Improving Pollination for the Northeast: On-Farm Testing, Demonstration and Management of the Alfalfa Leafcutting Bee

Improving Pollination for the Northeast: On-Farm Testing, Demonstration and Management of the Alfalfa Leafcutting Bee

Summary

Key Findings
This research provides an alternative to the honey bee for blueberry and cranberry pollination, which make pollination of these economically important crops more sustainable. Our study suggests that:
The alfalfa leafcutting bee (ALB) is a good alternative pollinator of highbush blueberry in fields that are relatively weed-free.
Economic analyses indicate that the ALB can provide a net economic benefit to growers for blueberry, but not for cranberry at the present

Objectives
1.Test the alfalfa leafcutting bee (ALB) as a pollinator of highbush blueberry and cranberry.
2.Develop pollination management practices for the ALB designed for highbush blueberry and cranberry.
3.Demonstrate handling, care, and management practices for the ALB to farmers.
4.Evaluate the economics and cost effectiveness of using the ALB as a pollinator of blueberry and cranberry.

Method and Findings
Results from two field seasons (1995-1996) involving 15 participating farmers, combined with our greenhouse bioasssay results (1995-1997) indicate that the alfalfa leafcutting bee (ALB) is a good alternative pollinator of highbush blueberry in fields that are relatively weed-free. Statistical analyses indicated that the ALB and honey bee performed similarly for both highbush and cranberry on the following parameters that measure pollinator effectiveness: fruit set, yield, berry weights, and seeds per berry. Observations of foraging behavior in the field and pollen analyses indicated that the ALB was more faithful to cranberry, whereas the honey bee was more faithful to highbush blueberry. Greenhouse flight cage studies showed that flower handling time and pollen deposition were better for the ALB than the honey bee.

Reproductive output was not high on either crop, nor on alfalfa, which suggests that at least some bees would have to be purchased on an annual basis, much like the annual renting of honey bees. In 1997, the ALB was successfully field released on lowbush blueberry by one of the participating growers demonstrating some farmer adoption of this new alternative pollinator to the honey bee for small fruits.

Specific Findings
Our fruit set findings demonstrated that the ALB is as effective as honey bees for this parameter and that the use of commercial pollinators improves fruit set. For highbush blueberry and cranberry, fruit set was high for both the ALB and honey bees.

Several aspects of yield were investigated: 1) percentage yield (number of ripe fruits) number of flowers on marked branches or uprights), 2) average berry weight, and 3) average melanized seeds per berry. Our blueberry and cranberry findings demonstrated that the ALB is as effective as honey bees for this parameter and that the use of commercial pollinators improves yield. Highbush blueberry weights for the two year period were not significantly different which suggests that the ALB pollinates as well as honey bees and native pollinators.

The foraging behavior of the ALB in terms of fidelity to the blooming crop versus fidelity to other plants in bloom at the same time was examined. The ALB was more faithful to cranberry compared to highbush blueberry, whereas just the opposite occurred for honey bees. Native pollinators (bumble bees, andrenids and leafcutting bees) were more faithful to the blooming crop than either ALB or honey bees. Management of weeds during bloom is essential to keeping the ALB faithful to the crop, just as it is for the honey bee.
Overall, the greenhouse flight cage studies demonstrated that the ALB is a more efficient pollinator of cranberry than the honey bee based on flower handling time and pollen deposition. No significant differences in pollen deposition existed for blueberry.

This project addressed four major management questions: 1) stocking density, 2) nesting success (production of viable offspring) on the blooming crop, 3) nesting success on a second crop (migratory strategy), and 4) nesting success on alfalfa.

Nesting success is determined by comparing the number of bees produced to the number of bees released (the reproductive ratio). In all cases the number of cells (bees) produced was less than the number of cells (bees) set out. The migratory strategy of moving the bees to new forage at the end of bloom did not significantly affect the number of bees produced. It appears that farmers will have to buy some bees from suppliers on a yearly basis much like they rent honey bee hives.

Based on the results in highbush blueberries, it seems reasonable to assume that both species provide a net benefit to growers. If honey bee supplies continue to shrink and rental prices per hive continue to rise, then ALB bees may become a profitable alternative on cranberry in the future. The costs of hive rental for honey bees in Maine in 1996 and 1997 were $40-$55/acre, up more than 30 percent in three years.
Reported November 1997.

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