Varroa key data:
The Varroa destructor, usually called the Varroa mite, was originally widespread in East Asia. In the bee species that live there, only the drone larvae are attacked by this parasite. Adult bees can remove the parasites there, probably due to coevolution. While the mite managed to expand its range around the world by 1980, it also came across our western honey bee, Apis mellifera. However, this does not show the pronounced natural cleaning behavior as its relatives, the eastern honeybees. This allows the animal, which is 1.1 mm long and 1.6 mm wide, to remain on the adult bees. Once it has attached itself to a western honey bee with its suction feet, it feeds on the bee's hemolymph, the liquid that transports oxygen through the body of insects. This weakens the bee enormously.
-Where are most of the mites?
In western honey bees, the drone larvae are infested with the Varroa mite up to eight times more often than the larvae of the worker bees. In the adult state, however, the mites sit more on the nurse bees that they carry to the brood.
-Why is the varroa mite particularly dangerous for the western honey bee?
The varroa mite's firm back shield protects it from being wiped off by the western honey bee. The eastern honey bee, on the other hand, has the ability to clean them off.
-Is varroosis contagious?
Varroosis not only affects your own people. If the bees are weakened too much by the Varroa mite, the surrounding colonies begin to rob their own colonies. They carry many mites into their own hive. If the beekeeper has already treated and does not check for a renewed increase in the varroa mite population in time, this previously strong predator colony now very quickly becomes very weak, which in turn attracts new strong predator colonies. If the beekeeper is not careful, all colonies in one location will quickly become so weakened that they cannot survive the winter. It is therefore all the more important to regularly check the extent of the varroa infestation after treatment against the varroa mite.
-Where does the varroa mite live?
The varroa mite spends its entire life parasitically in the beehive or on the bees. As a result, it can only get into a colony that has not yet been infected through physical contact with alien bees or through robbery.
-The females of the varro mite feed on the bees' hemolymph, the liquid that transports oxygen through the body in insects.
-While its host, the worker bee, covers the brood cell of an old larva that is ready to pupate, the Varroa mite climbs into the brood cell.
-After about 50 hours, she lays her first egg in the cell. This is unfertilized, which is why, like the bee, only one male can hatch from the egg.
-If it is now in the cell of a worker larva, it will lay another five eggs in the cell after another 30 hours. If it is in the cell of a drone larva, there are another six eggs. These are fertilized, which is why female mites arise from them.
-As soon as the mites hatch, they suck on the bee larva, like their mother before, and drink their hemolymph.
-Already in the cell the siblings mate with each other several times.
-When the bee hatches after approx. 12 days, only the older females leave the cell together with the bee. They can move around freely in the beehive and look for their new host. The males and younger female stages that did not manage to fully develop during the time limited by the capping period remain in the brood cell and die.
Consequences for infected colonies:
Bees that are infected by the varroa mite are weakened by it and are therefore more susceptible to disease. At the same time, the mites can transmit bacteria and viruses to the bees while they are suckling. So the mites act as a vector for this. This is an additional burden. Bees weakened in this way are less able to learn than healthy bees and therefore find it more difficult to return to the beehive. In addition, they usually have a shortened life span.
Bees that the mites have sucked on during their maggot stage also show more malformations such as wing deformations or a shortened abdomen.
The more bees are weakened by the Varroa mite, the greater the risk that the colony will not survive the winter.
Because of this, the mite is the main cause of bee deaths.
If a beekeeper escapes a swarm, it is assumed that it will perish from the varroa mites after three years at the latest without treatment.
Impact of the mite on infested bee colonies at a glance:
- weakened and disease-prone bee
- increased risk of virus and bacteria transmission
-Bes find it harder to get back to the beehive
-Bee has a shorter lifespan
- increased deformities
- increased risk that the people will not survive the winter
There are various diagnostic methods that can be used to determine the extent of varroa infestation.
1. The garbage diagnosis
The best known is probably the garbage diagnosis. Here, a Varroa diaper, also known as a garbage insert or floor scraper, is pushed under the colony for a few days. Then the natural varroa fall per day is calculated. This value should not exceed 5 mites / day in summer and 0.5 mites / day in winter. If these limits are exceeded, it is recommended to treat the colony against the mite promptly.
To avoid adulteration by ants and other insects that remove the mites, it is often recommended to put kitchen towels soaked in cooking oil on the Varroa diaper.
This type of diagnosis can be used all year round. It is best to check at least once a month and, if the infestation is too severe, treat the colony. Especially at the end of winter it is important to get an overview. After all, every winter mite can produce 50 new ones over the course of the next season. However, in winter it is important to watch out for the death of bees. If too many bees block the grid of the soil, mites can no longer fall through and the result is falsified.
2. Open your eyes!
The mites can be seen with the naked eye. If more mites are seen on the bees during the colony inspection, the Varroa mites should be treated urgently.
3. Icing sugar
Another method of counting Varroa mites is dusting with powdered sugar. It is mainly used between mid-July and early September.
A shaker beaker is made for this purpose: In a container with a lid with a volume of at least 750ml (e.g. a large yoghurt pot), a close-meshed grid through which the mites can fall, but which is impenetrable to the bees, is inserted or glued into the lid. You also need:
dry powdered sugar
a kitchen scale
a small, fine sieve
the lightest possible container
a sturdy piece of foil (e.g. a cover foil or a large plastic box) and
It should be noted that all materials as well as the bees are dry. Therefore, this method only works reliably in dry weather.
First, remove a few bees from the beehive. It is best to use frames that are as far away from the brood nest as possible. These are knocked off on the foil or in the large plastic box. Simply hit the hand that is holding the frame with your hand. As a result of the resulting jolt, all the bees fall onto the foil or into the plastic box. Please do not try to sweep the bees away. Too many bees get into the air when sweeping and it takes too long to collect enough bees.
Carefully fold up two opposite sides of the foil or carefully open one corner of the box with the bees so that the bees all fall into one corner. Now pour about 50g of bees into the shaker. By carefully tapping the bottom of the shaker cup on the floor, all the bees fall down and the shaker cup can be closed without pinching a bee.
Now put about three heaping tablespoons of powdered sugar in the sieve and sieve it through the grid into the shaking container. Wait about three minutes until all the bees have calmed down and have distributed the powdered sugar a little in the shaker. Then turn the shaker and pour all of the powdered sugar through the grid into the light-colored container. Carefully move the shaker up and down so that the powdered sugar can remove all the mites sitting on the bees.
You can now simply tip the bees back into the beehive, where other bees will clean them up.
Since the mites in the powdered sugar are difficult to see, a little water is put into the light-colored container in which we poured the powdered sugar so that the powdered sugar dissolves. The dark mites now stand out wonderfully from the light background and you can count them:
If more than 5 mites fall in July, 10 mites in August or 15 mites in September, the colonies should be treated.
This method seems quite brutal to some. Most of all, many do not like the shaking of the bees. Although it rarely harms the bees and it is a fairly safe method to determine the exact degree of infestation, methods such as the floor scraper with cloths drizzled with oil are much more bee-friendly. This method should therefore only be used if methods such as litter diagnosis are too uncertain, for example if too many ants remove the mites or you cannot wait a few days until all the mites have fallen.
4. Further indications that may indicate an excessive varroa infestation are:
-The people suddenly become very weak in autumn.
At the latest when the first winter bees hatch, the ratio of varroa mites to bees increases. Fewer and fewer bees live in the hive, while more and more varroa mites can still hatch. This increase in the number of Varroa mites per bee weakens the colony enormously. They are more prone to predation and less able to withstand wasp attacks. The people become weaker very quickly within a very short time until they finally die completely.
-If the varro pressure increases, the number of malformed bees also increases. For example, they have a deformed abdomen or deformed wings.
Varroosis in other countries - a notifiable or notifiable disease?
In Germany, varroosis is neither notifiable nor notifiable. According to the responsible authorities, the degree of infestation is too high for it to be worthwhile to evaluate the number of colonies affected.
In Switzerland it looks different. Here, varroosis is regarded as an “epidemic to be monitored”. It is also notifiable.
Austria has by far the hardest classification of varroosis compared to its neighboring countries. Here, varroosis is considered an animal disease and is therefore not only notifiable, but also notifiable.
Comparison of different treatment methods
Hyperthermia is therefore definitely a method that can assert itself against conventional chemical and biological methods. More information can be found here: