Project Number: 2080-21000-019-20-R
Project Type: Reimbursable Cooperative Agreement
Start Date: Jan 1, 2019
End Date: Sep 29, 2021
Efficient pollination of tree fruit crops is a necessary component of orchard management. For decades, fruit producers have relied entirely on managed honey bee colonies to meet these pollination requirements, due to their ease of transport, well-studied biology and history of use. However, it has long been recognized that honey bee pollination of tree fruit orchards come with some inherent limitations, such that honey bees do not always fully meet the needs of agricultural producers. These limitations are perhaps most notable in two specific specialty crops grown in Washington State: Pears and sweet cherries. Many commercially grown varieties are self-incompatible and require cross-pollination with co-blooming ‘pollinizer’ pear varieties to set fruit. Honey bees are widely acknowledged to be poor pollinators of pears. Pear blossoms offer foraging bees nectar that is low in sugar relative to most other flowering plants; this is the main reason why honey bees are averse to foraging in this crop. This aversion is evident throughout published literature, which frequently recommends the elimination of any competing bloom within the foraging range of managed honey bee colonies and twice the bee hives per acre in pears than in other fruits. Just as with pears, many sweet cherry varieties require effective cross-pollination to set fruit, and this cross pollination is not always achieved with the use of managed honey bee colonies. In addition, cherries bloom early in the spring, when cooler and wetter weather conditions may not favor honey bee foraging. To circumvent some of the limitations of honey bee pollination in Washington pears and sweet cherries, we propose the use of an alternative, commercially available bee called the blue orchard bee (BOB) as an effective co-pollinator of orchard crops. This native, solitary bee is a proven pollinator of spring-blooming rosaceous crops including tart cherry, apple and almond. Unlike honey bees, BOBs have only one generation per year, and are free-flying adults for just four to six weeks annually. This active period can be manipulated to occur at any time between February and May using standardized management and incubation practices; thus, they can be made available whenever bloom is expected to occur. The BOB is a Spring-flying bee that forages in cooler temperatures than honey bees do, which makes them particularly well-suited for early-blooming and/or high elevation orchards. They also collect and store pollen dry, underneath their abdomen (nestled between coarse hairs known as ‘scopa’) which leads to increased rates of pollen deposition and cross-pollination when compared to the honey bee, who stores her pollen in tightly-packed pollen baskets. Finally, blue orchard bees typically forage within 60m from their nest and thus provide more localized pollination services than honey bees typically would. The proposed study would be the first to report on the potential success and influence of BOB pollination on commercial pear and sweet cherry fruit production.
We have identified several orchard managers in Washington State who maintain orchards with historically poor fruit production attributed to ineffective pollination. This project would entail using blue orchard bees in combination with existing honey bee colonies to evaluate whether typically low fruit yields can be enhanced as a result of BOB pollination consistently over a three year period. BOBs will be introduced to three separate, five-acre plots of 1) pears and 2) sweet cherries during their respective bloom periods from 2019 to 2021. Special care will be taken to ensure that all three replicates for both crops are controlled (as much as possible) by age and variety, and subjected to similar orchard management practices. Bees will be released and managed according to established, standardized practices. After bloom ends, fruit will be permitted to set and develop naturally over the course of the season. At harvest, we will return to the experimental plots and work with orchardists to determine average fruit yield per acre in the experimental plots. Fruit yield per acre will be compared to historical yield averages for the same orchard to examine the relative impact of BOB pollination on orchard performance for each year of the study. Additionally, these yield averages will be compared to fruit production of neighboring orchards that did not receive the added benefit of BOB pollination services. If experimental orchards reveal consistent increases in fruit yield over time and relative to other neighboring orchards within year, it will confirm that BOB pollination provides an overall net benefit in orchard blocks where they are introduced. BOB reproduction will also be evaluated over the three years of this study. Sustainable propagation of blue orchard bees in managed orchards would drastically reduce the annual expense of purchasing BOBs for pollination year after year. In Utah tart cherry orchards, we have observed two-fold reproduction of blue orchard bees in 2016, which leaves us hopeful that high rates of bee propagation in Washington pears and sweet cherries are possible. To evaluate annual blue orchard bee reproduction in the orchards, we will collect and store completed BOB nests within the USDA-ARS Pollinating Insects Research Unit lab each year, where X-radiography can be used nonlethally to sex and diagnose any parasitism or diseases in the resultant BOB progeny. To confirm BOB foraging preference for pears and cherries over any competing bloom, we will collect samples of pollen from completed BOB provisions in experimental orchards. From each 5- acre experimental orchard block, approximately 10 completed BOB nests will be collected at random. From each nest, a small sample of pollen, stained with fuchsin jelly, will be collected from the terminal (most recently completed) provision. These pollen samples will be evaluated under a microscope to estimate the average proportion and volume of the provision that is made of pear/cherry pollen. From this, we hope to quantify BOB foraging fidelity within their target orchards.