Enhancement of Native Bee Pollination Services in Apples Orchards in Georgia
Bees pollinate approximately 1/3 of the food we eat. They pollinate all of our fruits, nuts, and vegetables. Honeybees contribute approximately $15 billion in pollination services to U.S. commercial agriculture annually. However, reliance on a single insect species, the honeybee, for the pollination of a huge portion of the human food supply can be dangerous. Indeed, this is especially true considering that honeybees are in decline from Colony Collapse Disorder (CCD), thus putting the global food supply at risk. Today, honeybee colonies are down by 40% compared to the 1970’s.
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 provides a wide range of use for agricultural operations. It is estimated that native bees already annually contribute $3 billion to U.S. agriculture.
Over the past four years, the current study has examined the different native bee species in Georgia apple orchards. The mining bees (Family Andrenidae: Genus Andrena) show the greatest promise as a native bee that could replace or supplement the honeybee in early blooming crops (April- May) such as apples, blueberries, etc. Mason bees (Family Megachilidae; Genus Osmia) may also be important in Georgia agriculture when the apple bloom is particularly early (march or April) as seen in 2012 and 2013.
In the 2013 growing season (March-September), 5047 bees from 28 Genera were collected during the survey. The mining bees (58.2% of the sample) clearly dominated the samples taken in the apple orchard. There is little doubt that mining bees are the key native bees for early blooming commercial crops in Georgia. Native bee diversity and abundance were similar to previous years, perhaps even a little higher. Mason bee abundance (54 bees collected) was lower than the previous year, but still higher than in 2010 or 2011.
Habitat enrichments were created to boost the abundance of both of these target groups (mining bees and mason bees). Both types of habitat enrichments showed promising results.
The main objective of the study is to create habitat/nesting enrichments that will maximize the overall abundance of the previously identified target bee species (mining bees and mason bees). These nesting/habitat enrichment areas are hypothesized to increase the abundance of the targeted native bees already present in the orchard.
In order to boost the abundance of the main native bee target species, the mining bees (Andrena crataegi and other mining bee species), soil enrichments sites will be needed. These bees prefer patches of soil in which to dig tunnels for their habitat and a place to brood their young. At each orchard, four trenches (about 12 inches deep and 60inches long X 18 inches wide) will be excavated.
In order to boost the abundance of the secondary target bee species (mason bees) four special nesting boxes for the bees will be created within each plot. The center of the nesting box will contain a large section of about sixty tubes (varying from 6mm to 8 mm) or wooden boxes with 40-80 holes (8 mm diameter).
The secondary objective is to continue the survey of the native bee pollinators for a fourth 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. The apple bloom has shifted 4-5 weeks earlier in the past two years from the typical bloom in April. These much earlier apple blooms can impact which native bees are present to pollinate them (e.g. mason bees, Osmia species, are more important during early apple blooms).
Mining bee (Andrena species) enrichments
Four trenches were created at each orchard, in order to boost the abundance of the mining bees (Andrena crataegi) and other mining bee species. Mining bees prefer patches of soil in which to dig tunnels for their habitat and a place to brood their young. Two trenches were placed at opposite sides of the sampling plot in each orchard. On one side floral enrichments (e.g. 2 cherry trees and 2 bushes that bloom before apple trees) were added around the trenches, while on the other side “control group side” no trees or bushes were added around the trenches. At each orchard significant nesting took place in the trenches. Both mining bees and sweat bees were observed to nest in the trenches. In addition, nesting frequency was more than double on average in “floral enrichment” trenches compared to the control group trenches without floral resources. Bee nesting increased in the trenches throughout the apple bloom. Nesting in the trenches ended mid-May.
Mason bees (Osmia species) Enrichments
Eight nest boxes were created at each orchard in order to boost the abundance of the secondary target bee species (mason bees). Four nesting boxes were placed at opposite sides of the sampling plot in each orchard. Three of the nest boxes contained a wooden block with 8mm holes drilled into the length of the box and one nest box contained 60 nesting tubes (6 mm, 7mm, and 8mm tubes). On one side, floral enrichments (e.g. 2 cherry trees and 2 bushes that bloom before apple trees) were added around the nest boxes, while on the other side “control group side” no trees or bushes were added around the nest boxes. At each orchard significant nesting took place in the nest boxes.
Five mason bee species nested in the nesting boxes. The two most common species nesting in the nest boxes were Osmia georgica and O. taurus. Significant parasitism took place in all orchards. Parasitism was much greater in wooden nesting boxes compared to the nesting tubes. 136 Osmia cocoons successfully developed. The highest level of nesting took place in 6 mm tubes, predominately Osmia georgica. The second highest level of nesting took place in 8 mm tubes or wooden nest boxes, predominately Osmia taurus.
During the 2013 growing season (March-September), 5047 bees from 28 Genera were collected during the survey. The 3 most common groups were Genus Andrena (mining bees) (58.2% of the sample), Genus Lasioglossum (sweat bees) (16.3% of the sample), and Genus Apis (honey bees) (9.9% of the sample). Andrena crataegi continued to be the most common bee species collected in the apple orchard. See Table 1 for more information.
Four orchards were sampled approximately 9 times (4 times during the bloom) from March to September 2013. Mountain View Orchard (small-scale “typical” Georgia orchard) exhibited very high levels of native bees (both diversity and abundance); while Mercier Orchard (largest orchard in Georgia) exhibited very low native bee abundance. Mercier Orchards had similar bee diversity levels (at least at the genus level) as Mountain View Orchards. However, Mercier had only 10% of the abundance that Mountain View exhibited. This may suggest that large-scale orchards require habitat enrichments in order to maintain target native bee groups in useful numbers.
Impacts and Contributions/Outcomes
This project has taken the first step in the identification of native bees that have the potential to replace or supplement honeybees in apple pollination in Georgia. Next, researchers need to develop procedures and methods to increase the abundance of these target native bees. The current project has shown that by providing habitat enrichments (e.g. nesting sites), we can boost native bee abundance. Once researchers have developed a methodology to identify and maximize the abundance of target native bees for a broad range of Georgia crops, we can state sustainable agriculture in Georgia is safeguarded.
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) that will increase farmer profits and potentially reduce food costs for the general public.
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