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

Project Overview

GNC10-142
Project Type: Graduate Student
Funds awarded in 2010: $9,850.00
Projected End Date: 12/31/2014
Grant Recipient: University of Wisconsin
Region: North Central
State: Wisconsin
Graduate Student:
Faculty Advisor:
Claudio Gratton
University of Wisconsin, Dept. Entomology

Annual Reports

Commodities

  • Fruits: apples, cherries, general tree fruits

Practices

  • Education and Training: on-farm/ranch research
  • Natural Resources/Environment: biodiversity, wildlife

    Abstract:

    We documented native, wild bees of apple orchards, examined their pollination contribution, and observed bee foraging behaviors. We found 80 species of native, wild bees within orchards; bumble bees and mining bees were most abundant.  Using managed honey bees did not increase apple fruit set in Wisconsin.  However, the number of wild bee species was positively correlated to fruit set. Wild bees showed foraging behaviors of more effective pollinators as compared to honey bees. We conclude that most growers can rely solely on native, wild bees for pollination. Additionally, this research project developed an online guide to identifying Wisconsin’s bees.

    Introduction:

    Insect-mediated pollination is essential for adequate apple yields (Delaplane and Mayer 2000)Historically many growers have relied on honey bees for apple pollination (Parker et al 1987).  However, due to declining numbers of honey bee colonies in the USA (Committee on the Status of Pollinators in North America 2007) and associated increases in hive rental costs, many growers are reducing the numbers of hives they manage or rent (Mallinger, unpublished data).  These growers hope they can obtain adequate pollination by relying on the activity of wild bees, but recognize they are incurring risks that yields will be lower without managed pollinators.  In general, there is little information on whether wild bees can fully pollinate apples in the Midwest.

    Using wild bees may be an effective alternative to honey bees.  Because of their behavior and biology, wild bees may be more efficient pollinators of apples compared to honey bees;  wild bees intentionally collect pollen while some honey bees collect only nectar, avoiding pollen in a behavior called ‘nectar robbing’ (Delaplane and Mayer 2000).   Wild bees are also more active in cooler and inclement weather and deposit more pollen on apple blossoms compared to honey bees (Boyle and Philogene 1983, Vicens and Bosch 2000, Thomson and Goodell 2001).  Yet, while guidelines have been developed for the number of honey bee hives per acre of apples needed to achieve full fruit set, no similar information exists on the numbers or types of wild bees needed for sufficient pollination.  Growers often have only anecdotal information on what native bees are found in and around their orchards and cannot make an informed decision about the extent of native bee activity on their farms.  This project will address the question of whether wild bees can provide adequate pollination of apples and will determine which native pollinators are most effective at pollinating apples.  In addition, this project will develop some tools necessary for growers to evaluate the wild bee community on their farms.

    Wild bees have been shown to fully pollinate other crops when they are abundant and diverse.  Studies in watermelon fields in eastern USA have demonstrated that these crops can receive full pollination by wild bees alone (Winfree et al 2007).  However, in Canada, it was determined that wild bees were not abundant enough to provide adequate apple pollination (Scott-Dupree and Winston 1987).  As pollinator abundance depends on landscape context as well as local factors such as field size (Kremen et al 2004; Greenleaf and Kremen 2006; Isaacs and Kirk 2010), some orchards may be able to receive full pollination by wild bees while others will need to supplement with managed bees.  In addition to the quantities of native bees present in an orchard, pollination services also depend on the pollination efficiencies of individual bee species.  That is, having many bees present in an orchard will only go so far if they are generally inefficient pollinators.  Previous studies of wild pollinators in both northern Wisconsin and New York found a diversity of bees visiting apple blossoms, though these studies did not examine the pollination efficiency of these bees or whether they could provide full pollination (Watson 2009, Gardner and Ascher 2006).  Thus the potential exists for native bees to be significant contributors to apple pollination, but it is not known to what extent they contribute or whether farmers can achieve some level of pollination “insurance” given decreased levels of honey bees.

    Previous SARE funded research has focused largely on managing lands to enhance wild bees (LNE07-261, SW08-056, GNC07-086, ONE09-107, ONE09-094, ONE05-045, GS08-077, GW09-018, LNC08-297, FNE02-411) or examined the effects of landscape context on bees (GS10-092).  Few studies have examined which bees are efficient pollinators and none have tried to determine whether wild bees alone can provide adequate pollination services to any crop.  This proposed research examines the efficiency and contribution to pollination for bees in apples and provides growers with tools to aid in bee identification.  By giving growers a way to evaluate pollinators on their lands, they can adjust or enhance conservation practices to increase native bee diversity and abundance and potentially increase crop pollination.

    Project objectives:

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

    The overall aim of this research is to help growers determine the contributions of wild bees to pollination of apples, thereby decreasing their dependence on honey bees.  The primary audience for this research is apple growers in Wisconsin and throughout the North Central Midwest where bee communities are similar.  Additional audiences include growers of other pollinator-dependent fruit, and organizations and researchers that study wild bees. Ultimately, the research developed in this proposal can help growers understand to what extent native bees provide free pollination services and help them evaluate and monitor their own pollinator community the same way that they may scout and monitor pest activity. 

    The short-term outcomes will include increased grower knowledge of which wild bees are the most efficient pollinators of apples and how these wild bees compare to honey bees.  Our research will also determine if orchards without managed honey bees can obtain pollination levels comparable to orchards with honey bees.  Growers will furthermore have an increased understanding of the numbers and diversity of wild bees needed for adequate pollination and will have resources to identify wild bees in their orchards.  

    An intermediate outcome will be that growers can assess the wild bee community in their orchards and monitor over time. With information on the relative efficacy of different bees, growers can make management decisions to conserve these efficient pollinators by providing specific floral and nesting resources.  In the long-term, growers can make more informed decisions on whether they need to rent or manage bees to augment their wild bee community.  Researchers can use the information generated from this study to work towards developing a threshold for wild bees above which growers can expect to receive adequate pollination. Growers with a wild bee community large and diverse enough to supply pollination will save money by not renting honey bees.  Additionally, an increased reliance on wild bees could result in increased participation in bee conservation efforts.  Many growers may not currently manage for native bees because they are unaware of their significance or rely largely on honey bees.   Finally, a reduced dependency on honey bees may make apples a more sustainable and profitable crop.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.