Wintering Honey Bee Colonies With & Without Upper Entrances:Comparing Internal Temperature, Humidity, Food Consumption, Spring Cluster Size & Survival

Progress report for FNE23-061

Project Type: Farmer
Funds awarded in 2023: $7,035.00
Projected End Date: 04/30/2026
Grant Recipient: Musante Farm
Region: Northeast
State: Massachusetts
Project Leader:
Amy Musante
Musante Farm
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Project Information

Project Objectives:

This project seeks to compare honey bee colonies wintering with and without notched inner covers as upper entrances. The specific objectives are to assess the impacts on:

1) internal hive temperatures

2) relative humidity within the hive

3) winter food consumption

4) spring cluster size

5) over-winter survival

These data will allow us to assess the potential costs and benefits of having an upper entrance and ventilation in a cold winter climate. The humidity sensors will provide relevant data with regards to the common belief that without an upper entrance the hive will become too humid and the moisture will condense out and rain down on the bees. This study will allow beekeepers to make an informed, data-based decision about whether to use notched inner covers as upper entrances, rather than simply basing the decision on common practice and theory. If the results support the suspected detrimental impact on wintering colonies, this study has the potential to modify a common management practice and thereby help increase winter survival in cold climates.


Honeybees are essential to the US agricultural system, with the majority of crops requiring extensive pollination services (Chopra et al 2015). Farmers in the Northeast rely on honeybee pollination for important crops such as blueberries, cranberries, and apples, among others. While the demand for US pollination services has increased, colony survival has continually decreased in managed honey bee colonies (Bee Informed Partnership 2008 - 2021). Year after year, the northeastern states represent some of the highest losses in the country (Bee Informed Partnership 2008 - 2021). Last year, the combined winter losses for New England states averaged over 45% (Bee Informed Partnership 2021)! My tiny state of Massachusetts alone brings in well over 10,000 packages of bees annually (Skrym, 2020). This amounts to hundreds of thousands of dollars, without even considering the costs of replacement queens and more expensive nucleus colonies. Of course, bee farmers must also pass some of these costs on to the farmers with pollination contracts. Consequently, the annual replacement of so many colonies is enormously costly for farmers in the northeast region.

The obvious approach to this problem is to reduce the need for colony replacement by increasing the survival of existing colonies. Any improvement in successful over-wintering will significantly increase a farm’s net income, since each colony replacement removes several hundred dollars from their bottom line.  What’s more, unlike newly established replacement colonies, which typically require a full season to get up to strength, colonies that survive the winter are also capable of generating a honey crop and/or being split to create additional colonies. Surviving colonies generate significant income for farms.

The extreme winter losses provide beekeepers an opportunity to reassess management practices to determine if anything can be done to improve management protocols and increase winter survival. Last winter a significant proportion of colonies were lost during a single week of particularly cold weather (pers. obs. 2022) This observation caused me to look into the thermodynamics of wintering hives. This literature search led me to the discovery that a very common wintering management practice may well be playing an important role in overwinter colony loss (Mitchell 2017)

During the cold season, it is customary for northeast beekeepers to utilize a notched inner cover. The reasons given for doing this are to provide an upper entrance and more importantly to allow excess moisture to escape so it does not condense out and rain down on the bees. I have reason to believe that this practice is negatively impacting winter colony thermodynamics and may well be contributing to exceptionally high winter losses in our region. Given the extreme variation in microclimates and beekeeping husbandry, the presence/absence of an upper entrance must be studied side by side in the same location. To my knowledge this has not been done. Given the simplicity of changing this management practice, this study has the potential to make a significant contribution to the beekeeping and farming community.


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  • Dr. Robyn Underwood - Technical Advisor


Materials and methods:

Since this project involves comparing colonies wintering with and without notched inner covers as upper entrances it is imperative that the colonies in each group are matched for hive configuration, bee population, and colony weight (a measure of food stores).


The first step involves identifying matched pairs of colonies. Each pair must be matched for hive size (8 Frame or 10 Frame), number of medium hive boxes, and bee population (as determined by “frames of bees” at a time when foragers are present).  Once 10 pairs of colonies have been identified, each of the colonies in each pair will be randomly assigned to treatment group using a random number generator.



DETERMINING SENSOR PLACEMENT: A total of 80 dual temperature & humidity Broodminder brand sensors are available for use in this study.  The fall/winter of 2023-24 is being used to practice data collection, uploading, and more importantly to establish the most useful sensor number and placement for each colony size.

All of the sensors and data collection/uploading methods will be tested prior to the official start of data collection.  The temperature/humidity sensors will be placed above frame number 5 in the top two boxes of each colony.  Official sensor data collection will begin on 11/02/2025 at 12:01am. The sensors will document the internal hive temperatures and relative humidity at the installed locations for each colony.  Official sensor data collection will end on 4/01/2026 at 11:59pm



ASSESSING WINTER FOOD CONSUMPTION: All colonies will be weighed on 11/1/24 and 4/1/25 in order to determine approximate winter food consumption. 




Spring Colony Strength Assessment 1 (preliminary): on a weather convenient day in March 2025, a preliminary cluster size assessment will be made by examining the chewed cappings on screened bottom board inserts.  This is only an approximation of cluster size and will only provide preliminary information.  All bottom boards will be replaced with new inserts on the same weather convenient day of the month.  Exactly 1 week later they will all be removed, photographed and assessed for cluster size.

Spring Colony Strength Assessment 2 (final): On the same weather convenient day in April all colonies will be officially assessed for cluster size, by opening each hive and directly assessing the cluster size at a time when foragers are inside the hive.  Clusters will be estimated by counting the frames of bees in each box.  No smoke will be used until such assessments have been made.



WINTER SURVIVAL:  All colonies will be monitored throughout the winter for signs of life.  These signs include bees observed at entrances, dead bee removal, cleansing flights, and chewed cappings from brood/food. If colonies are presumed dead that date will be recorded and last confirmed active will also be recorded.  All colonies surviving on April 15, 2025 will be considered to have survived the winter.  The sensor temperature data will also provide empirical data on the actual date of death. The reason for collecting observational data is to verify its usefulness for non-study related teaching purposes.

Research results and discussion:

2023-24 EXPLORATORY PHASE PRELIMINARY RESULTS: For the pre-experimental phase, 5 pairs of colonies were matched for size and strength in September 2023.  These colonies cover a variety of hives sizes (8 frame and 10 frame) and configurations (3, 4 and 5 boxes).  This important phase was added in order to determine the best sensor placement prior to the official start of data collection next winter.  In November 2024, once the outside temperatures suggested that the main robbing season was over, the dual temperature/humidity sensors were placed above frame number 5, in the top two hive boxes of each colony.

After practicing data uploading and studying the preliminary data, it appears that in some colonies, the bees are clustering in boxes below the sensors, especially in the larger hive setups.  Rather than moving one or more of the sensors to lower boxes, we decided it would be more useful to order and install additional sensors in the lower boxes.  This should allow us to determine if we can maximize treatment size by installing a sensor in every other box, or if instead we will need a sensor over every box for the study. The ability to study and modify sensor placement will allow us to fine-tune the protocol in order to collect more meaningful data once the official study begins next fall.

Participation Summary
1 Farmers participating in research
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.