Native Bee Assessment in North Georgia Apple Orchards: Measuring Diversity and Devising Methods to Boost Abundance

Native Bee Assessment in North Georgia Apple Orchards: Measuring Diversity and Devising Methods to Boost Abundance

Summary

European Honeybees (Apis mellifera) play a vital role in pollinating the majority of all human agriculture, excluding cereals. Becoming so dependent upon a single species to pollinate such a large facet of food production has proven unsustainable, especially as worldwide declines intensify. Since 2006 alone, a 30% reduction in managed colonies of honeybees in North America has placed much of Georgia’s agriculture at potential risk by lowering crop yields and by increasing pollination costs (renting honeybee hives). Failure to act now could lead to future issues without the capital or time required to uncover adequate solutions.

It is prudent to find possible solutions and alternatives before a serious crisis develops. To safeguard Georgia agriculture, researchers must not only look for answers to Colony Collapse Disorder (CCD), but they must also devise alternatives to the honeybees if researchers fail to fix CCD and the other issues decimating honeybee populations.

One possible alternative to using honeybees is to use native bees for pollination services. Native bees could be used to supplement or replace the honeybee in the pollination of a specific crop. To investigate the potential native bees have for supporting commercial agriculture, a three-step approach must be taken. Step one is to perform native bee species surveys in order to know which species are present in a given farm or orchard. Step two is to identify specific native bees as potential target pollinators for certain cultivated plants. Step three is to perform minor habitat modifications to increase the abundance of the target native bees. The two most important modifications would be (1) adding native bee nesting habitat useful to the target native bee and (2) adding floral resources (e.g. wildflowers, which will provide food resources for the bees when the target crops are not flowering). Once researchers have identified these target native bees, U.S. agriculture will be afforded not only a new insect pollinator, but a sustainable and natural one as well.

The current project examines the use of native bees in commercial apple production in Georgia. Studies from previous years have identified the target native bees (Andrena species) best suited for the pollination of apples. This year, an additional survey will confirm the target native pollinators, as well as measure the pollination success of these bees. In additional, preliminary habitat enrichments will be investigated. The overall result of this research will be to reduce Georgia farmers’ reliance on commercial honeybees.

Objectives/Performance Targets

The project has three main objectives.

Objective 1 – Survey of Native Bees in Georgia Apple Orchards

A survey of native bees will be conducted in four North Georgia Apple Orchards. This will be the third year of the survey. Long-term studies have the ability to assess the effects of weather (e.g. rainfall, global warming), and bloom period (e.g. early vs. late) on native bee populations as well as measure shifts in native bee populations.

Objective 2 – Measuring the Success of Native Bees in Apple Pollination

Ten apple trees will be selected at random. Several branches of each tree will be enclosed by mesh netting of a gauge small enough to exclude the honeybee.

In each enclosure, a pan trap will be placed inside to collect a sample of native bees that enter the enclosure to pollinate the apple flowers. The enclosure will be placed over the trees several weeks prior to the apple bloom and removed several weeks after the apple flowers fall off the apple trees.

The pollination success will be evaluated by three measurements: (1) the number of apples produced per branch; and (2) average size of apples produced, and (3) seed count.

Native bees captured in the pan trap will be identified to species. This will assist in identifying the ideal target pollinators of apples.

Objective 3 – Determine the Potential Usefulness of Nest Boxes in Boosting Native Pollinator Abundance

Small orchards surrounded by areas of natural vegetation (e.g. Mountain View Orchard) have a much larger abundance of native bees than larger orchards (e.g. Mercier Orchards) (Schlueter and Stewart, unpublished data).

The Mountain View Orchard is a typical small-scale orchard surrounded largely by natural vegetation (continuous tracts of habitat impacted little by humans). Mercier Orchards, alternatively, is a large-scale orchard surrounded by limited natural vegetation fragmented by human activity through agricultural and residential operations. Due to its massive orchard size (the largest orchard in GA, with over 215,000 apple trees), we have found that this orchard has a reduced diversity and number of native bees, particularly as a person moves to the center of the orchard. Can nest boxes help boost native pollinator abundance?

We will place nest boxes in the Mountain View Orchard. In September, we will retrieve the nest boxes from the orchard. We will measure the native bee species diversity and abundance in the nest boxes. The nest boxes from the Mountain View Orchard will be placed in the center of the Mercier Orchard to overwinter for use in the next growing season.

Looking ahead; in the following growing season of 2013, we will determine if the additional nest boxes increased the number and diversity of Andrenid bees. Additional projects in 2013 will determine if increased abundance can be maintain by placing additional nest boxes (habitat sites) around the orchard.

Accomplishments/Milestones

Objective 1 – Survey of Native Bees in Georgia Apple Orchards

During the 2012 collection season (March –September 2012), we collected a total of 4712 bees. There were 828 honeybees and 3884 native bees. Native bees were represented by 1759 bees (45.3%) from the Family Andrenidae, 799 native bees (20.6%) from the Family Apidae, 43 bees (1.1%) from the Family Colletidae, 1078 bees (27.8%) from the Family Halictidae, and 205 bees (5.3%) from the Family Megachilidae. There were 94 different species of native bees collected during the 2012 field season.

During the apple bloom (March –April 2012), we collected a total of 3068 bees. There were 623 honeybees and 2445 native bees. Native bees were represented by 1519 bees (62.2%) from the Family Andrenidae, 490 native bees (20.0%) from the Family Apidae, 30 bees (1.2%) from the Family Colletidae, 298 bees (12.2%) from the Family Halictidae, and 108 bees (4.4%) from the Family Megachilidae.

Andrena Crataegi and the other Andrena bees continue to be the most abundant native bees during the apple bloom. Native bee abundance and diversity was very high in 2012.

Objective 2 – Measuring the Success of Native Bees in Apple Pollination

At Mountain View Orchards (McCaysville, GA), ten apple trees (Malus domestica Borkh.) were selected for this experiment. On each tree, two similar branches (e.g. similar bud numbers and length) were selected. Net covered cages, which kept out honeybee-size and larger bees, were placed over one of the selected branches on each of the ten trees (experimental group). The other branch (control group) was left uncovered. All ten apple trees produced blossoms on both control and experimental branches. The apples of the first set of five trees (control branches and experimental branches) were examined in mid-June. Each immature apple was measured for size (circumference) and the number of seeds in each apple was counted. The mid-June sampling occurred just before the “apple drop” period, when apple trees naturally drop some of their apples in order to devote more energy to the remaining apples. In August, mature apples of the second set of five trees (control branches and experimental branches) were examined. Each apple was measured for size (weight and circumference) and each apple’s seeds were counted. Seed count is an important measurement since it is a direct measure of pollination success. T-tests compared apple weight, apple circumference, and seed number between control and experimental branches. Statistical analyses indicated that there were no differences between the control and experimental groups in any of these measurements. The most common native pollinators captured in pan traps within the net covered cages were Andrena crataegi (72%)and Andrena carlini (15%). Andrena crataegi was identified as the “apple bee” for the Georgia Apple producing region.

Objective 3 – Determine the Potential Usefulness of Nest Boxes in Boosting Native Pollinator Abundance

For this objective, we created 10 large (20 gallon) nesting boxes. Five nesting boxes were placed above ground and 5 were placed at ground level (e.g. placed in a hole). Several of the nesting boxes showed good initial results, with bees creating burrows near the edge of the boxes. However, nest box colonization was very low when compared to bare earth patches. Also, later in the field season, ants and other non-pollinating insects seemed to dominate the boxes. Our result indicated that nest boxes are not good habitat enrichment for native bees, especially mining bees (Family Andrenidae).

In the 2013 field season, we plan to create target enrichment areas with several 5 x 2 foot trenches combined with floral enrichments (trees and plant that flower 2-4 weeks prior to the apple trees). It is believe this more natural habitat enrichment will attract and maintain more mining bees and other ground nesting native bees.

Impacts and Contributions/Outcomes

Andrena crataegi was identified as the “apple bee” for the Georgia Apple producing region.

The study’s results support the hypothesis that native bees are effective pollinators in commercial apple production and can provide a natural and sustainable agricultural alternative to the declining honeybee.

This study’s results (more than 100 native bee species identified) documents the great abundance and diverse of native bees in agricultural habitats. This incredible reservoir of pollinating species has the potential to pollinate most, if not all, of our commercial fruit and vegetable crops.

Collaborators: