What is varroasis and why is it a major problem for bees?
Varroasis is a parasitic disease caused by the Varroa destructor mite, an ectoparasite that attaches itself to adult bees and developing larvae. This parasite feeds on the bees' hemolymph, their vital fluid, weakening them and reducing their life expectancy.
The impact of varroasis on a colony can be catastrophic. Infested bees are more vulnerable to disease, including viral infections such as deformed wing virus (DWV), which prevents young bees from flying and foraging properly. Heavy infestation can lead to the death of the majority of workers and the queen, resulting in colony collapse within a few months.
The danger of varroasis also lies in its ability to spread rapidly from hive to hive. Bees visiting infested colonies, as well as the looting of weakened hives, encourage the transmission of the parasite. It is therefore essential to regularly monitor the presence of varroa mites and adopt effective management strategies to prevent the spread of this disease.
What are the signs of varroa infestation in a hive?
Varroa infestation can be detected on several levels. It's crucial for beekeepers to know how to identify the signs of infestation so they can act quickly and effectively.
Visible signs on adult bees
- Small reddish-brown dots on the abdomen or thorax of bees. These dots correspond to varroa mites feeding on the bee's body.
- Deformed or crumpled wings, a sign of the deformed wing virus, often linked to varroasis.
- Abnormal bee behavior, including loss of energy, slowed movements and difficulty flying.
Signs within the hive
- Perforated or disorganized brood, due to varroa development in capped brood cells.
- Increased adult bee mortality, with numerous dead bees at the hive entrance.
- Bees crawling on the ground, often unable to fly.
- Reduction in overall colony population, accompanied by a drop in foraging activity.
Varroa mite detection methods
Several methods can be used to measure infestation:
- Powdered sugar test: This involves taking a sample of bees, sprinkling them with powdered sugar and shaking to loosen the varroa mites, which then fall onto a white background.
- Alcohol test: A more precise but more intrusive method, where a sample of bees is immersed in alcohol to loosen and count the varroa mites present.
- Sticky plate under the mesh floor: This captures any Varroa mites that fall naturally from the hive, allowing us to assess the infestation.
Why opt for natural solutions against varroa mites?
Chemical treatments against varroa, such as amitraz, fluvalinate or coumaphos, have shown significant limitations over time.
Negative effects of chemical treatments
- Development of resistance: Repeated use of certain acaricides has encouraged the emergence of resistant varroa strains, rendering these treatments ineffective.
- Contamination of hive products: Certain chemical residues can accumulate in frame wax and contaminate honey.
- Weakening of bees: Certain treatments can alter the behavior and health of bees, diminishing their ability to orientate and forage efficiently.
Faced with these limitations, natural solutions offer a more sustainable alternative, more respectful of bees and compatible with organic beekeeping.
What are the best natural solutions for treating varroasis?
Varroa destructor can be effectively controlled by a number of natural methods.
Oxalic acid
Oxalic acid is a substance naturally present in certain plants such as rhubarb. It is commonly used in beekeeping in several forms:
- By dripping: A mixture of oxalic acid, sugar and water is applied directly to the bees.
- By sublimation: oxalic acid is heated and transformed into steam to penetrate the entire hive. This method is highly effective.
- By spraying: A solution is sprayed onto frames and bees.
Formic acid
Formic acid is another natural acaricide, particularly effective because it works even inside capped brood cells. It is generally applied using impregnated strips.
Essential oils
Certain essential oils have been shown to have acaricidal and colony-stimulating effects:
- Thymol: Extracted from thyme, it disrupts varroa respiration.
- Lavender and peppermint: have repellent properties and boost bee immunity.
Mechanical trapping and genetic selection
- Male frames: Varroa prefer to infest drone brood. A special frame can be inserted, then removed and destroyed once capped.
- Genetic selection: Some bee lines, such as the VSH (Varroa Sensitive Hygiene) bee, detect and eliminate Varroa mites naturally.
Hyperthermia
This technique involves heating hive frames to a specific temperature (around 42°C), which kills varroa mites without affecting the bees.
How to prevent varroa infestation in hives?
- Regularly monitor infestation levels with suitable tests.
- Avoid introducing infested colonies into the apiary.
- Renew wax regularly to limit parasite accumulation.
- Maintain a good balance between hives to avoid transmission of the parasite.
Varroasis control is a major challenge for beekeepers. By combining several natural solutions and carefully monitoring the evolution of the infestation, it is possible to effectively control Varroa destructor while preserving the health of bees and the quality of hive products.
