Enhancing Native Bee Populations for Pollination

PROJECT BACKGROUND
Rush River Produce is a major grower of direct marketed small fruits in Western Wisconsin. Our plantings currently include 8 acres of blueberries, ½ acre of raspberries, an acre of lingonberries, and an acre of black and red currants, gooseberries, and black raspberries. The farm is 160 acres of scenic bluff land overlooking the Rush River and Mississippi River Valleys. About 80 acres is forested and 80 acres tillable, though most of the tillable land is sloped and highly erodible silt loam soil.

We bought the farm in 1986 and have been planting an acre or more of perennial small fruit crops each year since that time. We began selling berries u pick in 1990 and have over the past 7 years grown to be a major primary tourism destination in the Mississippi Ricer corridor. Our marketing area extends over 80 miles to Minneapolis/St. Paul and Rochester, MN and Eau Clair, WI. We attracted over 2,000 customers in 1999 and expect 300 to 400 additional customers in the year 2000. We expect to have an increased supply of berries every year for the next 10 years and expect to increase our customer base by 300 to 500 families per year.

We feel that the production of perennial crops, in our case berries, when approached with the proper attitude, has the potential of being one of the most suitable forms of agriculture. The perennial nature of the crops reduces the need for tillage dramatically and reduces the associated risks of erosion and loss of soil fertility. The higher value of the crops allows us to engage in higher cost cultural practices, such as mulching, while still retaining significant income from the farm.

A SARE grant received in 1997 allowed us to test the use of organic mulch materials as a non chemical alternative for suppressing weeds in the blueberry plantings. The results of this project were impressive. Control of annual weeds was improved dramatically and adequate weed control was accomplished through spot spraying of herbicides rather than over the row applications. Additionally, the response of the berry plants to the improved growing conditions provided by the mulch was so impressive that we purchased a Mill Creek Row Mulcher and 10 truck loads of wood shavings and sawdust and have completed the mulching of all 7 acres of blueberry plants on the farm. We expect to be able to have better weed control in the future using less persistent contact herbicides on a spot spray basis.

PROJECT DESCRIPTION AND RESULTS
The project was designed to increase the on farm populations of native solitary bee species by producing and deploying nesting habitat, limiting predation of the bee nests, and by placing the bee nests in a protected are for over wintering. We normally rent 10 hives of honey bees each spring to pollinate our berry crop. The past several years we have had adverse weather during pollination season. The solitary bees are more effective at pollinating the fruit, particularly blueberries, and are active in colder, wetter and windier weather than are honey bees. Also the price of honey bee rental has gone up significantly in the past several years.

Solitary bee nesting blocks were constructed from Red Oak, Basswood, Elm and cardboard tubes. The nest structures basically consist of a series of holes, 5/16 inch in diameter and 4 to 6 inches long, drilled into wooden blocks. The cardboard tubes are the same size and are place in a waxed cardboard or wooden box. The nest boxes are placed in a sunny wall about four feet off the ground and protected from the rain by a roof shingle cover. These nesting structures may be produced from found materials such as old 4x6 inch lumber scraps, chunks of firewood, of pieces of branch. The cardboard tubes are placed in a rain proof box – an old milk carton will do fine, or you can build a wood box.

The project was started in the spring 1997 when we produced and deployed, on racks or sunny walls, set 4 feet above ground, bee nest blocks containing 150 nesting holes at three places around the existing blueberry fields. By the end of the summer of 1997, 32 of the nesting holes were filled by solitary bees, probably of the native Osmia (Orchard Mason Bee) species, while an additional 30 holes were filled by unidentified Leafcutter bee species. Six nesting holes were filled by unidentified solitary bee species.

During the winter 1997-1998 a set of nest blocks containing 500 nesting holes were produced. These were deployed, along with the ’97 blocks, in April of 1998. at the end of summer of 1998, 55 holes were filled by Osmia species, 42 holes were filled by Leafcutter species, and 17 holes were filled by unidentified species, including 6 by a wasp which fills its nest holes with dried grasses and is active in mid to late summer.

During the winter of 1998-1999 an additional set of nesting blocks containing 500 nesting holes were produced. These were deployed at the same three sites in April, 1999. At the same time non native Orchard Mason Bees were purchased and introduced. A set of 8 filled nest tubes were purchased form a supplier and deployed at one of the nest sites. Several hundred cardboard nesting tubes were purchased from the same supplier to evaluate preferences for nesting sites. The cardboard nesting tubes were assembled into nest blocks and deployed at the same sites as the imported Orchard Mason Bees. By the end of the summer of 1999 the imported Orchard Mason Bees had filled 45 nesting holes, native Osmia species had filled 75 nest tubes, leaf cutter species had filled 53 nest holes and the unidentified wasp species had filled 63 nest holes.

Nesting success rates at the three different sites varied a lot. Site A was located near the farm house an attached to the wall of an existing structure at a height of five feet. Site B was located next to a wind break to the north of the blueberry field. Site C was located in tall grass to the east of the blueberry field. It had been noticed that a small ant species, referred to as sugar ants, was entering the nest holes during and after the period bees were laying eggs. We surmise that they were stealing the pollen and nectar stored by the bees for feeding their young. They may also have been robbing eggs. In any case we presumed that the ant’s intentions were detrimental to the bees. Tanglefoot, a commercial insect trap product, was applied to the supports of all the nest sites to reduce ant activity. However, at site C the tall grasses at the base of the nest site grew past the sticky barrier and ant predation was significant. The nesting success rate at the site was greatly reduced compared to the other two sites, probably due to the removal of nectar and pollen deposited by the bees and removed by the ants. Sites A and B where the Tanglefoot was more successful, had much higher nesting success rates.

Site A was additionally protected by wire netting over part of the wood block nest site and completely covering the cardboard tube nest site at that location. The wire mesh was ¼ inch galvanized net. This net proved to be a slight impediment to the Orchard Mason Bees but it eliminated nesting by the unidentified wasp species as well as eliminating predation by woodpeckers and other birds.

All nest sites were collected in November of each year and placed in an existing barn at the farm. This was done to reduce loss of bee nest to predation by birds and mice over winter and to reduce stress on the bee larvae from extreme variations in winter temperatures. The storage area is in the bottom of the barn which is protected on three sides by an earth berm. Winter temperatures in the storage area during the period of this project rarely got below zero and were generally in the zero to ten degree range for the December through February period, despite outside temperatures ranging in themed teens below zero outside. Storage of the bee nest blocks in this temperature moderated environment has resulted in very good larvae survival rates. In the two years the nest blocks have been deployed after storage in the barn only three nest tubes didn’t “hatch”. We assume that there was some other mortality in individual larvae but we were unable to collect data to evaluate this.

The imported Osima species showed a distinct preference for the cardboard tube nesting sites. The cardboard tube nest was installed at site A a week after the Orchard Mason Bees hatched and after they had started filling holes on Red Oak and Basswood structures. After 2 weeks all the Imported Orchard Mason bees active at site A were nesting in the cardboard, leaving the wooden block to the other native species.

When selecting wood for nest block construction it is best to use dry wood. Our Red Oak nest blocks cracked and split as they dried, but after they were drilled, causing most of the drilled holes to be unattractive to nesting bees. They don’t like to use a hole with two openings.

Wood shelves were built to store the nest blocks in the barn for the first year of the project but there was some mouse activity around the nest blocks. A large metal cabinet was acquired at an auction that was constructed to be mouse proof, yet allow some air circulation. The bee nest blocks have been stored in this cabinet the past two winters with no observable loss of bee larvae due to mice.

Native Osmia bees, Imported Osmia bees, Leafcutter bees, Unidentified bee species, unidentified wasp

1997
Site A: 15, 0, 12, 3, 0
Site B: 11, 0, 8, 1, 2
Site C: 6, 0, 10, 2, 0
Total: 32, 0, 30, 6, 2

1998
Site A: 18, 0, 18, 5, 1
Site B: 15, 0, 10, 5, 6
Site C: 12, 0, 12, 3, 2
Total: 45, 0, 40, 13, 9

1999
Site A: 21, 29, 14, 4, 1
Site B: 18, 8, 18, 5, 70
Site C: 8, 2, 12, 3, 16
Total: 47, 39, 44, 12, 87

We find the results of this project to be very encouraging. Native solitary bee species populations are increasing at a rate of over 50% for two years. The imported Orchard Mason bees are reproducing at a more rapid rate – almost 500% in the first year after introduction. If the imported Orchard Mason bees over winter well they will be a great addition to the selection of pollinators available for spring pollination of berry crops. The unidentified native wasp seems to be increasing at an even more rapid rate, over 40 times in two years – while we have no information as to the identity or usefulness of this wasp we plan to allow it to share in the use of some of the nest sites as an unplanned bonus.

The results of this project were excellent from our perspective. The population of solitary bees, both native and introduced, is increasing at a rapid rate. Observations in the blueberry fields during the blossom period show that solitary bees are more numerous, or at least more noticeable, and certainly more active during cool weather. The project has shown that solitary bee nesting habitat can be manufactured and deployed for a minimal cash outlay, and with only a modest investment in labor. If the solitary bee population keeps increasing at the current rates it will take several more years to grow the population to the point that we won’t need honey bees to pollinate the blueberries. However, the existing increase in population should serve to promote more complete blueberry pollination during springs with adverse weather condition during bloom.

OUTREACH
Outreach during this project was ongoing. As a u pick berry farm we have a continuous flow of customers at the farm during the July-September period. Project tours were given to 45 interested berry customers during the berry picking season. A field day was held on May 23, 1998 and was attended by 12 interested parties. More formal tours were given to the Pierce County Supervisors and a Horticulture class from the University of Wisconsin – River Falls in 1998 and 1999. Additional requests for information were received by phone and email from 18 people. A significant amount of time was spent responding to inquiries. A press release concerning the project was sent out in the spring of 1999 resulting in a live on the air interview on WCCO Radio (Mpls, MN) and a mention in the local print media. An additional field day will be held in July of 2000. This report will be posted on www.rushriverproduce.com, an informational web site currently under construction.