Native Plant Conservation Strips for Sustainable Pollination and Pest Control in Fruit Crops

Native Plant Conservation Strips for Sustainable Pollination and Pest Control in Fruit Crops

Summary

In spring 2011, the third year of this project, we sampled beneficial and pest insects within crop fields adjacent to the flower plots and those adjacent to mown grass field margins, finding significantly more beneficial insects in crop fields adjacent to wildflower plantings. Comparing results from the past three years we have found that the abundance of both pollinators and natural enemies increase while herbivorous insects did not change in crop fields adjacent to wildflower plantings, with significantly more of these beneficial insects being in crop fields adjacent to the wildflower plantings compared to those adjacent to a grass field margin. In order to determine the effects of wildflower plantings on pollination, we measured fruit yield in crop fields adjacent to the flower plots and those without flowering plots. After two years of establishment time, the third year of measurements we found a significant increase in percent fruit set and number of mature seeds in blueberry fields adjacent to the wildflower plantings. We used the average berry weight and percent fruit set to calculate an estimate of fruit yield, and although not statistically significant, the fruit yield was higher in blueberry fields adjacent to the wildflower plantings. In fields adjacent to wildflower plantings we also found an increase in biocontrol of corn earworm eggs (in blueberry) and of leafminer larvae (in apple) compared to crop fields adjacent to grass field margins.

In order to improve grower knowledge of beneficial insect identification and supporting those insects with the use of flowering plots, we presented at numerous extension meetings and conference during the past year. These presentations generally included information on beneficial insect identification and biology, establishment and maintenance of wildflower plantings, and current results from this ongoing project.

Objectives/Performance Targets

This research project has four main objectives: 1) increase pollination and reduce pest abundance in fruit crops by deploying native plant conservation strips to support native bees and natural enemies, 2) increase producer and public awareness of using flowering plant diversity in farms to support beneficial insects including natural enemies and pollinators, 3) improve producer knowledge of beneficial insect identification and biology, and 4) develop guidelines for increased implementation of insect conservation strips in farmland.

Accomplishments/Milestones

As with the previous two years, we continued to use a combination of observational sampling, vacuum sampling, yellow sticky cards, and pollination measurements to determine whether wildflower plantings lead to an increase in beneficial insect abundance and improved biological control and pollination services within adjacent crop fields compared to fields adjacent to grass field margins. We also added an experiment where we used corn earworm eggs to measure the biological control services in blueberry fields adjacent to wildflower plantings and fields adjacent to grass field margins.

To measure pollinator abundance during crop bloom, observations were made at each of the crop fields adjacent to the wildflower plantings and the grass field margins, recording the identity and number of flower-visiting insects (bees, flies, wasps, etc.). Compared to the 2009 results, in 2011 we observed a higher proportion of native bees visiting crop flowers (Figure 2). Comparing over a three-year period, the abundance of native bees has significantly increased over time in crop fields adjacent to wildflower plantings (Figure 3). Abundance and diversity of pollinators during crop bloom were further assessed in the fruit crops through vacuum sampling using a modified reversed-flow leaf blower. These samples are still being assessed.

To measure pollination levels in blueberry and apple, flower buds were tagged, counted, and then covered with a fine nylon mesh bag to exclude insect pollination. After bloom the number of fruit per bagged and open samples were counted to determine percent fruit set. Prior to harvest, fruit from tagged clusters at each location were collected and weighed to determine average percent fruit set, fruit weight, and number of mature seeds were counted as a measure of pollination success. Given time for the wildflowers to establish and for insects to inhabit theses areas, after the third year of this project we found a significant increase in percent fruit set and number of mature seeds in blueberry fields adjacent to the wildflower plantings (Figure 4). Average berry weight did not significantly differ between the two treatments, but there was a trend of larger berries being found in fields adjacent to wildflower plantings (Figure 4). The blueberry pollination data were used to calculate the estimated fruit yield for 2011. Although not statistically significant, the fruit yield was higher in blueberry fields adjacent to the wildflower plantings (Figure 5). It is expected that as the wildflower plantings continue to establish, the benefits observed will continue to increase. Even a slight increase in fruit yield may potentially cover the costs of establishing and maintaining these wildflower plantings.

The abundance and diversity of natural enemies and pest insects were determined in the fruit crops in each of the fields adjacent to the wildflower plantings and also those adjacent to grass field margins using observational and yellow sticky trap techniques. In 2011 we observed a diverse community of natural enemies in crop fields, which included ants, long-legged flies, and hoverflies (Figure 6). Comparing over a three-year period, the abundance of natural enemies has significantly increased over time in crop fields adjacent to wildflower plantings, and the abundance is significantly higher in fields adjacent to the plantings compared to fields adjacent to mown grass margins (Figure 7). In addition to these observations, we also sampled natural enemies within the crops using yellow sticky traps. These samples are still being assessed.

As a new experiment for the 2011 field season, during June, July, and August we used sentinel corn earworm eggs (Lepidoptera) as a prey item to determine how wildflower plantings affect biocontrol in crop fields. Although corn earworms are not pests of blueberries, eggs were killed by freezing to ensure they would not hatch and pose no threat to the crop. The eggs were glued onto cardstock squares and deployed at the five blueberry farms. Two egg cards were placed at three positions, in the wildflower planting, along the border of the crop field, and 15 m into the interior of the crop field. Egg cards were also placed at the three corresponding positions in crop fields adjacent to a grass field margin. We measured biocontrol services by comparing egg damage/removal before being placed into the field with the egg damage/removal after being in the field exposed to natural enemies for four days. The number of damaged or missing eggs was used to calculate the biocontrol services index (BSI; Gardiner et al. 2009). We calculated significantly higher BSI values and hence higher biocontrol for egg cards in the wildflower plantings and along the crop border adjacent to the wildflower plantings when compared to those in the corresponding positions in the grass field margin treatment (Figure 8.). Although it was not statistically significant, BSI for the crop interior positions was also higher in crop fields adjacent to wildflower plantings (Figure 8).

As another method to quantify the effect of wildflower plantings on biocontrol services, in the apple orchards we collected leaves infested with spotted tentiform leafminer larvae. Fifty infested leaves were collected from edge and interior rows in orchards adjacent to wildflower plantings as well as those adjacent to mown grass field margins. The infested leaves were dissected and assessed for the presence of parasitized larvae. We found a higher percent parasitism of leafminer larvae in infested leaves collected in orchards adjacent to the wildflower plantings (Figure 9).

In order to determine how pest insects respond to wildflower plantings, we also measured the community and abundance of insect herbivores in crop fields adjacent to wildflower plantings. In 2011 we found primarily Japanese beetles, leafminers, and aphids in blueberry fields (Figure 10). Comparing over a three-year period, the abundance of insect herbivores has not significantly changed over time in crop fields adjacent to wildflower plantings or in grass field margins (Figure 11). Although insect herbivores are still present, wildflower plantings do not increase herbivore abundance in crops fields.

Reference:
Gardiner, M. M., D. A. Landis, C. Gratton, C. D. DiFonzo, M. O’Neal, J. M. Chacon, M. T. Wayo, N. P. Schmidt, E. E. Mueller, and G. E. Heimpel. 2009. Landscape diversity enhances biological control of an introduced crop pest in the north-central USA. Ecological Applications 19: 143-154.

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 presented at numerous extension meetings and conferences during the past year. These presentations included information about using wildflower plantings to support beneficial insects and current results from this SARE funded project. In February 2012, Rufus Isaacs also presented results from this project to Michigan State Representatives at a Xerces Society sponsored pollinator conservation event.

The following are the authors, titles of presentations, and the meetings we presented results from this SARE funded project at:

Rufus Isaacs, Julianna Tuell, and Brett R. Blaauw. 2011. Habitat manipulation to support integrated crop pollination. Entomological Society of America Annual Meeting in Reno, NV. Oral presentation.

Brett R. Blaauw and Rufus Isaacs. 2011. How does wildflower planting size affect insect pollinators and their delivery of pollination ecosystem services? Entomological Society of America Annual Meeting in Reno, NV. Oral presentation.

Brett R. Blaauw and Rufus Isaacs. 2011. Variation in natural enemies and biological control with the size of native wildflower plantings. Royal Entomological Society – Ento’11 in Chatham, UK. Oral presentation.

Brett R. Blaauw and Rufus Isaacs. 2011. Response of natural enemies and their ecosystem services to wildflower patch size. Entomological Society of America – North Central Branch Annual Meeting in Minneapolis, MN. Oral presentation.

Rufus Isaacs, Julianna Tuell, and Brett R. Blaauw. 2011. Integrated Pollinator Management. Van Buren Conservation District’s Farming for the Future workshop, Paw Paw, MI. Oral presentation co-author.

Brett R. Blaauw and Rufus Isaacs. 2011. Enhancing Natural Enemies in Crops Using Flowering Plants. Great Lakes Fruit, Vegetable and Farm Market EXPO in Grand Rapids, MI. Invited oral presentation.

Brett R. Blaauw and Rufus Isaacs. 2011. Conserving Native Bees in Blueberry and Other Small Fruit. Great Lakes Fruit, Vegetable and Farm Market EXPO in Grand Rapids, MI. Invited oral presentation.

Brett R. Blaauw and Rufus Isaacs. 2012. The use of wildflower plantings to conserve beneficial insects in Michigan tree fruit. Northwest Michigan Orchard and Vineyard Show, Acme, MI.

Brett R. Blaauw and Rufus Isaacs. 2012. The effect of native wildflower planting size on beneficial insects and their ecosystem services. Science, Practice & Art of Restoring Ecosystems Conference, East Lansing, MI.

During the third year of this project, to help improve producer knowledge of beneficial insect identification and biology, we presented at numerous extension meetings. These presentations included a brief introduction to the identification of beneficial insects and the resources these insects need to thrive in agricultural settings. We also handed out an updated two-page beneficial insects guide that outlines some of the most beneficial and common natural enemies and pollinators that growers are likely to detect at their farms.

In order to develop guidelines for increasing implementation of wildflower plantings for the conservation of beneficial insects in farmlands we have taken extensive notes on the continuing processes used in establishing maintaining wildflower plots at our farm sites. Establishing wildflower plantings can be an expensive undertaking, so it is very important that we understand costs and benefits before we can best guide growers in adopting this conservation strategy. To make sure our guidelines are clear and remain affordable for growers we also distributed questionnaires to our grower cooperators to determine how much of their time and money was put into helping us establish and maintain the wildflower plantings.

We also created a short video entitled, “A Quick Guide to Establishing Wildflower Plantings for the Conservation of Beneficial Insects,” to give growers an introduction to the benefits, establishment, and maintenance of wildflower plantings to conserve beneficial insects. The video is posted on the Isaacs Lab webpage – http://www.isaacslab.ent.msu.edu/Videos.html

• Figure 11. The abundance of insect herbivores did not increase in blueberry bushes over time in crop fields adjacent to wildflower plantings.
• Figure 6. Top ten most abundant natural enemies observed in blueberry fields in 2011. Total number of observed natural enemies was 1,821.
• Figure 9. Parasitism of leafminer larvae in apple orchards was higher in trees adjacent to wildflower plantings.
• Figure 5. In 2011, estimated blueberry yield was higher in blueberry fields adjacent to flower plantings.
• Figure 2. Observed pollinator community. The proportion of native bees observed visiting crop flowers in blueberry fields has increased since 2009.
• Figure 7. The abundance of natural enemies observed in blueberry bushes throughout the growing season increased over time in crop fields adjacent to wildflower plantings.
• Figure 8. Biocontrol of corn earworm eggs was higher in wildflower plantings and in blueberry fields adjacent to wildflower plantings.
• Figure 10. Top ten most abundant insect herbivores observed in blueberry fields in 2011. Total number of observed herbivores was 1,408.
• Figure 3. The abundance of native bees observed visiting blueberry flowers during bloom increased over time in fields adjacent to wildflower plantings.
• Beneficial Insect Guide
• Figure 1. Wildflower establishment over a three year period.
• Figure 4. In 2011 there was a higher increase in pollination in blueberry fields adjacent to wildflower plantings as indicated by an increase in percent fruit set and average berry weight due to insect pollination.
• A Quick Guide to Establishing Wildflower Plantings for the Conservation of Beneficial Insects

Impacts and Contributions/Outcomes

After completing three years of this project giving time for wildflowers to grow and establish in the wildflower plantings, we now have data and results that appear to support our objectives. Our data show that the abundance of beneficial insects increases in crop fields adjacent to wildflower plantings over time. Our data also show that that after three years, pollination was higher in blueberry fields adjacent to wildflower plantings compared to fields adjacent to mowed grass margins. This increase in pollination led to a subsequent increase in average fruit yield at the blueberry sites. This year we also continued our good relationships and communication with our grower cooperators, and distributed information about our project and its objectives to local growers and the public through presentations and informational handouts. Convinced by the early results from this project, one of our apple grower cooperators has began work on establishing another wildflower planting at his farm.

As a way of increasing exposure of our project and spreading information and sources on insect conservation, we created a project sign for our grower cooperators (Figure 12). These signs are displayed near or within the wildflower plantings, so that visitors to the farms can get an introduction to this SARE funded project. We also had an article featured in the January issue of the Fruit Growers News – http://fruitgrowersnews.com/index.php/magazine/article/using-habitat-to-increase-pollination/ – that gave a brief description of our project and how to conserve pollinators using wildflower plantings.

• Figure 12. Example of an informational project sign placed at wildflower plantings and designed for our grower cooperators as an introduction to the project for visitors to the farm.

Collaborators: