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Research Project: Colonies in Cold Storage by Examining Relationships among Brood Rearing, Fat Body Metrics & Hours in Cluster to Predict Formation of Winter Bees

Location: Carl Hayden Bee Research Center

Project Number: 2022-21000-022-057-I
Project Type: Interagency Reimbursable Agreement

Start Date: Jun 1, 2023
End Date: Sep 30, 2024

Test for relationships between hours that bees spend in cluster (i.e., when temperatures are < 10 degees C), brood rearing and fat body metrics to predict the formation of winter bees. Objective 1: Measure frames of bees and brood, Varroa mites per 100 bees and Nosema levels from July until December in colonies located in three temperate and two southern U.S. regions. Objective 2: Measure fat body metrics (weight, protein and lipid concentrations) in bees sampled from the brood area from July through December. Objective 3: Test for relationships between hours in cluster and brood area in the colony. Objective 4: Test for relationships between brood area and fat body metrics.

The purpose of this agreement is to improve survival and growth of honey bee colonies overwintered in cold storage by determining when colonies contain ‘winter bees’. From our previous studies with colonies in North Dakota and south Texas, we determined that colonies overwintered in cold storage that contain winter bees (i.e., North Dakota) are larger and have more brood after overwintering than those that did not have winter bees (Texas). Winter bees differ anatomically and physiologically from those in spring and summer. Among other differences, winter bees have larger fat bodies for storing lipids and proteins than spring and summer bees (see Doke et al. 2015, Knoll et al. 2020). In our studies, winter bees had higher lipid to protein ratios in their fat bodies than non-winter bees. The transition from summer to winter bees in temperate regions occurs in the fall and is associated with the cessation of brood rearing (Mattila et al. 2001). Our working hypothesis for the formation of winter bees is that as time in cluster increases in the fall, bees store more lipid in their fat bodies. Increasing storage of lipids in preparation for hive confinement could be linked to the reduction and ultimate cessation of brood rearing since lipids are used for rearing brood (Arien et al. 2020). The combination of bees with high lipid content in their fat body that are not rearing brood are characteristics of winter bees. Determine when colonies contain winter bees and if there is a relationship with ambient temperatures that cause clustering behavior, we will measure colony size and collect bees in three temperate (State College, PA, East Lansing, MI, and Pullman, WA) and two southern locations (Tucson, AZ and Auburn, AL) beginning in late summer (baseline measurements). Hourly weather data will be collected at each site. We will measure colony sizes and frames with brood from July when colonies are actively rearing brood until November or December when colonies have stopped brood rearing. We will sample bees in the brood area during colony measurements and analyze fat body metrics. Analyses will be conducted to test for relationships between hours in cluster (i.e., hours with temperatures < 10 degrees C) and fat body weight and lipid and protein concentrations. If fat body metrics are related to hours in cluster, we should see increasing lipid concentrations and decreasing protein concentrations as hours in cluster increase. We also should see brood areas in the colonies decrease as fat body lipids increase and proteins decrease. The number of hours at or below 10 degrees C required for brood rearing to end will be used as the predictor for the formation of winter bees.