Effective Strategies to Control Varroa Destructor Mites

Varroa destructor mites are a serious threat to honey bee colonies. These parasites feed on bee larvae and pupae, weakening the bees and spreading diseases. In this article, we’ll explore their biology, the damage they cause, and effective strategies to control them.

Understanding Varroa Destructor Mites

The Varroa destructor mite is an external parasite that has become a significant threat to honey bee colonies worldwide. These mites originally came from the Asiatic honey bee and have since spread to other honey bee species, including the western honey bee. There are more than 25 different genotypes of Varroa destructor that affect honey bees, each with varying levels of impact on bee health.

Adult female Varroa mites, also known as adult female mite, are oval and flat, red-brown in color, and measure around 1.1mm long and 1.5mm wide. These mites are highly specialized parasites that require a honey bee host to survive and reproduce. The entire life cycle of Varroa mites occurs within the honey bee colony, where they feed and reproduce on larvae and pupae.

Varroa mites have special appendages called peretrimes that help them breathe while hiding in brood food, making them adept at evading detection. They enter the larval cell just before it is capped, lay eggs, and feed on the developing honey bee pupa, which can result in malformation or even death of the larvae.

Varroa mites have been observed spreading not only among honey bees, but also among other flower-feeding insects such as bumblebees, scarab beetles, and flower flies. This indicates their potential impact on various pollinators. This wide distribution underscores the importance of vigilant monitoring and control measures to protect our honey bee colonies from this pervasive pest.

Life Cycle of Varroa Destructor Mites

The life cycle of Varroa destructor mites consists of two main stages: the phoretic stage and the reproductive stage. During the phoretic stage, mites ride on adult bees, feeding on their hemolymph, which is the bee’s equivalent of blood. This stage can last about 5-11 days when there is brood in the colony, but in cold climates, mites may remain in the phoretic stage for 5-6 months if there is no brood.

The reproductive stage of Varroa mites occurs under the capped brood cell. Here are some key points about this stage:

• Varroa mites invade host cells just before they are capped and hide in the brood food.

• Female Varroa mites prefer laying eggs in drone brood due to its longer brood cycle, which provides a more extended period for the mites to reproduce.

• In this stage, a mature female mite can lay five to six eggs in a capped cell.

• The first egg laid is not fertilized and becomes a male.

Varroa mite population growth is influenced by the availability and type of honey bee brood present in the colony. In colonies with brood year-round, the mite population can increase dramatically, whereas it declines by approximately 10% for every month the brood is absent. This rapid reproduction and preference for drone brood make Varroa mites a formidable enemy to honey bee colonies.

Festooning bees in the wild - a common behavior in a healthy bee colony

Impact on Honey Bees and Colonies

Varroa mites have a devastating impact on honey bee colonies. These mites feed on developing larvae and pupae, leading to malformation, weakened immune systems, and reduced lifespans for the bees. The compromised health of the bees affects their foraging and pollination capabilities, which can significantly reduce the productivity of the colony.

One of the most severe consequences of Varroa mite infestations is the transmission of viruses. Varroa mites are effective vectors for viruses such as the deformed wing virus, which leads to crippled and crawling bees. This viral transmission further weakens the bees and contributes to the overall decline in colony health.

The symptoms and effects of Varroa mite infestations are influenced by several factors, including the rate of mite infestation, potential for viral infections, and the honey bees’ natural ability to tolerate Varroa. Severe infestations can lead to Parasitic Mite Syndrome (PMS), a condition that can kill colonies within months of infestation. Additionally, heavy Varroa mite infestations cause scattered brood, impaired flight performance, and lower rates of return to the colony after foraging.

Weakened colonies due to Varroa mites also lead to the spread and invasion of mites between local honey bee populations. This cycle of infestation and collapse in bee hives highlights the urgent need for effective detection and control strategies to protect our honey bees.

Detection Methods for Varroa Mite Infestations

Early detection of Varroa mite infestations plays a critical role in their effective management and control. Various methods, such as sugar shaking, alcohol washing, and drone brood inspection, can help beekeepers monitor and manage mite populations. These techniques are essential tools in the fight against Varroa mites, allowing us to take timely and appropriate actions to protect our honey bee colonies.

Sugar Shake Method

The sugar shake method, a popular technique, provides an effective way to estimate the prevalence of Varroa mites in a honey bee colony. This technique involves:

1. Shaking approximately 200 adult bees into a jar

2. Adding powdered sugar

3. Shaking the bees to dislodge the mites

4. The powdered sugar stimulates grooming behavior in the bees, causing more mites to fall off and be collected on the bottom board.

After shaking, the dislodged mites can be counted on a flat surface. Treatments are recommended if there are 3 mites per 100 bees in the sugar shake or alcohol wash, or more than 30 mites per day on sticky boards. This method is simple, non-lethal to the bees, and provides a quick assessment of mite infestation levels.

Alcohol Wash Method

Another reliable technique to measure Varroa mite prevalence is the alcohol wash method. This method involves shaking approximately 200 adult bees in a jar with isopropyl alcohol, which dislodges the mites from the bees. The mites can then be counted to assess the infestation level.

While the alcohol wash method is highly effective, it results in the death of the sampled bees. Despite this drawback, it remains a valuable tool for accurately determining mite populations and informing treatment decisions.

Drone Brood Inspection

Drone brood inspection is a technique used to monitor Varroa mite infestations by examining drone larvae, which are preferred by the mites. This method involves uncapping drone brood cells and visually checking for the presence of Varroa mites. Since Varroa mites have higher reproductive success in drone brood, this inspection can provide a clear indication of mite infestation levels.

Although drone brood inspection can be less reliable due to variation in sampling, it remains a useful method for verifying Varroa infestations. Regular inspection and monitoring are essential for early detection and effective management of Varroa mite populations.

Source: Agricultural Research Service, the research agency of the United States Department of Agriculture.

Controlling Varroa Mite Populations

Maintaining healthy honey bee colonies necessitates effective control of Varroa mite populations. Various methods, including chemical control options, mechanical control techniques, and cultural and biotechnical approaches, can be employed to manage these pests effectively. Each method has its advantages and limitations, and an integrated approach often yields the best results.

Chemical Control Options

Both soft chemicals, like organic acids and essential oils, and hard chemicals, such as synthetic miticides, are chemical control options for Varroa mites. Soft chemical treatments, such as oxalic acid and thymol, are preferred in integrated pest management (IPM) before considering hard chemicals. Oxalic acid is especially effective during broodless periods and can reduce mite populations by up to 90% if applied during a cold winter.

Thymol, derived from thyme, can control mites on adult bees but does not penetrate cell cappings. Formic acid, another soft chemical, can penetrate wax cappings and kill reproducing mites, although its efficacy is temperature-dependent. These treatments offer sufficient efficacy with low risks of residue accumulation and resistance in the mite population.

Hard chemical treatments, such as amitraz, fluvalinate, and coumaphos, are used as a last resort due to potential resistance and residue issues. Synthetic chemicals are not recommended as the first choice because they can harm bees directly, make them more susceptible to diseases like nosema, and leave residues in bee products. Rotating treatments is beneficial to prevent resistance and maintain effective control.

Mechanical Control Techniques

For Integrated Pest Management (IPM) of Varroa mites, mechanical control techniques constitute an essential component. There are several methods used, such as screened bottom boards, drone brood removal, and powdered sugar dusting. These methods help to manage and control the bee population effectively. When using screened bottom boards, mite invasion into brood cells is reduced, leading to a lower percentage of the population reproducing in the brood. This makes them effective in managing mite infestations.

Drone brood removal exploits the mites’ preference for drone brood, using it as a trap to reduce the final mite population by 50 to 70 percent. This technique takes advantage of the higher reproductive success of mites in drone brood due to the longer post-capping period, allowing beekeepers to manage mite populations more effectively.

Cultural and Biotechnical Approaches

Sustainable options for Varroa mite control are provided by cultural and biotechnical approaches. These methods include using mite-resistant honey bee stock, small cell comb, and providing a brood break. Mite-resistant bees, such as those with Varroa sensitive hygiene (VSH) traits, can detect and remove infested brood, limiting mite reproduction.

The use of small cell comb is debated, but it does not harm honey bees and may contribute to controlling mite populations. Providing a brood break interrupts the mites’ reproductive cycle, reducing their numbers. Additionally, research into probiotics aims to improve bee health by enhancing their resistance to pathogens and parasites.

Projects investigating the benefits of probiotics involve isolating beneficial bacterial strains and applying them to bees to measure their impact on physiological and immune parameters. These innovative approaches offer promising avenues for enhancing the resilience of honey bee colonies against Varroa mites.

Integrated Pest Management (IPM) for Varroa Mites

With minimal pesticide use, Integrated Pest Management (IPM) offers a holistic approach to managing Varroa mites. This strategy combines various control techniques throughout the year to reduce resistance and maintain healthy honey bee colonies. Monitoring varroa mite levels regularly is crucial for determining the need and type of treatment to use.

In an IPM approach, treatments should be rotated to prevent resistance, and economic thresholds aim to keep mite levels around or below a mean abundance of 2 mites per 100 bees. This helps ensure that treatments are applied only when necessary, reducing the risk of resistance and minimizing the impact on bee health.

Managing viral infections within honey bee colonies is also a key aspect of IPM. Beekeepers can prevent colony collapse by maintaining low mite populations, as exceeding certain threshold levels can be detrimental to the colonies. Keeping a check on mite populations is crucial for the well-being of the bees. This integrated approach provides a sustainable solution for long-term Varroa mite management.

Timing and Frequency of Treatments

In the effective control of Varroa mite populations, the timing and frequency of treatments are critical factors. Controlling mites in the fall is particularly crucial as it is linked to the overwintering survival of honey bees. Beekeepers must be diligent, as failing to manage Varroa mites can lead to significant losses, with some reporting up to 30% hive losses during winter.

Spring and winter treatments are deemed the most important by many beekeepers. Spring treatments ensure low mite infestation after winter, helping bees during the busy spring and summer periods. Winter treatments aim to significantly reduce mite populations, protecting the last few brood cycles needed for a successful colony over winter. The recommended timing for applying a chemical miticide is prior to the production of winter bees.

During summer (June to August), colonies should be checked monthly for mites, but treatments should avoid periods of honey flow to prevent contamination of honey. In the fall (September to November), colonies should be sampled every three weeks if weather permits, and treatments should rotate miticides to prevent resistance development. Winter monitoring with sticky boards minimizes disruption of the winter cluster.

Varroa mite levels should be regularly monitored at least four times a year. These monitoring times include:

• Early spring

• During the spring/summer honey flow

• After the last honey flow

• Late autumn before the winter pack-down

This consistent monitoring and timely treatment application help maintain healthy colonies and prevent mite populations from reaching damaging levels.

Speaking of autumn, our bees make some delicious Autumn Honey!

Lessons from Global Experiences

Valuable insights for beekeepers worldwide are offered by global experiences in managing Varroa mites. In Australia, significant efforts are underway to help beekeepers manage Varroa mite infestations. Regular hive inspections are critical to determine the spread of Varroa throughout the country or to detect new incursions. This proactive approach helps in early detection and timely intervention, preventing large-scale colony losses.

The UK has also provided key lessons for managing and controlling Varroa mites, emphasizing the importance of effective management options. In countries where Varroa has been present for a long time, control varroa mites methods focus on determining mite levels within the hive, when to treat, and assessing treatment success. These practices highlight the necessity of regular monitoring, timely treatments, and adapting strategies based on local conditions.

Learning from these global experiences can help beekeepers implement more effective Varroa mite management practices. By adopting proven strategies and staying informed about new developments, beekeepers can better protect their honey bee colonies from this persistent threat.

Future Directions in Varroa Mite Research

Future research in Varroa mite control is centered around enriching our understanding of honey bee immunity, physiology, and the impact of parasitism. Researchers like Pavel Hyršl, who received the 2023 MUNI Innovation Award, are studying the immunity, longevity, and parasitism impact on honey bees. This research aims to uncover new ways to enhance bee health and resilience against Varroa mites.

The Laboratory of Comparative Immunology at the Department of Experimental Biology is also making significant strides in studying insect immune systems, including honey bees. Their research focuses on the physiological and immune reactions of bees when attacked by Varroa mites and associated pathogens. By understanding these interactions, scientists hope to develop more effective strategies to protect bees from mite infestations.

Current studies employ the OMICs approach to assess overall changes in gene activity and protein/metabolite spectra in bees impacted by Varroa mites. This comprehensive analysis provides insights into how parasitism affects bee health at a molecular level, paving the way for new treatments and preventative measures.

Additionally, developing new bio-pesticides and probiotics is a promising area of research. These innovations aim to improve bee health by enhancing their resistance to pathogens and parasites, offering sustainable solutions for Varroa mite control.

Continued research and development in these areas will be crucial for the future of beekeeping and the protection of adult honey bees, asian honey bee populations, european honey bees, and other honey bee species.

Experience From My Own Honey Bee Colonies

I am a slow learner. I was really against using any sort of chemical treatments in the hives until I decided to learn more about what each treatment does for the bees and their health. Mites are the issue. So, they need to be eradicated

In a conversation with the man that I buy my bees from when I first began my beekeeping journey, he said to me, "Get your mite-away strips on before mid-August." I said, "I usually do that around the end of October." He replied, "If you wait until the end of October, then I will see you again in April for new bees."

I decided to order the mite-away strips and treat the bees in August. We now do this treatment in June after the first honey harvest. Mite-Away Quick Strips are made with formic acid. Formic acid is a compound that is naturally found in the hive and is the bi-product of insect bites and stings. It is proven to be effective against varroa mites. This product should. not be used in temperatures over 85 degrees and the treatment stays in the hive for only 5 days.

The next step in treating the bees involved vaporizing oxalic acid. Oxalic acid is an organic compound found in leafy greens. The way it works is to treat every 5-7 days or as our schedules permit for three cycles. Unfortunately, I lost almost every single hive two years in a row using this technique, and will never use it again.

The method working best for me is to use the formic acid pads and the mite-away pads while also adding the screened bottom board. So far, so good.

Save the Honey Bees

Effective management of Varroa destructor mites is essential for maintaining healthy honey bee colonies. Understanding the life cycle and impact of these mites on honey bees and colonies allows beekeepers to implement targeted control strategies. Detection methods such as sugar shaking, alcohol washing, and drone brood inspection are vital for early identification and management of mite infestations.

Various control methods, including chemical, mechanical, and cultural approaches, offer different advantages and limitations. An integrated pest management (IPM) approach, combining these methods, provides the best results by minimizing pesticide use and resistance. Regular monitoring and timely treatments are crucial for keeping mite populations below damaging levels and ensuring the survival of honey bee colonies.

Drawing lessons from global experiences and staying informed about future research directions can help beekeepers enhance their Varroa mite management practices. By adopting proven strategies and remaining vigilant, beekeepers can protect their hives and contribute to the sustainability of honey bee populations worldwide.