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Research Project: Cold Storage as Varroa Control for Honey Bees in Southern California: Individual- and Colony-Level Effects

Location: Carl Hayden Bee Research Center

Project Number: 2022-21000-022-012-T
Project Type: Trust Fund Cooperative Agreement

Start Date: Jan 1, 2020
End Date: Mar 31, 2022

1. Measure Varroa populations, adult bee mass, brood levels and oxidative stress levels in bee colonies before short-term cold storage, immediately after storage and then at intervals through almond pollination for two groups of hives: one group that will be put in cold storage and another group that will be kept outside as a control. 2. Evaluate bee colony growth and activity by monitoring internal hive temperature and other parameters before, during and after the refrigeration period for both groups. 3. Determine the long-term effects of 4-week cold storage on individual and colony health and subsequent value for almond pollination.

1. Working with a cooperating commercial beekeeper, identify at least 60 colonies, preferably from more than one foraging environment (for example, hives from a commercial agriculture environment as well as hives from a natural forage environment). 2. Evaluate all the colonies to determine adult bee mass, brood levels and food stores (see [8]). Varroa levels will be measured by a) sampling 200-300 adult bees from within the hive and conducting an alcohol wash; and b) placing an adhesive board under the frames in the bottom box to monitor mite fall for at least 2 days. Use those data to divide the hives into groups: one that will be placed in the cold storage warehouse and the other that will not. The average hive strength and Varroa levels should be very similar between the two groups, in order to control for initial conditions. 3. 3 to 4 weeks before the hives are to be put in the warehouse, capture Newly Emerged Bees (NEBs) by placing push-in cages over sections of brood overnight. The next day, 50 NEBs are collected, marked, and released back in the respective hive. Just before the hives are placed in the refrigerated warehouse, as many marked bees as possible are collected from the hives. 10 of the bees will be used to measure oxidative stress markers (protein carbonyl content and malondialdehyde (MDA)) and abdominal dry mass, while 10 will be flash frozen and measured for levels of the vitellogenin mRNA and protein and as well as stress response proteins (superoxide dismutase, glutathione-S-transferase, heatshock proteins 70 and 90). This procedure will be repeated after the hives emerge from cold storage. 4. Sample adult bees from the brood nest during each evaluation, as well as stored honey and pollen. Sampled adult bees are immediately placed on dry ice and brought to the laboratory where they are stored at -80C until they are processed. Honey and bee bread samples are stored at -20 C until they are sent to the National Science Laboratories, USDA AMS, Gastonia, NC for pesticide residue analysis. 5. Install ThermoChron temperature sensors in the top middle of the bottom box of each hive. Temperatures will be recorded every 15 minutes. CO2 sensors may be installed in some hives in both treatment groups, depending on equipment availability. 6. When the warehouse is opened, move half the colonies into cold storage and leave half the colonies at a suitable apiary outside. As a control for hive movement (and not necessarily the cold treatment), the colonies kept in the outside apiary will be moved but then placed into their original outdoor location. 7. After 4-6 weeks, move the colonies out of cold storage. Move control outdoor colonies but place them in their original outdoor location. Evaluate and sample all colonies as in steps 2 and 3. 8. Immediately treat half the colonies in each treatment group against Varroa, to generate a total of 4 treatment groups: 1) refrigeration+ Varroa treat+; 2) refrigeration- Varroa treat+; 3) refrigeration+ Varroa treat-; and 4) refrigeration- Varroa treat-. 9. After 6-8 weeks, evaluate colonies as in step 2. 10. Evaluate and sample colonies prior to almond pollination.