Investigating the impact of honey bee wintering method on hive health and cause of death

Commodities

Practices

Investigating the impact of honey bee wintering method on hive health and cause of death

High winter loss rates of honey bee hives are becoming increasingly frequent to an extent that threatens the sustainability of the beekeeping industry, causing concerns for the ability of beekeepers to make a profit and provide pollination services to farmers. Four of the six US states that experienced loss rates above 65% during the winter of 2024-2025 are in the North Central Region.

Wintering bees in indoor, temperature-controlled buildings leads to higher hive survival and success. However, it is not well understood why indoor wintering benefits honey bees. Crucially, the difference in when and how hives die in outdoor and indoor wintering has not been evaluated. If we are to address and mitigate overwintering losses, it is imperative to have a deeper understanding of the causes of winter death, and how indoor wintering can reduce sources of mortality.

Additionally, the economic viability of indoor wintering has only been evaluated for large-scale commercial beekeepers. Thus, there remains a large sector of beekeepers continually suffering high overwintering losses that are missing key information regarding a possible solution to wintering mortality.

To understand what drives differences between outdoor and indoor wintering, a group of hives will be wintered in a typical outdoor set up while another group will be wintered indoors. Both groups will have internal sensors and scales deployed in order to receive constant data on the hives' ability to thermoregulate, available honey stores, and brood rearing. Additionally, dead bees will be collected from live hives throughout the winter to test fat body size and sample for fungal and viral infections. Hive survival will be tracked, and after a hive dies it will immediately be "autopsied" to determine cause of death.

Beekeepers will be surveyed to gauge their most prevalent issues with wintering, how much they spend on wintering, and their interest in indoor wintering. Then, we will offer an indoor wintering outreach event for beekeepers and survey them again.

The outcomes of the study will be a greater understanding of the causes of wintering mortality for indoor and outdoor wintered hives, an economic analysis of the two wintering methods, and a webpage with outreach materials for beekeepers that help them to understand winter mortality in their own apiaries and the management options they may use to improve wintering success.

The goals of the project are to understand what causes hive death for indoor and outdoor wintered hives, to compare the economic viability of both options, and to help beekeepers make informed decisions about what wintering techniques to use in their operations. The outcomes related to these goals are focused on relaying our results to beekeepers and creating resources to aid beekeepers in management decisions that impact overwintering success.

A webpage regarding overwintering will be added to Iowa State University's Bee Program website (https://bees.cals.iastate.edu/). The webpage will provide information about indoor wintering, resources for completing hive autopsies, and interactive decision support tools; where beekeepers can input results from hive autopsies and receive advice on management techniques and economic costs and benefits associated with each technique.

In person events will include an outreach event intended to expose beekeepers to indoor wintering and presentations at local beekeeper meetings.

Learning outcomes for involved beekeepers will be how to improve wintering success, how to use indoor wintering, and the economic costs associated with indoor and outdoor wintering techniques.

Action outcomes will include a decision to look into indoor wintering, changes in outdoor wintering practices, and the use of hive autopsies to understand causes of death in their own hives.

Outcomes will be measured using survey results from before and after our outreach event. Our overwintering webpage will be promoted during in person events and we will measure the impact of the webpage by looking at the number of visits the site receives.