A Measurement of the Pollination Success of Native Bees in North Georgia Apple Orchards: Is there a need for Commercial European Honeybees?
Honeybees (Apis mellifera L.) are a vital part of human agriculture. It is estimated that bees pollinate approximately one-third of all human food crops. To get high crop yields, most farmers rent honeybee hives from beekeepers to boost the number of bees pollinating their crops. It is estimated that the value of honeybee pollination to U.S. agriculture is over $15 billion each year.
Worldwide agricultural operations, however, are facing a growing dilemma that has the potential to jeopardize traditional farming practices and ultimately affect food production: the unprecedented decline of the European Honeybee (Apis mellifera). Especially prominent in the Western Hemisphere since the mid-1990s, Colony Collapse Disorder (CCD) threatens to decrease production of such staple fruit crops as peaches, almonds, cherries, and, of specific focus to this study, apples.
However, honeybees are not responsible for 100% of the pollination of agricultural crops. An untapped solution common to every agricultural site is the incredibly diverse assortment of native bees. Many of the species within this broad community have great potential to supplement or replace the dwindling honeybee as the primary pollinator for many diverse crops, with little more than simple habitat alterations.
The main goals of the current project were: (1) to identify the native bees present in or near North Georgia apple orchards, and (2) to measure the pollination success of the native bees.
During the course of the study, in the 2011growing season, nearly 3000 native bees were collected from four North Georgia Apple Orchards. The bees were collected from March until October 2011. Unusual weather events and a two-week early apple bloom resulted in changes in species composition of the native bees during the 2011 apple bloom.
Experiments using netting enclosures showed that native bees have the ability to fully pollinate apple trees. There were no significant differences between control branches that were pollinated by honeybees and native bees and branches that were pollinated only by native bees.
The study had two main goals. The first goal was to conduct a survey of the native bees present in North Georgia Apple Orchards from March to May, in order to measure native bee species diversity and abundance before, during, and after the apple bloom. The second goal was to measure the success of native bees in apple pollination and fruit production.
GOAL 1 – Survey of Native Bees in Georgia Apple Orchards
Native bees were collected using several types of insect collecting traps. These traps included: pan traps, vane traps, and malaise traps. Insect diversity and abundance was measured 2 weeks before the bloom, weekly during the bloom, and once a month after the bloom. During collection days, the traps were set up in the morning and remained up until dusk, which yielded a 12-hour collection period.
The four orchards surveyed were:
Mountain View Orchards (2984 Mobile Road, McCaysville, GA 30555)
Mercier Orchards (8660 Blue Ridge Drive, Blue Ridge, GA 30513)
Hillside Orchards (105 Mitcham Circle, Tiger, GA 30576)
Tiger Mountain Orchards (1309 Bethel Road, Tiger, GA 30576)
GOAL 2 – Measuring the Success of Native Bees in Apple Pollination
In the following experiment, ten apple trees were randomly selected. In each selected tree, branches of the tree were enclosed with small mesh netting that excluded commercial honeybees from entering the enclosure and pollinating the flowers of the selected apple tree. Based on our preliminary research (2010 field season in the apple orchards), we determined that over 80% of native bee species are smaller than the commercial European honeybees. Small size native bees were able to enter the netting and perform pollination activities. In each enclosure, a large pan trap was placed inside to collect a sample of all the native bees that entered the enclosure prior to, during, and after the apple bloom. The enclosures were placed over the trees several weeks prior to the apple bloom and removed after 95% or more of the apple flowers fell off the apple tree.
Four different measurements of pollination success were taken during the apple season. These measurements included: (1) percent of flowers pollinated, (2) the effectiveness of pollination on each flower, (3) number of apples produced per branch, and (4) average size of apples produced. For each selected tree, we compared the enclosed branches (experimental group) with similar sized unenclosed branches (control group). At each orchard, we set up ten experimental trees.
The project had two main goals: (1) to identify the native bees present in or near North Georgia apple orchards, and (2) to measure the pollination success of the native bees.
Goal 1- To identify the native bees present in or near North Georgia apple orchards throughout the year.
During the 2011 growing season (March- October 2011), 2928 native bees and 390 native wasps were collected. The most abundant bee taxa identified were: Andrena (Mining bees), Lasioglossum (Sweat bees), Xylocopa ( Large Carpenter Bees), Ceratina (Small Carpenter bees), Bombus (Bumble Bees), genera in the Tribe Augochlorini (Green Sweat bees). Native bees collected in the 2011 season are listed Table 1.
The different groups of native wasps are presented below in Table 2. The native wasps are shown because they were observed landing on the apple flowers, and some wasps are known to drink the flower nectar. Over 60% of the wasps collected were Tiphiid wasps (flower wasps).
GOAL 2 – Measuring the Success of Native Bees in Apple Pollination
This year, we had mixed results on a preliminary measurement of the success of native bees in apple pollination. Due to unusually severe weather, including tornados and strong winds in the orchard area of North Georgia, most of our netting enclosures, as well as numerous apple trees in the orchards, were damaged and/or destroyed. Only one enclosure in the Mountain View Orchard remained perfectly intact. In this enclosure, native bees were successful in pollinating the apple blooms. These branches produced a total of 18 apples, which was similar to un-netted branches on the same tree. There were 16 bees captured in the pan traps in the enclosure: 4 Andrena (Melandrena) carlini, 5 Andrena forbseii, 1 Andrena illicis, 5 damaged Andrena (Trachandrena) species, and 1 Lasioglossum (Dialictus) imitatum. Based on this limited study, bees in the Andrenidae family (mining bees) are likely to be the most important native pollinator in North Georgia Apple Orchards.
Tentatively, it can be stated that native bees are capable of fully pollinating the apple trees. Honeybees are not needed for commercial apple agriculture if an adequate number of native bees are present.
Impacts and Contributions/Outcomes
The 2011 study found that most Georgia apple orchards have diversity and abundant sources of native bees. Almost 3000 native bees were collected in the 2011 growing season. Over 100 native bee species have been identified in Georgia Apple orchards.
This study has identified the target native bee(s) for apple pollination in North Georgia as Andrena crataegi and Andrena (Melandrena).
The limited netting experiment showed that native bees are capable of pollinating apple flowers and producing large size apples, in the same frequency as apple trees pollinated by a combination of honeybees and native bees. It can be concluded that native bees have the potential to replace honeybees in apple pollination.
In the 2012 growing season, we will confirm this finding with an additional netting experiment.
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