The honey bee industry has recently faced extraordinary challenges for the last few years. One of these is Varroa destructor, a parasite that can weaken and kill bee colonies in just a few months.

Unfortunately, breeding honey bees is not as easy as some think. Bees are fundamental to our ecosystem, and their decline has severe implications for all of us. Breeding bees requires constant vigilance and a healthy respect for the environment of the hive and its inhabitants. If you are thinking about beginning beekeeping as a hobby, or even if you are a novice beekeeper looking to improve your breeding standards, this guide is an indispensable resource. In this article, with the help of the experts from the OXALIKA team, we will cover everything there is to know about the varroa mite, including the threats to your hives, how to protect them, and what measures you can take.

What is Varroa?

As we have anticipated, Varroa destructor is a parasitic bee mite that feeds mainly on the fat body of bees (source: https://www.pnas.org/doi/10.1073/pnas.1818371116) and perhaps also on their hemolymph, causing many problems for the colony. Varroa is harmful to honeybees because it reproduces in the larvae cells and can spread quickly in your apiary.

Varroa and honey bees: an overview

Honey bees live in colonies with several thousand insects; they are very social insects. The worker bee is the most common insect in the colony. The primary responsibilities of a worker bee within the colony include:

• Collecting nectar to make honey.
• Providing care for the larvae.
• Tending the hive.

This specialized bee tirelessly works until they die about six weeks after leaving the cocoon as adults. The queen bee usually lives up to three years and produces hundreds of thousands of eggs during her lifetime. Varroa attacks all types of bees and broods. Especially in the larvae, Varroa causes enormous damage, causing malformations and blocking the development of individuals. The damage made by Varroa is due to its parasitic action. Varroa is an “ectoparasite” that feeds mainly on immature and adult bees’ fat bodies and hemolymph. Varroa also produces behavioral altering effects in adult individuals and reduces biological functions. These issues can quickly collapse the colony if you don’t promptly take action.

Why does Varroa attack honey bee colonies?

Varroa attacks the bees to feed on them and to be able to reproduce. If not adequately treated and controlled, Varroa can quickly spread from one hive to another and can kill an entire apiary in just a few months. Varroa-infested bees are more vulnerable to disease and less likely to survive the winter.

Varroa: main symptoms of the infestation

Varroa can cause several symptoms in infected bees, including bee weakness, deformation of the wings, a behavioral disorder in the hive, and increased mortality.

Primary symptoms of Varroa destructor infestation:

In adult individuals

• Deformity on the wings and atrophy;
• Presence of adult mites on the body of bees;
• Reduction of abdominal mass and volume.

In broods

• Broods with altered, non-compact structure;
• Caps that have holes or are heavily damaged;
• Presence of dead or deformed bees in the brood;
• The apparent presence of brown or immature white-colored adult mites;
• Dead, dry larvae.

For more detailed information on the symptoms of varroatosis (varroa infestation), it is possible to consult the appropriate section of the U.S. Agricultural Research Service website or your local equivalent.

How to recognize Varroa in the hive?

It is essential to carefully examine the bees and their nests to recognize Varroa in hives. Varroa is a parasite that attaches to bees and may be visible to the naked eye as a small, round, oblong brown or white body on the bee’s back. Other symptoms to look for are bees with deformed bodies or short, rough wings. Varroa-infected bees may also exhibit signs of debilitation, such as apathy, lethargy, and lack of coordination.

Test for the presence of Varroa with powdered sugar

What is needed

• White container;
• Honey pot with 2mm grid;
• Tablespoon;
• 100ml container;
• Powdered sugar.

How to proceed

Place a frame containing the brood vertically above the hive. Pass the 100ml container by sliding on the back of the bees, gently moving from top to bottom so that they will fall into the container. Be careful not to take the queen. When the bowl is full, you will have collected about 300 bees. At this point, you can transfer the bees into the honey jar, adding one tablespoon of powdered sugar. Close the honey pot with the grid cap and mix gently, careful not to spill the sugar. When finished, let the honey pot with the bees and the icing sugar rest for about a minute. Next, shake the honey pot over the white bowl for about a minute. To count the Varroe more efficiently, you can put a little water in the container. The water will dissolve the sugar and help you identify and measure the number of mites. At the end of the procedure, you can free the bees in their hive.

To determine the level of infestation as a percentage, divide the number of mites by three, e.g., 21/3 = 7, which corresponds to 7% of Varroa. If the average percentage of varroa in the colonies of the apiary is about 2%, You should treat it within one month. If the value reaches 5%, it is necessary to treat the colony immediately to try to save it.

Test for the presence of Varroa by natural fall.

The natural fall test is a simple method but with some limitations. For example, it cannot provide accurate information on the future course of the infestation. The results are reliable only in the presence of broods and are not reliable when the collapse of the family due to the infestation is already underway. Furthermore, this test can be carried out only in hives with an anti-varroa bottom.

The accuracy of this test can increase as a function of the observation period. An optimal duration can be as much as one or two weeks.

How to proceed

• Place a sheet of oiled paper or an adhesive on the bottom of the hive.
• Leave the sheet for the entire duration of the observation (minimum of three days)
• At the end of the observation period, divide the number of mites found by the number of observation days to get an idea of the daily fall.

For observation periods longer than three days, it is advisable to repeat the test several times (every three days) to prevent the ants from taking away the fallen mites.

Thresholds to be taken into consideration

• Over eight mites a day: immediate treatment
• Two mites per day: treat within two months
• Over one mite per day: treat within three months and in any case before winter.

(source: https://www.researchgate.net/publication/41712276)

How Varroa spreads and affects bees

Varroa spread mainly through bee larvae and their nests. Parasites are transferred from infected bees to larvae during egg-laying. Varroa reproduces in the brood cells of bees. Mature female mites (also called mother or founder mites) enter the cells shortly before they are sealed. The founder begins feeding on the brood within six hours of the cell being sealed. The part of the larva where the founder pierces the cuticle to feed becomes the main feeding area for her offspring.

The life cycle of the Varroa Destructor mite

The first egg laid by the founder varroa will become a male. The second egg will become a female mite which will mate with the male. The founder mite feeds on developing larvae and can transmit viruses to bee larvae. Finally, when the bee is fully developed and emerges from the cell, the founder mite, and its children appear and attach themselves to the adult bees. Varroa on adult bees is called a “phoretic mite.” Most commonly, phoretic mites attack the young bees that develop the brood. The phoretic mites target these bees because they usually remain in the brood area and can act as a vehicle to transport Varroa between cells in the brood. Phoretic Varroa can feed on adult bees, but when a brood cell is found ready to be closed, the mite will detach from the bee and enter the cell to reproduce.

(source: https://www.ars.usda.gov/)

Treatments against the Varroa of bees

The treatments against Varroa are different and depend on the situation of the hive. Suppose you detect the presence of Varroa in your hive but not in sufficient quantity to cause problems. If so, we recommend that you continue to monitor the trend to be able to intervene appropriately at the appropriate time. However, if Varroa is causing problems in the hive, it is essential to take action with proper treatment.

Chemical and pharmacological treatments:

The most efficient treatment against Varroa is vaporization with oxalic acid. Other therapies include the use of different products:

• Thymol-based products (e.g., Apiguard);
• Strips based on fluvalinate (e.g., Apistan), the active ingredient, fluvalinate, works by destroying the nervous system of mites and has low toxicity on bees;
• Pesticides based on Formic acid (e.g., Mite Away) are very effective because they reach and kill the Varroa during reproduction inside the closed cells. However, formic acid is only effective at temperatures above 50F. Therefore this treatment is not indicated during the winter or in frigid climates.

(source: https://extension.psu.edu/)

Oxalic acid is the most efficient treatment in terms of costs and benefits. Varroa can also quickly develop resistance to fluvalinate. For now, Varroa does not appear to have developed resistance to oxalic acid, but to avoid this, we recommend rotating the different treatments regularly.

Please pay attention! Treatments with specific chemicals, drugs, and pesticides are subject to limitations and restrictions depending on your country. Always use personal protective equipment such as gloves and masks when working with anti-parasitic drugs and avoid contact with mucous membranes and skin.

Steps to take to combat Varroa

1. Continuously pinpoint and monitor the infestation. The first step in fighting Varroa is to monitor the colonies constantly. The monitoring can be done by checking the bees regularly and inspecting the hive for signs of infestation. Beekeepers generally measure the number of mites present per 100 bees at regular intervals (e.g., monthly) to determine when the mite population on adult worker bees exceeds a certain threshold. This control can be done with several methods, including the use of powdered sugar, rinsing with alcohol, or applying a thin layer of vaseline to a diagnostic drawer. This way, the varroa that falls on it will remain attached and not be carried away by the ants. The action of the ants could slant the count of the fallen varroa.
2. Chemical and pharmacological treatments. The next step is to treat them with a specific pesticide for Varroa. Several chemical treatments are available on the market, so it is essential to read up and consult an expert before purchasing or using any product. Chemical treatments should be applied according to the manufacturer’s instructions and repeated to reach a consistent reduction of the number of varroa until reaching a safety level which varies depending on the period of the year. Furthermore, as we have seen previously, it is always better to rotate the various treatments during the year to avoid the onset of resistance to anti-parasitic drugs.
3. Natural treatments. As an alternative to treatments with synthetic drugs, there are also natural remedies, among which it is worth mentioning oxalic acid. This entirely natural substance is also compatible with organic production. On the web, there is also a variety of “ambiguous” and unverified information on the use of other remedies such as dried garlic powder or the use of rosemary essential oils or many others. Always pay attention to this kind of news because, in most cases, it is unverified or incorrect information that could even cause significant damage to your bees.

(source: https://extension.psu.edu/)

Conclusions

Beekeeping for honey production is one of the oldest agricultural activities in the world, and unfortunately, it is subject to dangers and attacks by parasites such as Varroa destructor. Varroa is a significant bee parasite that can seriously harm honey bee hives. Varroa feeds on the fat body, hemolymph, and other secretions of bee larvae and adult individuals, causing various health problems. In addition, Varroa can quickly spread diseases to bees, including the so-called “deformed wings” virus (DWV), which is particularly lethal to honey bee colonies. (source: https://www.ncbi.nlm.nih.gov/)

Varroa is a dangerous parasite for bees and, if left unchecked, can destroy an entire apiary. Fortunately, beekeepers aware of Varroa’s presence in their hives can take the necessary steps to combat it, such as treatment with oxalic acid vapors, which reduce infestation and the possibility of colony death.