is was the second year for this project, this was the first year that these different sized plots had flowering plants that bloomed, so we were able to sample the abundance of beneficial insects attracted to the twenty-five flowering. From June through September each of the twenty-five plots was vacuum sampled in a random order, once every month for four 30-second samples for each plot using a modified reversed-flow leaf blower with a fine white mesh bag placed over the intake. Negative control samples were taken from the grassy areas separating the different flower plots (Figure 2). Sampling was focused on the flowering portions of the plots, and collected samples were placed in a cooler and then frozen to kill and preserve the insects. Natural enemies, bees, and pest insects were separated, identified to major taxonomic groups, and quantified in the laboratory for subsequent diversity and abundance analyses.
In order to measure the effects of flower plot size on biological control, soybean plants were grown from seed in the greenhouse and transferred into 6 inch square pots. I placed two V6-stage soybean plants infested with a known mix of 10 (4 adult, 3 mid-instars, and 3 early instars) soybean aphids, Aphis glycines Matsumura (Hemiptera: Aphidae) into the near center of each of the twenty-five square plots for two weeks, with two replications – total of 50 covered plants and 50 uncovered plants. One of each soybean plant in each plot was completely covered – including the pot – with a fine, nylon mesh to exclude all natural enemies from the aphids, and the other soybean plant was left uncovered to allow for predation/parasitism of aphids (Figure 3).
The number of aphids per plant were counted after two weeks in mid-July and then again with another set of V6 soybean plants in August. Aphid population growth from the covered and uncovered trials will be used to extrapolate the effects of flower patch size on predation.
To relate biological control services to patch size, we calculated the relative aphid suppression found in each plot by expressing the change in aphid numbers on open and covered plants as a proportion of aphid abundance in the absence of predators for any given plot. The resulting Biocontrol Services Index (BSI) can vary from 0 to 1, with values increasing as the level of aphid predation increases (Gardiner et al. 2009). We found a significant increase in BSI with wildflower plot size (Figure 4), and looking at aphid abundance, there was a significant decrease in aphid abundance with plot size (Figure 5).
In order to improve producer and public awareness of using flowering plant diversity in farms to conserve beneficial insects including natural enemies and pollinators, we helped to organize two field days this summer – one in Sutton’s Bay, MI and one in Fennville, MI (Figure 6 – Not uploaded due to human participants). Grower collaborators, other growers, extension agents, government employees, and anyone interested in beneficial insect conservation were invited to the events to come learn about beneficial insects from a wildflower expert, NRCS and FSA staff, Dr. Rufus Isaacs, and his graduate student, Brett Blaauw. We also gave out information to attendees on how to establish and maintain wildflower plantings and the government programs available to growers to help with establishment and maintenance costs of these plantings. We also handed out information on current data and results that help advocate for the use of such beneficial insect conservation practices (Figures 8 and 9). The project team surveyed growers in attendance of the field days before and after the meetings to determine their level of knowledge of conservation practices for building biodiversity in fruit farms before and what they were able to learn from the meeting (Tables 3 and 4). After the meetings, attendees were 15-20% more likely to correctly identify beneficial insects.
- Figure 2. A.) An aerial photograph of the wildflower plantings at the Trevor Nichols Research Center showing the different sizes, 2010. B.) Ground level photographs of the different sized flower plots, 2010.
- Figure 4. Biocontrol services index (mean ± SEM) for the different sized plots. Plot sizes not connected by the same letter have a significantly different BSI (oneway analysis of variance, F4,40 = 5.62, p = 0.0011 followed by comparisons for each pair using Student’s t, a=0.05).
- Figure 5. Comparison of aphid numbers at the initial and final (two weeks later) (mean ± SEM) for the different sized plots. Plot sizes not connected by the same letter have a significantly different BSI (oneway analysis of variance, F5,44 = 56.4, p < 0.0001 followed by comparisons for each pair using Student’s t, a=0.05).
- Figure 8. Page 1 of an information pamphlet provided at the 2010 summer field days, which summarizes some of the early data from our project.
- Figure 9. Page 2 of an information pamphlet provided at the 2010 summer field days, which summarizes some of the early data from our project.
- Table 4. Questionnaire results taken at the 2010 summer field days showing an increase in ability of participants to correctly identify beneficial insects.
- Figure 3. The setup for measuring biological control of soybean aphids on soybean plants. A.) Soybean plant covered in mesh, protecting the aphids from predators, and B.) soybean plant without mesh, with aphid exposed to predators.
- Table 3. Summary of second year questionnaire results taken at the 2010 summer field days.
- Table 1.
- Figure 1. The picture shows an example of a flower plot with a perennial flower (mix of 15 species) side and an annual flower (buckwheat) side. During the first year there is considerable growth and flowering in the annual side, but we only saw vegetative growth on the perennial side.
- Table 2.
Impacts and Contributions/Outcomes
The first year of this multi-year project has been productive. We took numerous photographs of the flower plots over time (e.g. Figure 2B), as well as of the insects that visited the flowers in the plots (Figure 7). We collected many samples and are still processing much of them, but with the data we have analyzed we created pamphlets to share with growers at meetings (Figures 8 and 9), increasing the visibility of this project and insect conservation practices to growers across Michigan. The current results from this project, Response of Natural Enemies and Their Ecosystem Services to Wildflower Planting Size, were presented at the 2010 Entomological Society of America’s annual meeting in San Diego, CA (Figure 10). The poster received first place in the ESA’s Plant-Insect Ecosystems Section, Biological Control Group Student Poster Contest. We will continue to process our samples and to share our results with the participating growers and with others who are interested.
- Figure 7. Examples of beneficial insects observed visiting wildflowers in the size plots at Trevor Nichols Research Complex. A.) a hoverfly on yellow coneflower, B.) a bee on New England aster, C.) a lacewing larva feeding on an aphid on boneset, and D.) a beefly on a cup plant.
- Figure 10. Poster presented at the 2010 Entomological Society of America’s annual meeting in San Diego, CA.
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