by Véto-pharma Beekeeping involves carefully managing bee colonies to ensure their health while combating pests and diseases that endanger their survival. A major concern for beekeepers globally is effectively controlling Varroa destructor mites. These mites are well-known for their role in weakening bee colonies, spreading viruses, and contributing to colony collapse [1].
Over the years, various treatment methods have been developed to control Varroa mites, including chemical treatments such as amitraz and organic/natural treatments like oxalic acid. However, the combination of these treatments requires careful consideration due to potential interactions that can affect their efficacy. Additionally, ongoing research explores combining treatments to improve Integrated Pest Management (IPM) strategies [2].
Amitraz is a widely used pesticide in the beekeeping industry, known for its effectiveness in controlling Varroa mites [3-4]. It works by interfering with the nervous system of the mites, leading to their paralysis and eventual death. Amitraz is typically administered using strips placed inside the hive, where they slowly release the active ingredient over a period of weeks.
This slow-release mechanism ensures prolonged exposure to the mites, thereby enhancing the treatment’s effectiveness. However, like all chemical treatments, the efficacy of amitraz can be influenced by various factors, including environmental conditions and interactions with other actives [5]. One such interaction is with oxalic acid, a treatment that has gained popularity due to its organic nature and effectiveness in mite control.
Oxalic acid is a naturally occurring organic compound that is used in beekeeping as a miticide. It can be administered in several ways (vaporization, spraying or dribbling), but vaporization is one of the most common used methods, especially among commercial beekeepers. During vaporization, oxalic acid is heated and the vapor is then introduced into the hive. The vapor settles on the bees and hive surfaces, effectively killing the Varroa mites.
One of the key benefits of oxalic acid is that it leaves no harmful residues in the hive, making it a preferred choice for organic/natural beekeepers, although at high and sub-lethal doses, it can be harmful to the bees [6-7].
However, the process of vaporization creates a highly acidic environment, which can interact with other treatments, such as amitraz strips.
Some beekeepers, facing difficulties in managing infestations, reported having successively applied a treatment based on oxalic acid followed by amitraz strips within a short period of time. Despite these interventions, the number of varroa mites remained surprisingly high. This phenomenon can occur, for example, at the end of the season when it may be tempting to use a quick treatment to ‘knock down varroa mites’ just before applying the strips. One might also question the impact of multiple oxalic acid vaporizations during the season on the effectiveness of the end-of-season amitraz treatment.
This observation suggests that the acidic environment created by oxalic acid could degrade amitraz, thereby reducing the effectiveness of the treatment. However, controlled field trials are necessary to confirm and better understand this hypothesis.
Similarly, we can consider the same hypothesis for the consecutive application of formic acid followed by amitraz, although this combination is somewhat less common than using oxalic acid with amitraz.
Conversely, there are anecdotal reports from beekeepers who have achieved effective mite control by spacing out the treatments—applying amitraz strips during the brood-rearing season and reserving oxalic acid vaporization or dribbling for the broodless period in late fall. This approach, which avoids the simultaneous use of both treatments, appears to have resulted in significant mite reduction and healthier colonies.
Considering the potential for reduced efficacy when combining amitraz strips and oxalic acid vaporization, beekeepers need to carefully plan their treatment strategies to avoid negative interactions. Here are some key considerations for effective Varroa mite control:
Combining treatments has been proposed as a promising approach to improve Varroa IPM strategies [10]. This idea has precedent, as combinations involving amitraz have been tested against other arachnids, such as the tick Rhipicephalus microplus [11]. Using a combination of registered products could potentially achieve rapid and effective Varroa control.
However, only a few researchers have explored combinations of chemical varroacides (e.g., Toomemaa 2019, Pietropaoli and Formato 2022 [12-13]). In 2024, Aurell et al. tested a combination of Apivar (amitraz 3.3%) [14] and Apiguard (thymol 25%). Previous studies indicated no synergistic toxicity to adult honey bees between thymol and amitraz [15]. Since Apivar® is highly effective when brood is present [16], it served as the cornerstone of their combination strategy. The study incorporated Apiguard® because it can be used in temperatures up to 40.6°C (105°F) [17], remains effective even with brood present [18], and has no reported cases of Varroa resistance to thymol [10].
However, these combinations should not currently be used in the field as they require careful testing in a research program and need to be tailored to the specific conditions and needs of each apiary. Further research will be necessary to assess the efficacy and safety of these combinations, as well as to determine the best application methods and dosages. Additionally, validation by the authorities is required to evaluate the benefit/risk ratio.
Effective Varroa mite control demands a detailed understanding of the interactions between various treatment methods. While amitraz strips and oxalic acid are both valuable tools in the beekeeper’s arsenal, their combination can lead to reduced efficacy due to the rapid degradation of amitraz in acidic environments.
By strategically planning treatments, monitoring mite levels, and adopting an integrated pest management approach, beekeepers can achieve better outcomes and ensure the health and vitality of their colonies.
by Véto-pharma The contents of this page are intended for the American public. The instructions for use of the miticites mentioned comply with US regulations. Table of contents In the context of
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