Can Wild Bees Meet Pollination Needs in Apples?: Determining the Efficacy of Native Bees and Their Contribution to Pollination

Can Wild Bees Meet Pollination Needs in Apples?: Determining the Efficacy of Native Bees and Their Contribution to Pollination

Summary

To date, research on the SARE-funded project entitled, “Can wild bees meet pollination needs in apples?: Determining the efficacy of native bees and their contribution to pollination”, has 1) Documented the abundance and diversity of wild, native bees within approximately 22 apple orchards covering a large geographic region of Wisconsin over two field seasons, 2012 and 2013, and 2) Compared fruit set at orchards with and without managed honey bees, and at orchards with varying abundance and diversity of wild bees in both 2012 and 2013, and 3) Created an online guide to common, spring wild bees of the Upper Midwest. Furthermore, I have processed and analyzed data from the 2012 and 2013 field seasons, and I have begun writing a manuscript with that data. My research results show that wild bees are important contributors to apple pollination.  I have found that orchards with a high diversity of wild bees have a greater fruit set. Surprisingly, the contribution of honey bees to apple pollination is insignificant: fruit set is not higher at orchards that use honey bees, and fruit set does not increase with the number of honey bees at the orchard. These results highlight the significant role of wild bees in apple pollination, and suggest that growers could reduce costs associated with managing or renting honey bees by relying solely on wild bees for pollination. These research results were presented to apple growers at the 2013 and 2014 Wisconsin Fruit and Vegetable Conferences.

Objectives/Performance Targets

This research has three main objectives: (1) To assess which wild bees are most effective at pollinating apples, (2) To determine whether wild bees alone, and in what numbers, can provide full pollination for apples, and (3) To develop a field ID guide to effective apple pollinators.

Outputs from this research include presentations to apple growers at grower meetings and networks. Outputs also include a pollinator ID guide for both apple growers and the general public. Additionally, research results and the ID guide will be available online. Furthermore, this research will be presented to other scientists and conservation organizations at entomology and ecology conferences, and will be published in peer-reviewed articles.

Accomplishments/Milestones

Objective 1:  To address objective 1, we sampled wild bees at 21 apple orchards during the 2012 and 2013 growing seasons. Twenty of these orchards were sampled in both years. These study sites span a large portion of southern Wisconsin.  Previous research done in 2010 collected wild bees from 30 orchards across a similar geographic area. From these wild bee collections, we were able to assess which wild bee species are the most abundant and universal across all study sites.  Andrena nasonii is by far the most abundant species, accounting for approximately 1/3 of all bees collected.  The genus Andrena, which consists of ground-dwelling, spring-emerging bees, is also the most abundant genus.  These results were consistent across the three years of sampling despite some differences in the wild bee community composition. These research results inform predictions on the most effective wild bee pollinators of apples, as abundance is one key component of efficacy.

In this upcoming field season (April – May), we will measure different bee species’ fidelity to apples.  Fidelity can be analyzed by examining pollen loads for percent apple pollen versus other pollen. A bee species’ fidelity is an additional component that influences pollinator efficacy.  Combining research results on abundance, visitation rates, fidelity, and additionally incorporating previous research on pollen deposition rates, we can conclude which bee species are the most effective pollinators of apples.

Objective 2:  To address objective 2, during the 2012 and 2013 growing seasons, we compared fruit set at orchards with and without managed honey bees on site. Fruit set was measured on branches open to bee pollinators and on branches closed to all pollinators in order to measure the pollinator-dependency of apples. We also measured wild bee abundance and diversity, as well as honey bee abundance, during bloom at all study sites with bee bowl traps. In each year, approximately 8 sites without honey bees and 8 sites with honey bees were sampled. Fruit set on closed branches was less than 1%, but was approximately 11% on open branches, illustrating that apples are highly pollinator dependent. We found that the presence of honey bees at the orchard did not increase fruit set (Figure 1).  Furthermore, the number of honey bees captured in the orchard during bloom (an indication of honey bee abundance) was not related to fruit set (Figure 2). However, the species richness of wild bees was positively related to fruit set (Figure 3).

During the next three months (March – May), work for this objective will be focused on completing a manuscript highlighting these research results.  This manuscript will be published in a peer-reviewed journal.  Furthermore, research results will be presented to growers at the Fruit School in Door County WI in April.        

Objective 3:  Our work thus far on objective 3 has resulted in the completion of an online guide to common, spring wild bees of the Upper Midwest: http://energy.wisc.edu/bee-guide/.  This guide is interactive, and includes a picture-matching and dichotomous key option for identifying spring wild bees of Wisconsin and the neighboring states.  Research results from the 2010-2013 growing seasons informed our assessment of which wild bee species were relatively common.  Creating this online guide involved designing a layout, taking multiple, high resolution pictures of bee specimens with a camera-scope, editing pictures, and working with a web designer to achieve the final outcome.

In the future, we will work to make a hard-copy complement to this online guide.  While the hard-copy version will not be as interactive, or amenable to edits, it may be useful for growers with limited internet access.  Furthermore, we hope to design a similar guide for bees of the late summer and fall.  Apple growers are likely interested primarily in spring bees that pollinate their crops, but the general public may find a late-season bee guide helpful. 

• Figure 1
• Figure 2
• Figure 3

Impacts and Contributions/Outcomes

The stated goal of this project is to help growers determine the contributions of wild bees to the pollination of apples, thereby decreasing their dependence on honey bees.  Our research documents a number of wild bee species in apple orchards during bloom.  We have found that having a high diversity of wild bees will increase fruit set.  However, having managed honey bees at the orchard does not increase fruit set.  Furthermore, increasing the number of honey bees does not affect fruit set, suggesting that the benefits of bringing in more honey bees do not outweigh the rental and management costs.  We conclude that most orchards can achieve adequate fruit set with wild bees alone.  Our online guide to wild bee species that pollinate apples can help growers assess wild bee diversity, and make informed decisions regarding bee conservation. These results were presented to growers at the 2013 and 2014 Wisconsin Fruit and Vegetable Conference.  Research results were also presented at the 2012 and 2013 Entomology Society of America Meeting and the 2012 and 2013 Ecology Society of America Meeting.

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