What are Varroa Mites?
Recent research has revealed new insights into the impact of Varroa mites on honey bee colonies. Contrary to previous assumptions, it has been discovered that Varroa mites feed on the fat body of honey bees rather than their haemolymph. This feeding weakens the bees and ultimately leads to their death. Parasitized bees have lower body mass and reduced nutritional reserves, compromising their immune defenses.
When the mites feed on the bees, they create wounds in the cuticle and keep them open with their lateral lips, allowing various viruses and pathogens to invade the bees’ bodies. This results in a complex disease known as Varroosis. The presence of Varroa mites significantly shortens the lifespan of infested honey bees, posing a significant challenge for winter bees that need to survive until spring when honey bee populations typically increase.
Studies have demonstrated a correlation between higher levels of Varroa mite infestation and increased winter colony losses. In fact, winter losses are more likely when there is a natural mite fall of 3 mites per day in December, and the risks escalate with higher infestation levels.
Varroa destructor, the acarid mite responsible for this threat, is widespread in honey bee colonies worldwide. It poses a substantial risk to honey bee health, necessitating effective strategies to manage and control Varroa mite infestations.
The Lifecycle of a Varroa Mite
Varroa mites reproduce within honey bee brood cells during the capped phase, which typically lasts for 12 to 14 days. Female Varroa mites penetrate the brood cell just before it is capped, allowing them to carry out multiple reproductive cycles. The duration of the phoretic phase, during which mites are on adult bees rather than within capped cells, can vary. After maturing in phoresy for approximately seven days, an impregnated young female mite can infest a cell and start its first reproductive cycle. Subsequently, the length of the phoretic phase depends on the availability of suitable cells for infestation.
The lifespan of Varroa mites is adapted to the life cycle of bees. In the summer, females can live for one to two months, while in the winter, their lifespan extends to six to eight months in the absence of brood. Only impregnated female mites, known as foundress mites, can parasitize adult bees and survive outside of brood cells. Males and non-impregnated females do not survive after the emergence of young adult bees and are discarded by worker bees.
Infestation levels are typically higher in male brood cells compared to worker brood cells during the beekeeping season. The impact and level of infestation may be less noticeable, except when male brood is reduced, leading to a mass transfer of Varroa mites to worker brood. The spread of Varroa mites from one hive to another, often through robbing weakened colonies or drifting of bees, plays a significant role in the dynamics of Varroa populations.
Swarming temporarily interrupts the population explosion of Varroa mites. During the broodless period of approximately three weeks when new queens emerge and part of the phoretic Varroa population leaves with the swarm, there is a momentary reduction of around 15 to 20 percent in the Varroa population within the original colony.
How to Check for Varroa Mites?
To ensure the health and survival of bee colonies, regular monitoring for mite infestations is crucial. Ideally, monitoring should be conducted at least three times a year, with a recommended fourth check for broodless colonies. These monitoring intervals include early spring, after the honey flow, and following the late summer treatment in fall. Additionally, a final assessment in November before overwintering can provide valuable insights.
Accurately assessing and understanding mite populations is the foundation of an Integrated Pest Management (IPM) control strategy. Delaying the confirmation of elevated mite numbers poses risks to colony survival. Waiting too long to address infestations can jeopardize a colony’s chances of making it through the winter and contribute to mite transmission among other colonies.
Soap or Alcohol Wash
Among the various methods available for assessing mite infestations, the alcohol wash method stands out as the most accurate, reliable, and economical option for beekeepers. Widely practiced by beekeepers, apiary inspectors, and scientists across North America, this method provides consistent and precise results.
To conduct the alcohol wash method, begin by preparing a honey jar filled halfway with rubbing alcohol (or winter windshield washer fluid). Collect approximately half a cup of bees, totaling around 300 bees, from one or more brood frames. It is essential to ensure that the queen is not included in the sample, as this method unfortunately results in the mortality of the bees.
Gently place the collected bees into the jar containing the alcohol. Carefully swirl the jar for about a minute to detach the phoretic mites from the bees. For those employing devices like the Varroa EasyCheck, which incorporates a filtering screen, mite counting can be performed directly. If such a device is unavailable, strain the contents of the jar through a fine sieve, with a mesh size of eight openings per inch, to separate the bees from the liquid. This process allows the liquid and fallen mites to flow through while retaining the bees. Count the mites present in the strained liquid.
To maximize the utility of the alcohol wash method, the liquid can be reused multiple times. After mite counting, filter the liquid through a very fine screen to remove any residual mites, ensuring a clean solution for future assessments.
In conclusion, the combined use of the Varroa EasyCheck device and the alcohol or soap wash methods provides beekeepers with effective means of testing for varroa mite infestations in their bee colonies. These tools offer accurate and reliable results, allowing beekeepers to assess the mite population levels and take appropriate action. To acquire the Varroa EasyCheck device, beekeepers can conveniently purchase it from Dadant & Sons, a trusted source for beekeeping supplies. By incorporating these testing methods into their regular monitoring routines, beekeepers can proactively manage varroa mite infestations, safeguard the health of their colonies, and promote the long-term sustainability of their beekeeping operations.