High Density Honey Bee Stocking Rates Increases Yield Components of Northern Highbush Blueberry in Western Washington

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1 High Density Honey Bee Stocking Rates Increases Yield Components of Northern Highbush Blueberry in Western Washington Matthew Arrington 1 and Lisa DeVetter 2 1 PhD Candidate, matthew.arrington@wsu.edu, 2 Assistant Professor, Department of Horticulture, Washington State University Northwestern Washington Research and Extension Center, Mount Vernon, WA 98273

2 Pacific Northwest Production Washington State produces the most blueberries nationwide (USDA, 2016) In 2016 Washington produced: ~60,000 tons of berries 10,000 acres of land in production Photo credit (bottom): Imgarcade.com

3 Background Reports of poor pollination and fruit set, which limits yield, particularly in western WA DeVetter et al. (2016) found honey bee visitation rates in western Washington blueberry were below recommended guidelines; 4-6 bees per bush\minute (Isaacs et al., 2015) Photo credit: allposters.com

4 Honey bees The Italian honey bee (Apis mellifera ligustica ) is the most common commercially used subspecies Lacks co-evolution with Vaccinium sp. no buzz pollination shorter average tongue length than bumble bee pollinators (Bombus sp.) honey bee foraging may be reduced Air temperature below 65 F With wind above 12 mph With precipitation (Woyke et al., 2003) Photo credit: bottom, commandpestcontrol.com

5 Brief Note on Bumble bees Many species of bumble bee (Bombus spp.) are native to North America. Bumble bees forage under more varied conditions than Italian honey bees Bumble bees do buzz pollinate Bumble bees have a longer average tongue length than honey bees (Tuell et al., 2009) Photo credit: fineamerica.com

6 Flower Features For highbush blueberry, the pollination window can be approximately 7-12 days with viable pollen Stigma may be receptive for as few as 5 days under less favorable conditions (Schloemann, 2014)

7 Main Pollination Issues Pollination may be limited by several factors: Floral morphology (Courcelles et al., 2013) Lack of blueberry/honey bee co-evolution Weather Poor hive health genetics, nutrition, pathogens, stress, etc. Recommended honey bee stocking density is 4 hives/a (Drummond, 2012). Photo credit: callonshoneyfarm.wordpress.com

8 Objectives Compare current honey bee stocking densities (~4 hives/a) to high stocking densities (~8 hives/a). Measure the potential benefits of pollination supplementation with bumble bees in commercial blueberry production

9 Methods Both hive density and bumble bee projects were set up the same. With six commercial sites in western Washington in 2016 and High hive density study 3 fields, each with 8 hives/a 3 fields, each with 4 hives/a (control) Supplemental bumble bee project 3 fields, each with 4 hives/a (control) 3 fields, each with 4 hives/a + 3 colonies of bumble bees/ac Mature Duke and Draper plantings Sites were geographically separated 5 mi

10 Methods Measured pollinator activity, as described by Courcelles et al. (2013) Measured activity at % bloom 10 AM to 4 PM; > 65 F N = 30 bushes/site, measured three days legitimate visits Evaluated colony strength by counting number of incoming bees per hive/min for 5, 1-minute periods

11 Data Collected Pollinator visitation rates Hive strength Fruit set Estimated yield Berry size Berry firmness Seed number/berry (Strik et al., unpublished)

12 Hive Strength and Flower Visitation Uniform brood strength was observed in sampled hives Visitation rates were significantly increased Visitation rates, even in high density trial sites, were below recommended thresholds 4 hives/a 8 hives/a

13 Fruit Set and Estimated Yield Fruit set was not significantly different between treatments (data not presented) No difference in fruit firmness was observed regardless of treatment (data not presented) Avg. estimated yield, avg. seed number and avg. berry weight were significantly increased Berry weight Avg. seed (g) no./berry Treatment hives/a 1.4 b 1.6 b 16.8 b 15.5 b 8 hives/a 1.8 a 2.0 a 21.2 a 22.7 a P -value <0.001 <0.001 <0.001 < hives/a 8 hives/a

14 Economic Benefits The average cost for hive rental in 2016 and 2017 was approximately $80 per hive Increased hive density of 10 hives per acre resulted in a net increase of approximately $360 per acre When weather conditions are good for pollination, modest production increases have covered the increased cost of pollination (associated with elevated hives/acre) Additionally, elevated honey bee stocking densities provide a level of protection if weather conditions are poor during pollination

15 Conclusions Increased honey bee hive stocking density increased seed number, berry weight and yield Bees/bush recommendation was not realized even in high stocking density sites Further research and commercial integration require a more reliable source of native Bombus sp. is necessary Point of Interest- We observed a potentially positive relationship between proximity of hives, fruit set, and yield. It is possible that hive distribution, as well as hive density, impact fruit set.

16 Acknowledgments Dr. DeVetter and the small fruit lab Sean Watkinson, Rachel Rudolph, Clara TeVelde and Huan Zhang Grower cooperators Belleville Bees Bee Man Exterminators, LLC Funding: Washington Blueberry Commission Northwest Agricultural Research Foundation (NARF)

17 Thank You!