Nesting Habitat Enhancements and Native Bee Population Measurements in Apple Orchards in Georgia

View the project final report

Commodities

• Fruits: apples

Practices

• Crop Production: beekeeping

Honeybees contribute $15 billion in pollination services to U.S. commercial agriculture annually. The yields of some crops decrease by more than 90% when honeybees are not present. Reliance on a single insect species, the honeybee, for the pollination of over 1/3 of the human food supply can be dangerous. Alternative pollination strategies that are less dependent on the honeybee must be developed in order to ensure long-term sustainably of insect pollinated crops.   The best alternative to honeybees is the native bees already present in the local environment. With nearly 3500 species in North America alone, the diversity of different forms, pollen-strategies, and behaviors of native bees provide a wide range of use for agricultural operations. Therefore, research is needed to determine which native bees are present in a given region and how best to enrich the habitat (e.g. nesting areas) to increase target native bee populations.   Our studies have identified the mining bee, Andrena Crataegi, and its close relatives, the Melandrena, as being the ideal native bee species for Georgia Apple production. Other excellent apple pollinating native bees indentified were the carpenter bees (Xylocopa virginica) and mason bees (Osmia species). It is time to expand the study to the next step: (1) to estimate the native population sizes in the orchards, and (2) to develop habitat enrichments and other strategies to increase the abundance of these target native bees in the apple orchards.   By establishing a strong network of native bees in Georgia agriculture, we can make Georgia agriculture more secure and sustainable. In addition, an increase in reliance on native bees means that farmers will spend less money on pollination services (e.g. renting honey bee hives), which will result in greater farmer profits and potentially reduce food costs for the general public.

For the 2014 field season, we have 3 main objectives. The first objective is to gain a better understanding of native bee population sizes and their distribution in the orchard. The second objective is to develop habitat enrichments to boost the abundance of specific native bee species. The third objective is to survey native bee abundance and diversity in the apple orchard. Native bee diversity and abundance shift during the apple bloom and can vary depending if very early or late apple bloom periods occur.

Objective 1 – Measuring Native Bee Population Numbers and Determining Their Distribution in the Orchard

We will use the technique of mark and recapture method to estimate population numbers of target native bees in the apple orchard. Using a modified version of this technique (using bee paint of different colors to denote different areas in apple orchard), we will be able to determine bee ranges and distributions in the orchard.

N =MC/R

N = Estimate of total population size

M = Total number of animals captured and marked on the first visit

C = Total number of animals captured on the second visit

R = Number of animals captured on the first visit that were then recaptured on the second visit

Objective 2 – Boosting Target Native Bee Abundances with Nesting Habitat Enrichments

In order to boost the abundance of the target native bee species, the mining bees (Andrena Crataegi and other Melandrena species), nesting habitat enrichments sites will be created on one side of the orchards. Trenches excavated will be 4 feet long x 2 feet wide x 12 inches deep. Mining bees prefer patches of soil in which to dig tunnels for their habitat and a place to brood their young. In addition, early blooming plants (e.g. cherry trees) will be placed just behind the trenches to recruit native bees to the orchard before the apple trees even flower. Based on our previous studies, floral enrichments and bare-soil trenches should attract the mining bees. In order to assess the success of the enrichments for boosting the abundance of the mining bees, we will examine the trenches for holes (entrances to new colonies). We will also compare native bee abundances on the nesting habitat enrichment side of the orchard with the other side that did not receive enrichments.

In order to boost the abundance of the secondary target bee species (mason bees), four special nesting boxes will be created within each plot.  The center of the nesting box will contain a large section of about sixty 9-mm diameter tubes (prime nesting sites for mason bees). In order to assess the success of the collection tubes in the nest box for boosting the abundance of the mason bees (Osmia species), we will examine each individual tube to get an exact count of the Osmia. This examination will not harm the developing bee.

Objective 3 – Survey of Native Bees in Georgia Apple Orchards

The third main objective is to continue the survey of the native bee pollinators for a fifth year within the apple orchards, with a focus placed specifically on the apple bloom periods.   Significant weather changes, perhaps due to global warming, have resulted in drastically different growing seasons in the past four years. In 2010, the apple bloom exhibited a traditional pattern of blooming in early to mid-April. The apple bloom shifted 4-5 weeks earlier in 2011 and 2012 from the typical bloom. These much earlier apple blooms were pollinated by a different composition of native bees. For example, mason bees, (Osmia species) were more abundant during early apple blooms. In 2013, the apple bloom occurred two weeks late (late April), resulting in fewer mason bees and more mining bees.

In these orchards, native bees will be collected using several types of insect collecting traps and procedures, including pan-traps, vane-traps, malaise-traps, and timed sweep-netting.   Insect diversity and abundance will be measured 2 weeks prior to and after the bloom, and weekly during the bloom itself. The traps will be set up around dawn and will remain up until after dusk during collection days, which is a typical 12-hour collection period.

At each orchard, there will be a total of 13 sets of pan-traps. Each set includes 1 white, yellow, and blue pan painted with UV-reactive paint. In each orchard, 6 sets of vane traps will be used. Each set includes 1 blue vane trap and 1 yellow vane trap. Likewise, 3 malaise traps will be set-up (1 trap in the center of the orchard with the other 2 traps near the edge of the plot) for each sample day.

After the collection, all the bees will be brought back to the GGC laboratory to be counted and identified. Bees will be determined to species and either preserved in ethanol or pinned and mounted in permanent collection boxes.