• Fr
  • En
  • Es

Winter colony losses. Can we do something about it?

Table of contents

Winter is when most of the honeybee colony losses occur. Bees enter a phase where they must rely on their stored food reserves. Weeks before, still in autumn, is when the winter bee is developed, requiring larger fat bodily reserves, and thus, any malnutrition will have consequences on the winter population. But this is mainly the period when poorly controlled varroa infestations and viruses carried by the mite will cause hive collapse, and when Nosema ceranae infestation often shows, leading to depopulation.

The end of the productive season is a time to evaluate how we performed.

Crunching the numbers: a deep dive into bee colony statistics

The Bee Informed Partnership platform annually publishes colony loss results in the United States. Through their network, which includes collaborating beekeepers and The Apiary Inspectors of America, they survey over 3,000 beekeepers managing 314,360 colonies, representing 12% of the estimated 2.7 million colonies in the US.

The preliminary data for the 22-23 season is not favorable. They’ve estimated around 37.4% loss during winter, a significant increase compared to the 24.2% Winter ‘21-22 loss. 

Let’s not forget that bees in the US are responsible for pollinating over 100 different crops.

Although beekeeping companies can bear such losses and remain profitable, it is a situation that should not be, not only for the losses of animals and their economic value, it’s also the risk for agriculture that the loss of pollinators entails. As beekeepers, veterinarians and other consultors we must ask ourselves what is happening to try to correct the situation. But, can we really do something about it? Let’s wonder what’s going on:

What are the causes that beekeepers have observed?

US beekeepers attribute the losses to varroa mite infestation during winter and queen failures in the spring, with adverse weather conditions coming in a close second. Annual losses were higher among backyard beekeepers at 54.6% compared to 47.9% among professionals, this is surprising as one of the major challenges in beekeeping is the time required for monitoring and treating varroa, more limited for those beekeepers who manage thousands of hives across states compared to those who engage in beekeeping as a leisure activity. Higher losses between hobbyists compared to professionals attributed to the beekeepers’ ability to recognize signs of infestation earlier and take timely action.

Formation & information dissemination among beekeepers

Some commercial beekeepers take advantage of the Bee Informed tech transfer teams for monitoring and advice, but many do not use the service. Hobbyists and non-commercial beekeepers are largely on their own. Information and protocols are available but not always used.

How are beekeepers facing varroosis infestation? Are they implementing new strategies? Are they adapting practices and routines?

Managing varroa is one of the most decisive factors but it’s not easy, it requires a large amount of experience and commitment to control the parasitic infestation.

To control varroa is very important management; in every beekeeper’s visit detection protocol should be emphasized, involving:

  • Frequent brood chamber inspection,
  • Sampling nurse bees in at least 10% of the hives in an apiary (or even 25% to all hives for smaller apiaries),
  • Varroa monitoring with alcohol wash, sugar roll or CO2 injection to obtain a representative infestation rate (alternatively, you can also count the natural mite fall on sticky boards, but this is mostly done in Europe).

Based on the data, the decision to treat or maintain surveillance can be made. Can we confidently assert that sufficient time is being dedicated to varroa assessment?

It’s possible that hobbyist beekeepers decided to keep bees before receiving adequate training, thus lacking the skills or information to monitor or treat varroa. And for commercial beekeepers it just takes too much time when they are managing tens of thousands of hives.

Programming control involves incorporating sampling materials into regular apiary visits, recording data, and keeping records before, during, and, more importantly, after treatments. Only registered treatments should be used, and preparations without a scientific basis or whose toxicity has not been proven by the authorities should be avoided.

It also implies vigilance over reinfestations. Without such parasite monitoring, beekeepers might mistakenly believe that the varroa infestation is at a much lower level than it is.

Is V. destructor changing to more pathogenic?

Some beekeepers believe that varroa mites have changed their habits in recent decades, appearing to hide better between the abdominal plates and not being as exposed as before on the bees’ backs. If beekeepers only rely on detecting the mite with the naked eye, they will be missing quite a few of them. But also, the participation of viruses plays a large role in colony losses.

In year 2000 writing in Mites of the Honey Bee, Mike Hood & Keith Delaplane wrote a 300 bee sample calls for treatment at 15 mites in a 300 bee sample justify treatment, that’s a 5%. Today the Honey Bee Health Coalition current thresholds state a maximum of 3 mites per 100 bees.

Do warmer temperatures represent a threat?

The effect of climate change, especially frequent droughts, and increasingly intense heat waves, has a clear impact on bees. Colonies’ nutrition is severely affected in various ways: qualitatively due to biodiversity loss and quantitatively because the produced pollen and nectar have a much lower nutritional value. Climate change and exposure to monocultures make hives much more dependent on quality supplemental feed. Supplementing with sugar syrups will be just for a few specific situations. Now discussions revolve around protein-rich foods, vitamin supplements, probiotics, and prebiotics to enhance bee immunity.

We are beginning to understand the importance of the microbiome, the beneficial bacteria in the bee intestine provide a barrier against infections such as nosema or viruses. This protective partner benefits from natural feeding, however, the abuse of feeding only based on syrups and especially the use of antibiotics impoverishes its wealth, negatively affecting the health of the bee.

With such dramatic changes in the natural environment, the same nutritional management practices are not enough.

Higher temperatures undoubtedly influence bee colonies, such as prolonged brood presence, that favors parasite development while complicating disease management as most acaricides have a poor effect through the operculum. Beekeepers must anticipate this situation and be able to deal with warmer springs involving more brood, perfect conditions for varroa development, and extreme heat and drought in summer causing nutritional stress.

Again, with changing conditions, we must anticipate the problems that will come.

Any other possible causes?

US heavily relies on bees for crop pollination, with the Agricultural Research Service estimating that bee pollination adds at least $18 billion to total agricultural production, honey production in the US is secondary.

In America, hives are more exposed to agrochemicals—a risk in itself for survival. Additionally, monocultures cause an unbalanced protein intake, necessitating supplementary feeding. Nutrition stress causes depopulation and increased susceptibility to disease.

In other countries, there are disparate situations. While in Chile or Argentina they have losses similar to the US with 53 and 34% respectively, in Europe the losses range between 20% in Spain and 15% in Germany or France. New Zealand’s annual bee colony loss survey reported losses of 13.59% for 2022, this figure is quite remarkable considering their beekeepers also move thousands of hives. Probably their collaboration with Australia (one of the few countries free from Varroa destructor, until recently) has paid off.

Are the countries with lower losses doing things any differently?

Basically, the fight against the parasitic mite is based on monitoring and anticipation for when parasitism (the presence of a parasite without interfering in the life of the host), becomes parasitosis, the parasitic disease.

Understanding the multiple factors that influence is complex. The causes contributing to the colony mortalities are only beginning to be understood, especially factors like the sublethal effects of neonicotinoids or the role of Nosema or infectious diseases like foulbrood. Various factors, while not the primary cause of loss, can add up to the problem.

We have tried to review the main causes to our knowledge, which can be decisive in the loss of bee colonies. Nutritional stress, environmental toxicity, and the evolution of a parasitic disease that demands increasing attention, time, and money are three key points to emphasize. Given the lack of a definitive solution against the parasitic mite, the increasing presence of pathogens and predators affecting bees globally, and the impact of various environmental factors causing stress on colonies, beekeepers’ vigilant attitude is becoming increasingly indispensable. Support from specialized technicians is crucial to ensure a beekeeping stock capable of meeting our crop pollination needs and producing quality food.

There is a second reading in these data, as bees are biomarkers. Colony losses suggest that at the same time, we are losing other wild pollinators equally essential for the conservation of biodiversity.

About the Author

Juan Molina is a veterinarian from the Universidad de Córdoba with specialization in beekeeping from the Universidad Complutense. Deeply passionate about apiculture, he’s affiliated with the Asociación Malagueña de Apicultores and has authored two books on the subject. Juan’s roles have ranged from Quality Manager for honey to imparting courses for bee enthusiasts. He’s also a recognized speaker at beekeeping conferences.