Beekeepers in Atlantic Canada are all too familiar with
managing a variety of honey bee pests and diseases. Fortunately, they have a
wide variety of tools available to ensure the health of their colonies. Using a
variety of strategies to manage pests, including chemical, biological,
cultural, and physical controls, as well as limiting the frequency of chemical
treatments, is part of integrated pest management (IPM). Integrated pest
management is the best management practice for beekeepers, as it aids in
preventing an overreliance, and potential reduced efficacy, of chemical
treatments. A key component to any beekeeper’s IPM plan is monitoring the
population levels of pests and diseases. This week’s blog will discuss Varroa
mite monitoring options, the advantages and disadvantages of each, and the
overall importance of assessing pest population levels before and after any
treatment.
An IPM Series: The Importance of Monitoring for Pests and
Diseases
In Atlantic Canada, the pest most monitored for is Varroa
destructor. Varroa are parasitic mites of honey bees that cause severe
damage to colonies if left untreated. They cause damage through direct feeding
on bees, and by the transmission of a variety of viruses. That is why it is
important to monitor Varroa mites and treat against the pest when population
levels reach the economic threshold. There are a variety of ways to sample
colonies, both to determine if mites are present at levels that are damaging to
the colony, and to assess the effectiveness of control measures.
Washing samples of adult bees is a common way to determine Varroa mite infestation levels. Both alcohol washes and ether rolls require a sample of 300 bees (1/2 cup) from the brood nest. These nurse bees are the most likely to have adult Varroa mites parasitizing them. However, the brood nest is also the most likely location of the queen, so it is important to either isolate her or make sure she is not on the frame being sampled. For directions on how to perform an alcohol wash or ether roll refer to ATTTA’s “Summer Disease and Pest Monitoring in Honey Bees” fact sheet. For an alcohol wash in May, the economic threshold is 2 mites per 100 bees, and in August it is 3 mites per 100 bees. For an ether roll in May, the economic threshold is 1 mite per 100 bees, and in August it is 2 mites per 100 bees. One advantage to washes is that there is a predetermined economic threshold to indicate if treatment is required. Additionally, washes only require one trip to the bee yard and results can be obtained instantly. A disadvantage of washes is that 300 or more bees are killed during the sampling. Also, when doing washes, only a small sample of the colony population is being assessed.
Sticky boards are an effective
and easy way to assess mite levels in a colony. The sticky board is placed in a
screen bottom board and after 24 hours it is removed, and the number of mites
is counted. In May the economic threshold is 9 mites per 24 hours, and in
August it is 12 mites per 24 hours. This method of monitoring also doubles as a
physical (non-chemical) treatment to reduce Varroa mite numbers. A main
advantage of sticky boards is the entire hive is the sample. Additionally,
sticky boards do not kill bees or endanger the queen. A disadvantage of sticky
boards is that they require two trips to the bee yard and potentially
additional equipment.
There are also a couple of other less common monitoring
options. The sugar shake method dislodges mites from bees. Like the washes, 1/2
a cup of bees is collected in a jar, and then the bees are coated in sugar
which dislodges the mites. Once mites have been shaken out of the jar, the sugar-coated
bees are returned to the hive. Another less common monitoring option is the CO2
method. In the CO2 method, bees and mites are anesthetized by
exposure to carbon dioxide gas. The sample of bees is then gently shaken
causing the mites to fall from the bees. The bees are then returned to the
hive. The supposed advantage of both methods is that the bees are returned to
the colony unharmed. This assumption of
bees surviving the procedure is unproven. A disadvantage of both methods is
that although it will detect the presence of mites, there is no standard
economic threshold in Atlantic Canada for these methods.
It is essential to monitor for pests and disease not only
before treating colonies, but also following treatment to know if the method of
treatment was successful. For more information about the importance and
challenges of IPM, be sure to read the next two blogs in this series.
Connecting with ATTTA Specialists
If you’d like to connect with ATTTA specialists or learn more about our program, you can:
visit our website at https://www.perennia.ca/portfolio-items/honey-bees/
Email abyers@perennia.ca