Infections: An Invisible Threat

Joint research on honey bee health in Spain

While the overall beekeeping industry is strong in Spain, the honey bee colonies themselves are frequently weakened by the presence of bee pests and pathogens such as Nosema species. Products to control such pests are not yet readily available. In addition, bee experts suspect that in some regions in Spain the parasitic Varroa mites have become resistant to treatments currently used in the country. This is seen as a rising threat for honey bee health and Bayer is working with Spanish bee researchers to promote healthy hives in the country.

Infections: An Invisible Threat


// Beekeeping and honey production are an important part of the Spanish economy.

// However, parasites and infectious diseases, which are harmful to honey bee health, are increasing and spreading.

// This could lead to economic losses for Spanish beekeepers, unless new strategies to deal with these challenges can be implemented.

// Bayer experts are working with Spanish bee researchers to jointly contribute to the improvement of honey bee health, by strengthening research and understanding of these threats.

Dr Joel González-Cabrera

Dr Joel González-Cabrera
Molecular biologist at the University of Valencia, Spain

Spain is the principal honey producer in Europe: Beekeepers there harvest around 33,000 tons each year for local and export markets. Therefore, beekeeping and honey production are an important part of the economy of this southern European country. However, the sustainability of the beekeeping sector is increasingly challenged because the bees that produce this honey are threatened: "Almost every honey bee colony in Spain is infested with some level of parasites," says Dr Joel González-Cabrera, a molecular biologist at the University of Valencia in Spain. "Beekeepers are tremendously worried about the health of their honey bees because they lack effective strategies to protect them from pests, such as the Varroa mite," explains Dr González-Cabrera. The threat that he and other experts observe: These bee parasites pass on viruses, which weaken the honey bees - and can even be deadly for them.

Renowned researchers, including Dr Mariano Higes, are supporting Spanish beekeepers by analyzing honey bee health. Heading the laboratory of bee pathology at the Centro Apfcola de Castilla-La Mancha, Dr Higes studies bee diseases and their possible causes, and he is concerned about the lack of bee disease awareness: "Many beekeepers don't even know what is wrong with their own bees, as many diseases are almost invisible to the untrained eye." To address this, the Centro Apfcola helps make the correct diagnosis for each diseased beehive: "Local beekeepers can send us bee samples and we examine them to see if they are infected and with what," Dr Higes explains.

Dr Mariano Higes

Dr Mariano Higes
Head of the bee pathology laboratory at the Centro Apícola de Castilla-La Mancha, Spain

However, even bee experts sometimes struggle to give the right diagnosis. In the past, they could not pinpoint the cause of increased honey bee losses which had been seen in some Spanish regions. Initially, farming practices and use of pesticides were among the factors suspected of impacting the honey bees' health. In particular, the neonicotinoid insecticides that had been used on sunflower fields were thought to be the cause. However, not everyone was convinced and so, during his research at that time, Dr Higes looked in more detail at the honey bee loss problem in these regions. "What I found was that the increased mortality rate of honey bee colonies did not occur in regions of sunflower cultivation," he states, summarizing the results of his earlier research. Despite the ongoing debate, he does not believe neonicotinoids to be relevant to the problems affecting Spain's honey bees.

Instead, Dr Higes dealt increasingly with infectious diseases, which are presumed to have the greatest influence on honey bee health. He works closely with Bayer as an industrial partner to not only support beekeepers through research analyses to correctly diagnose the reason for their honey bee colony losses, but to also offer them concrete solutions. "Our collaboration is extremely important, as Bayer might be able to develop bee health solutions based on our research," says Dr Higes. "These solutions may then support us to better control parasites and diseases."


Facts & Figures

Infection doubles and loss rates increase:

Between 2006 and 2015, the Nosema ceranae infection level of Spanish honey bee colonies more than doubled from 40 % to 85 %. During the same period, loss rates of up to 50 % were seen, partly due to Nosema species.

Source: Centro Apícola, Dr Mariano Higes

Bee doctor using a microscope,

Bee doctor: Using a microscope, Dr Higes can see if a bee is infected. Here he is observing the microsporidium Nosema ceranae which is increasingly infecting honey bees in Spain.

"I think that Nosema has become one of the biggest problems for honey bee health in the Mediterranean region, due to a lack of veterinary products to control it."

Dr Mariano Higes

Dr Higes has observed a frequent increase of severe gut infections while examining Spanish honey bees under his microscope. The microsporidium Nosema ceranae is the cause of these intestinal infections. " It is known that this pathogen weakens bees' immune systems, changes their behavioral patterns and shortens their life span," the scientist explains. In the last decade, the number of infected colonies has more than doubled. However, this fungal disease has been underestimated for a long time.
The reason: A closely related Nosema species named Nosema apis was thought to be the sole trigger for nosemosis. It has existed in Europe for a long time already, without being overly harmful for honey bee health. "Host and parasite even seem to have adapted to each other," says Dr Klemens Krieger, Bee Health Expert at Bayer. However, a few years ago, scientists discovered Nosema ceranae, a related type of fungus, originating from Asia. "Unlike with Nosema apis, the Western honey bee has not yet developed any defense mechanisms against Nosema ceranae," says Dr Krieger.

Moreover, this intestinal infection is highly contagious: although a strong honey bee colony may be able to compensate for a certain number of infected bees, Nosema ceranae spreads rapidly due to the bees' social behavior, impacting the entire colony. The infection expands particularly quickly in warmer climates. "Hence, Nosema species have become a fundamental problem in Mediterranean countries," Dr Higes explains. He adds, "In my opinion, it has become the biggest problem for honey bees in Spain." Dr Higes states that 85 percent of the local honey bee population was infected with Nosema ceranae in 2015. Spain's beekeepers are defenseless against the fungal disease as they lack effective treatments. In a joint effort, Dr Higes and Dr Krieger are working intensively to find answers to this problem - hoping to be able to provide alternative treatment options to beekeepers in the future.


A contagious intestinal infection

A single-celled pathogen, invisible to the naked eye, is responsible for nosemosis, the most frequent epidemic infection for adult honey bees in Spain. There are two different species of the microsporidian genus Nosema: Nosema apis has existed in Europe for at least a century, while Nosema ceranae was imported from Asia in the past 20 years.

Honey bees can come into contact with this fungal pathogen through contaminated food or water. Even a small number of Nosema spores can trigger an infection in the bee's mid-gut that weakens the bee. Due to the honey bees' social behavior, the infection can spread rapidly within a weak colony.

Fungal pathogen Nosema ceranae

Highly contagious: The fungal pathogen Nosema ceranae can rapidly spread within a honey bee colony. It weakens the bees' immune system.

Photo Credit: Dr Mariano Higes, Centro Apícola de Castilla-La Mancha, Spain

Dr Klemens Krieger

Dr Klemens Krieger
Bee health expert at Bayer

The experts also collaborate on the control of Varroa destructor with the Veterinary Faculty at the Universidad Complutense de Madrid, where Professor Aranzazu Meana Manes, director of the research group Epicontrol at the Animal Health Department, works. She states: "As in other animal husbandries, medical treatments against bee parasites are only available by prescription. In fact, measures against Varroa in Spain require a treatment in fall that must be prescribed by veterinarians. Therefore, veterinarians play an important role in honey bee health in Spain." The goal of the cooperation of Bayer and the Centro Apícola is to work with veterinarians and involve them in current research, utilizing their expertise to search for suitable treatments and medications.

Dr González-Cabrera is also part of this research network. He is involved in trying to control the Varroa destructor. There are a few treatment options to control the mites and prevent the related disease called varroosis, such as formic acid and synthetic acaricides. Beekeepers from different regions of Spain have been reporting that some products no longer seem to work. According to Dr González-Cabrera, "some mites are no longer controlled by available Varroa treatments - they are, possibly, resistant." Many bee experts in Europe and North America see the Varroa mite as the biggest threat to the health of the Western honey bee.


Most wanted

The Spanish authorities have established a list of bee pests and pathogens against which new treatment options would be required. What are most needed in Spain would be agents to protect honey bees against:

  1. Varroa destructor
  2. European and American Foulbrood
  1. Nosema species
  2. Wax moths

Facts & Figures

65 % of the managed honey bee colonies in Europe are found in the Mediterranean area. Unfortunately, this warm climate region favors the spread of Nosema species.

Source: Centro Apícola, Dr Mariano Higes



Dr González-Cabrera first worked with Bayer when he contributed to a study for three years, looking at Varroa resistance to some synthetic pyrethroid insecticides, in England. He then came to Valencia, Spain, in September 2015 to analyze the worrisome phenomenon of resistant mites via a large-scale study. He explains: "Here in Spain, we also have to find out exactly whether resistance has developed and to establish a monitoring system to evaluate this."


Moreover, in an independent study, he intends to look at preventive measures to maintain the efficacy of the acaricides approved for Varroa control. Concrete information and training courses are being developed to assist beekeepers. 'They should not use active ingredients with the same mode of action for the Varroa treatment in two consecutive years, as this may lead to resistance building up," the expert explains (see also "Combating Varroa" BEENOW 1_2015). Through a rotation of products with different modes of action, beekeepers should be able to avoid resistance.

The list of factors potentially harmful to honey bees is quite long: Pests, diseases, adverse weather conditions, a lack of nutrition and particular agricultural and apicultural practices can all challenge honey bee health. However, Dr González-Cabrera stresses that "most urgently, we need more information about bee pests and diseases." His partners have already initiated important studies on topics including how to survey the development of resistant mites and how to develop strategies for efficient control. With their expertise, these scientists intend to help maintain the economic strength of this leading European beekeeping region. Overall, Dr Higes remains optimistic: "I am confident that we will contain the spread of infectious diseases with intensive research and dialog with other stakeholders involved and restore bee health in Spain."


Guarding the entrance doors against Varroa:
Bayer is working hard to develop solutions to control honey bee parasites.

Bayer researchers have developed a plastic strip containing an acaricidal active substance, which is fitted over the entrance to the beehive and designed to prevent mite infestation. It is planned to bring the product to market in 2017 for use by beekeepers as part of their integrated Varroa management programs.

Varroa diagnosis box

Dr Higes holds a Varroa diagnosis box containing a few hundred bees, taken from a hive. An acaricide kills sensitive mites on the bees and these fall to the bottom of the box where they can then be counted.

Varroa destructor mite

Varroa mites are not much larger than a millimeter, have four pairs of legs, and piercing and sucking mouthparts. The parasite orients itself using numerous sensory hairs all over its body.



Beekeeping is important for the economy in Spain due to the country's extensive honey production. That said, many professional beekeepers see their livelihoods at risk because pests and diseases are threatening the health of their honey bee colonies.

With the strength of shared knowledge, Bayer experts and local Spanish bee researchers are working to address these current problems. They hope to expand their research in the coming years, collect important data about bees pests in different countries and develop new strategies to effectively combat honey bee diseases in Spain.



Bee Health and Varroa Mite

The Varroa mite is one of the biggest challenges beekeepers face in Europe and North America. We explain why this parasite is a major problem for honey bee colonies.


The Western honey bee’s biggest enemy: Varroa destructor

The Western honey bee’s biggest enemy is called Varroa destructor. The mite is a huge threat to the health of the bees as it transmits dangerous diseases.
Bayer expert Dr Klemens Krieger knows the mite well and understands the impact this pest can have on honey bee colonies. In the video he explains how Bayer aims to support beekeepers to protect the bees.


Complete Story

Infections: An Invisible Threat Joint research on honey bee health in Spain

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