The varroa mite is largely responsible for bee deaths. We show what helps against the Varoa mite and how you can fight it.
The Varroa mite is at the top of the list of pests that can occur in a bee colony. Modern beekeeping has had to adapt to this for a long time and should be on guard against this annoying mite around the clock.
Varroa mite: origin and profile
When a beekeeper is dealing with pests in their hive, at the top of any pest list will be the varroa mite (Varroa destructor). This mite finally managed to spread from Asia all over the world and since 1980 at the latest every beekeeper has been confronted with the varroa mite. The mites live in all their life stages as a parasite on the honey bees or in the hive. The adult mites are 1.1mm long and around 1.6mm wide, with males being smaller than females - however, up to 80 percent of Varroa mites are females.
These mites attach themselves to the bees and feed on the bees' hemolymph. The hemolymph is the body fluid of insects that transports oxygen through the body - comparable to the blood in humans. When the varroa mites attach themselves to the forager bees, they are conveniently transported from one place to the next. The smell of the drone larvae (male bees) is particularly attractive to the mites. When the mites lodge in the brood cells, they feed on the larvae, causing these infested bees to become deformed.
The Varroa mites reproduce incredibly quickly and then lay their eggs in the cells. This rapid multiplication of the pests creates ever greater unrest in the beehive and the bees become more susceptible to disease. In the worst case, the entire colony could collapse within two years.
When a female latches on to a beesucked, then it leaves the worker bee while it is capping a brood cell and climbs into this cell. There the mite now sucks on the bee larva and lays its first egg after about 50 hours. The mite lays more eggs at intervals of 30 hours - a female produces a total of five or six eggs. When mites hatch from these eggs, they also feed on the bee larva, mate in the cell and the females leave the comb as soon as the bee hatches - this happens after about 12 days.
Why is the Varroa mite so dangerous?
The varroa mite is now considered the most important bee pest. In Germany, varoosis (the infestation of a beehive with varroa mites) does not have to be reported, but this is not the case everywhere. In Switzerland, varoosis is considered a "disease to be monitored" and there is an obligation to report it. In Austria, varoosis is notifiable as an animal disease.
These legal regulations already show the importance of the Varroa mite for beekeeping. The varroa mite weakens the bees through their sucking activity, which reduces their ability to learn. Due to the weakening, they often cannot find their way back into the hive.
In addition to weakening, the mites also transmit viruses to the bee. The Varroa mite thus weakens the immune system of the bees, and they also become more susceptible to viruses and other pathogens. Bee deaths in autumn and winter are largely caused by this noxious mite.
Detect Varroa mites
You can tell whether your beehive is infested with Varroa mites by the following typical symptoms:
- Your colony suddenly dies in autumn
- Small red-brown dots can be seen on the bee larvae
- Newly hatched bees have deformities such as a deformed abdomen or deformed wings
- A massive infestation is shown by mites on the backs of adult bees
You can use the following methods to check whether your hive is infested with Varroa mites. You should use these methods and techniques regularly and not just when you suspect that your bees are already suffering from a Varroa infestation - precaution pays off here.
The following variants belong to these control methods, which we would like to briefly present to you in detail:
- Investigate Drone Spawn
- Icing Method
- Open underbody
- Watching bees
1. Investigate Drone Spawn
As the varroa mites are particularly attracted to the drone brood, you can check these larvae for an infestation. First you need to find a frame with capped drone brood. This is easy to spot as drone brood is very convex and larger than worker brood. The diameter of a drone brood is about 8 mm, the diameter of a worker bee is about 6 mm. Remove the frame from the hive, shake off any bees and move the frame to a quiet workspace.
Unfortunately, this method will kill some of your larvae. It is best to put the frame in the freezer. Next, uncap the cells containing the drone brood with an uncapping knife. Impale the cell lid with the doll.
Next, pull the drone pupa out of the cell and check for a Varroa mite infestation. The dark mites are easy to spot on the light-colored pupae. Repeat this a few times and if you find more than two mites on a pupa, you already know you have a serious infestation. If you find 2-3 mites on 50 pupae, it means you have a moderate infestation.
2. Icing MethodAnother method of checking for a Varroa infestation is the powdered sugar method. To do this, take an empty screw-top jar, make a hole in the lid and insert a narrow insect screen there. Remove 200 to 300 bees from the brood box and place them in the jar - but do not remove the queen.
Now put three to four spoonfuls of icing sugar in the jar and close it. Hold the lid with your hand and shake the jar vigorously for 30 to 60 seconds. By holding it closed, no sugar can escape. You do not have to worry about your bees, they will not be harmed. In any case, you should shake really vigorously so that the mites detach from the bees.
After shaking, place the jar in the sun to let the mites fall off. Then shake vigorously again as before, turn the glass upside down and let the sugar trickle onto a white piece of paper.
After about 15 minutes you can open the jar and the bees near thedrop off the entry hole. Because of the sugar, the bees can't fly yet, but their fellow bees are happy to clean them. Note that the bees will not be in the best of moods after the shake, so don't get too close to them.
Pour the rest of the sugar from the glass onto the paper. You can now easily recognize the mites there. If you find more than 12 mites, it is already an advanced infestation.
3. Open underbody
This method is fine for routine checks, but it's not as reliable as the previous two. About 10 percent of Varroa mites detach themselves from the bees and then fall to the bottom of the hive. There the mites are now waiting for the next bee that they can infest. But now you can use an open subfloor with a Varroa drawer. Inside is a sticky layer of cardboard (diaper) to which the mites then stick. You can also coat this surface with petroleum jelly or cooking oil to increase stickiness.
Pull out that sticky cardboard layer at least once a day and count the mites on it. For example, if you find five to ten mites a day in July, you should start treating the pests immediately. In the months of October and November, an average of no more than 0.5 mites per day may fall off.
Clean this surface after each count and see if ants may have removed mites from the drawer. After cleaning, brush the surface again with a little oil so that the mites stick again.
4. Observe beesThere is also an interesting observation that can be made to identify a Varroa infestation. This includes observing the bees in front of the flight front in the grass. If young bees wander around in the grass in front of the hive, one can assume that these bees have been rejected by the colony. The higher the Varroa pressure is, the more bees you will find in the meadow - these bees can then also be examined for any deformities.
Fighting varroa mites: remedies and methods against the bee enemy
If you have found an infestation with Varroa mites, it's time to fight it. Fortunately, there are many different methods that can be used against these mites, which we are happy to share with you.
Grid shelfattach
This is a very simple but effective method. For this purpose, a metal grid with a hole size of two to three millimeters is used as the bottom of the hive. Underneath is a bowl, also known as a Varroa trap. The mites fall through this grid and are then trapped in this bowl. This measure slows down the development of Varroa mites and slows down the infestation.
The Vaseline Method
In this method, you simply put some petroleum jelly in the bees' brood chamber. And that's all the beekeeper has to do. The bees will walk over the petroleum jelly over time and then have marks of the same on their legs. When the bees then clean themselves, the Vaseline gets to the mites and different things can then happen. Either the mite can no longer hold on to the bee's body and falls off the bee, or the Vaseline blocks the mites' breathing openings and the Varroa mites then suffocate.
Dusting with icing sugar
The icing sugar can not only be used to identify the varroa mite, but is also suitable for combating it. To do this, the icing sugar is simply sieved several times so that it is very fine and there are no coarse particles left in it. Then you fill the fine sugar in a baby powder box or something similar and you can start with the treatment.
To do this, take each frame with the honeycomb out of the hive and dust both sides with powdered sugar. Each bee should then have a fine white veil and the sugar can unfold its effect. Because this is what happens:
- The mites lose their suction cups and fall off the bees
- The bees will start preening themselves to remove the powdered sugar. With this brushing, the mites that are still attached to the bees are removed by the bees themselves and fall off
- The sugar bothers the mites and can also block the respiratory openings. This also allows the mites to let go of bees
This treatment can be used as often as you like, but it takes a lot of effort and often disturbs the bee colony. To get the best results from this method, you would need to do the powdered sugar method three to four times about a week apart. This would then also capture the newly hatched mites.
Remove Drone Spawn
As mentioned before, the drone brood is particularly interesting for the mites. Therefore, this is removed from the hive and with it many Varroa mites. This removal can delay mite growth.
Apply formic acid and oxalic acid
The organic acids formic acid and oxalic acid are very popular as agents against the Varroa mite. Bees tolerate these acids well in low concentrations, but they can also be harmed by this treatment.
These treatments should be carried out after the honey harvest at the end of July. The acids can be introduced into the beehive in a variety of ways. The advantage of these acids is that they also act on the capped brood and reduce all stages of the mites. On the one hand you can use the sponge cloth method or the Nassenheider evaporator. With both methods, the acid is evaporated so that it spreads throughout the hive. These methods are also permitted for beekeepers who produce organically and promise the greatest success.
Chemical methods to combat the Varroa mite
Meanwhile, researchers at the University of Hohenheim have succeeded in finding a drug against the varroa mite that can be given to the bees when they are fed. We are talking about lithium chloride, which is also used in human medicine as an antidepressant. This s alt can be dissolved in sugar water for the bees to feed, and the varroa mites that try to suckle on the bees should die off within a few days.
The remedy hasn't shown any side effects on the bees yet and some testing needs to be done before it can be put on the market. In any case, it promises hope in the fight against the small pests.
There are also already studies on resistance breeding of bees against Varroa mites. However, these investigations are still in their infancy.
In this article you will find out how you can support your bees in the garden and lots more information about the little buzzards.