As the beekeeping season progresses, the Atlantic Tech Transfer Team for Apiculture has been continuing to survey regional varroa mite levels. Our team has now completed the second trial of the season which assesses mite levels mid-season following wild blueberry pollination. Continue reading this week’s blog to learn more about mid-season trends in varroa mite populations across our Maritime region, and for insight to how this year’s mite levels compare to 2024.
Mid-Season Varroa Mite Trends in the Maritime Region
For the second season, ATTTA is conducting a regional varroa
mite survey to assess temporal trends in mite levels and to assess the efficacy
of amitraz (active ingredient in Apivar® - a synthetic miticide). The second
trial of the survey consisted of 23 beekeepers (9 in Nova Scotia, 7 in New
Brunswick and 7 on Prince Edward Island). Our team aims to include as many
commercial beekeepers representing the 3 Maritime provinces as possible, and we
often reach out to more beekeepers than reflected by those who are able to
participate. The second trial took place between July 3 and August 6, 2025 following
wild blueberry pollinations, and consisted samples from 76 colonies. These
colonies are all from commercial beekeepers who provide pollination services.
Overall, the average mite load for trial 2 was 0.16%
infestation rate per sample, 76% of samples had 0 mites, and 5% of samples had
a mite load greater than 1% (Figure 1). The average number of bees per sample
for trial 2 is 291, with a target sample size of 300. In comparison, in 2024,
the average mite load per sample for trial 2 (July 3, 2024 – August 22, 2024)
was 0.3%, 73% of samples had 0% mite load, and 7% samples had a mite load
greater than 1% (Figure 1). More data is needed to help establish a baseline
for mite levels mid-season across our region. Although there is a decrease in
the percentage of colonies with detectable varroa, and the percentage of
colonies with mites levels above 1%, between 2024 and 2025 (Figure 1),
additional data is needed to support a downward trend, or assess if levels are
potentially increasing or remaining stable from year to year. The slight difference
across beekeeping seasons, as determined from the survey over the past 2 years,
may reflect the normal range of mite levels across our region, and a main
priority of the survey is to establish a baseline of the region’s mite levels.
It is important to understand that the population of varroa
mites increases throughout the beekeeping season, which is reflected by the
increase in mites sampled between May/June (trial 1) and July/August (trial 2).
The results of this survey support the fact that the population of mites
increases as the beekeeping season progresses (Figure 1). This makes early
spring monitoring and treatment for varroa mites crucial, because the
population can quickly get beyond the economic threshold if waiting until the fall
to treat colonies again.
Beekeepers need to be vigilant with monitoring for mites
each month to ensure that colonies will be strong and healthy by the time
winter preparations occur as varroa mites continue to be a top reason for
colony winter loss. If a beekeeper is seeing mites during the early part of the
beekeeping season, then they should be prepared to provide treatment by fall.
There is also the potential that the number of mites will exceed the economic
threshold prior to the fall if colonies are not treated in the spring, in which
case a mid-season knock down treatment may be indicated to keep the mite
population under control until fall treatments can occur. Through a range of
management practices, beekeepers should manage their mite levels to be below 1%
all throughout the beekeeping season, and intervene with treatment when levels
reach or surpass 1% (1 mite per 100 bees). Beekeepers should also start late-summer/early-fall
mite treatments as soon as possible when levels are at or exceeding 1% to help
ensure healthy winter bees with low virus loads.
It is important that beekeepers understand that 0% mite
load, as determined by an alcohol wash, does not mean that no mites are present
within the colony. There is always a background population of varroa mites
within a single colony and, without frequent and representative monitoring, undetected
population increases will quickly increase to beyond treatment thresholds.
Beekeepers must remain vigilant when monitoring for mites,
and practice integrated pest management in all aspects of their mite
management. There was good opportunity for growing bee populations this
beekeeping season, which also provided the opportunity for mite populations to
increase. Late summer to early fall will be a crucial time frame for monitoring
mite levels and starting any required treatments as soon as possible. For
questions regarding mite management and treatment please reach out to the ATTTA
team. We would like to thank all beekeepers who participated in trial 2 of our
survey. We will be reporting on the complete survey following trial 3 which
will take place in September.
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 attta@perennia.ca