The varroa destructor is a parasitic mite that infests the Asian honey bee, Apis cerana, and also the western honey bee, Apis mellifera, which came into contact with the mite during commercial exchanges in the second half of the 20th century. Since then bees have been severely affected by the parasite, which has become one of the main causes of bee mortality in winter.
The consequences of the action of this parasite include:
- Swarm reduction
- Malformation and paralysis
- Behavioural alterations (change of queen or abandonment of the hive).
The female varroa mite acts by entering a honey bee brood and waiting for a cell, especially a kelp cell, to be hatched in order to lay its eggs, which hatch at the same time as the young bee leaves the cell. Then the mite, which comes out of the hive attached to the bee, begins to feed on the hemolymph of the adult bee and the brood, causing changes in the bee’s weight. Sick bees’ weight is lower than normal and they have a shortage of carbohydrates and proteins, as well as malformations and problems with their immune system.
The bees’ immune action is provided by their natural vaccine, vitellogenin, a glyco-lipo-protein transmitted to the developing larvae, which apart from participating in the immune system, acts as a protein reserve accumulated within the bee and is essential for the survival of the bees and brood during the winter period.
During the late summer period, the formation of the so-called winter bees begins and they are going to have a longer life cycle than the bees of the mild and warm seasons. It is precisely during this period that it is necessary to ensure, in addition to correct bee feeding, careful prevention of varroa infestation. It is precisely during this season that varroa mites develop most, and if they were to settle in the hive they would cause the birth of bees with a low body weight and a low amount of vitellogenin, resulting in bees unable to feed the younger larvae, which will grow with a shorter life expectancy and insufficient to survive the winter.
Considering the extent of the spread of varroa, the guidelines of the National Reference Centre for Beekeeping recommend at least two preventive treatments per year, one in summer and one in winter:
- The summer treatment aims to reduce infestation in order to preserve the production of winter bees, which therefore have a fairly long life cycle
- The winter treatment aims to reduce infestation at the beginning of the honey production season
There are two main types of treatment: those of natural origin, which are allowed in organic beekeeping, and those with synthetic chemical molecules. Natural medicines are based on thymol, oxalic acid and formic acid, while chemically synthesised medicines are mostly based on Amitraz and Tau-Fluvalinate.
Oxalic acid treatment has an acaricide efficacy of about 95%, is recognised for organic production and is one of the cheapest, but must be carried out during the winter period, as it should be administered in the absence of brood. In order to achieve broodlessness, it is preferable to use the brood block technique, which means confining the queen for a period of 25 days. At the end of this period the new family will be treated from the brood combs.
Independently of the nature of the treatment you decide to administer to your bees, it is essential not to fail to administer preventive care, as an untreated varroa-infested brood has a life expectancy of only a few years. Moreover, if you have several hives, it is recommended that you administer the treatment to each one of them at the same time.