Autumn-Winter Anti-Varroa Treatments

In the colder season, the queen stops oviposition and, at the same time, the development cycle of the varroa also comes to a halt, which goes hand in hand with the development of the bees' brood. The varroa, therefore, is in the foretic phase and is therefore particularly susceptible to the action of acaricides. This is why effective action at this time of year is essential in order to have colonies with a low infestation rate in spring that can resume their growth process without problems. What are, however, the most commonly used types of treatment?

One of the most popular methods is the use of oxalic acid, also because it is allowed in organic. For it to be effective, it must be carried out in the absence of brood as it cannot act on varroa protected by the wax operculum of the brood cells. The beekeeper, depending on time and availability, may opt for drip or sublimate administration. Both must be carried out at temperatures that are not too cold. Depending on the type of product used, general indications suggest administering it at temperatures around 10°C or higher.

Oxalic acid drip is certainly the simplest and most affordable method, but it presents some problems. Firstly, it must be performed in the total absence of brood in order to be effective. This means that a careful inspection must be carried out before administration and, if necessary, the little brood that can be found must be removed. In addition, the drip can only be carried out once and, therefore, the timing must be strictly adhered to. The best known and most widely used product is certainly API-Bioxal. To administer the drip, a sugar solution must be prepared in which the oxalic dihydrate is dissolved. The 1:1 syrup should be prepared by dissolving the sugar in distilled water brought to 50°C. Another oxalic acid product that can be administered either as a drip or as a spray is OXUVAR 5.7%.

Since the administration of drip is strictly linked to weather conditions and the timing with which it is carried out, many beekeepers prefer to opt for sublimation. This is certainly more expensive, given the need to purchase the specific equipment and the protective gear that the beekeeper must wear. However, it has many positive sides, including the possibility of repeating it over time until an even level of cleanliness is achieved in the apiary. Should presence of brood be detected, one can proceed in several ways. If the brood is not very extensive, it can be eliminated (by straining it or removing the honeycomb) and then treatment can be carried out, duly repeated after 7-10 days. If, on the other hand, the brood is more developed, 3 successive treatments of sublimate can be carried out, again 7-10 days apart. Repeat the treatment 3 times.

For the sublimate, it is necessary to purchase a appropriate sublimator, equipped with an electrical heating element. After pouring the oxalic on the switched-off device, it must be introduced through the front opening of the hive, taking care not to touch the combs. Subsequently, all outlets must be closed to prevent the dispersion of fumes. The device must be operated for 3 minutes and the flight opening can be restored no earlier than 10 minutes after the end of the treatment. After finishing treatment, the sublimator can be cooled and cleaned with plain drinking water.

The other route one can take, if one does not want to use oxalic or if one is not organic, is to resort to synthetic acaricides. The most commonly used ones are Amitraz-based and are Apivar and Apitraz. Even in this case, however, use in the absence of brood is more effective. According to the indications provided by the IZS delle Venezie, Apivar should be used at the end of summer, placing the two strips of product in the hive for 42 days and then removing them. Apivar is also used in the later autumn, keeping it inside the hive for a longer period and if necessary moving the strips by following the movements of the glomerulus. This is done by hanging two strips of Apitraz from two combs of stock, where there is more bee passage, and then removing them after 6 weeks.

Finally, another product is also indicated, Varromed, composed of both oxalic and formic acid. For this reason, it is also considered effective in the presence of brood. The dosage of the product is closely linked to the number of bees present in the hive. This treatment may require several applications, to be carried out at 6-day intervals, depending on the different varroa fall at the bottom. The product must be administered in the late afternoon-evening, when the bees decrease their flight activity. Before distribution, it is important to heat it to 25-35° and then shake it well.

It can happen, however, that in areas with a particularly mild climate, a natural brood freeze does not occur. So what can be done in such cases? Obviously, one must proceed as one does in summer, i.e. by adopting biotechniques that lead to an artificial blockage of the brood. This can be done by either confining the queen in a cage (like a Chinese cage) or by isolating the entire honeycomb on which the queen is present, and then releasing her after about 21 days when all the pupae have hatched. At that time, oxalic drip is administered and then, after a few days, the treatment can be repeated with sublimate. If the brood is not particularly large, one can also opt for the total removal of the brood and subsequent treatment with oxalic.

It is very important to follow the instructions for correct administration of treatments. Wrong dosage or incorrect administration may bring more harm than good, such as the death of the bees themselves or total ineffectiveness of the treatment with re-infestation of neighbouring apiaries. It is good practice to treat the same apiary, which generally has a homogeneous infestation rate, at the same time. Last but not least, one must choose the right timing for administration. Not only must the weather conditions be favourable, but it must be ensured that the brood is totally absent or, at least, as small as possible. Visual inspection is not always possible, which is why the use of remote monitoring tools of the hives can be a trump card.