The Atlantic Tech Transfer Team for Apiculture is continuing with their second year of a regional varroa mite survey. This survey aims to determine seasonal trends in varroa mites across the region, and help assess the efficacy of mite management. This week’s blog will explore early season trends in varroa mite populations across our Maritime region, and discuss how this year’s mite levels compare to 2024, and other regions within Canada.
Early Season Regional Trends in Varroa Mite Populations
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). This year,
the survey consists of 20 beekeepers (7 in Nova Scotia, 9 in New Brunswick, and
4 on Prince Edward Island). For trial one, which took place mostly before
colonies went to wild blueberry pollination, there was a total of 71
samples/colonies included.
Overall, the average mite load for trial one (April 30, 2025 – May 28, 2025) was 0.02%, 96% of colonies had 0% mite load, and no colonies had a mite load greater than 1% (Figure 1). The average number of bees per sample for trial one is 278, with a target sample size of 300. In comparison, in 2024, the average mite load for trial one (May 16, 2024 – June 25, 2024) was 0.09%, 93% of colonies had 0% mite load, and 5% colonies had a mite load greater than 1% (Figure 1). More data is needed to help establish a baseline for mite levels in spring 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.
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 the
population can quickly increase above the level of detection. Beekeepers should
manage their mite levels to be below 1% all throughout the beekeeping season,
and intervene with treatment if levels reach/surpass 1% (1 mite per 100 bees).
A recently published study which took place in Ontario
beekeeping operations (2015-2019) demonstrated a similar seasonal pattern in
varroa mite populations, as observed from ATTTA’s research in 2024, and
preliminary data for 2025 (Sobkowich et al. 2025). This seasonal pattern
can be described by an initial spike in early spring around hive opening,
followed by a sharp decline due to initial spring treatments, succeeded by a
gradual population increase over the summer, leading to exponential growth in
the mite population in early fall. This seasonal trend is consistent with
previous knowledge on varroa mite population dynamics and global observations based
on reported mite levels to the World Organization for Animal Health (Fanelli and
Tizzani, 2020).
The Maritime industry must remain vigilant regarding the
efficacy of Apivar® (active ingredient amitraz) as this is the only recommended
synthetic miticide available, and widespread resistance is being reported
across the globe. Following severe colony losses reported in early 2025 across
the United States, researches of the United States Department of Agriculture
(USDA), analyzed honey bee samples from 6 large commercial beekeeping
operations and have submitted their results for publication. These operations
represent a collective summertime high of 183,750 managed colonies, which is roughly
6.8% of all managed colonies in the United States. One of the preliminary
results of this research is that 100% of the sampled varroa mites (n = 39) had
amitraz resistant genetics.
Overall, although the early season trends in varroa mite populations
across the Maritime region seem well managed, beekeepers must remain vigilant
when monitoring for mites, and practice integrated pest management in all
aspects of their mite management. 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 one of our survey. We will be reporting on
trial two of our survey later this summer.
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
References
Fanelli, A.,
& Tizzani, P. (2020). Spatial and temporal analysis of varroosis from 2005
to 2018. Research in Veterinary Science, 131(January),
215–221. https://doi.org/10.1016/j.rvsc.2020.04.017
Sobkowich,
K.E., Berke, O., Bernardo, T.M., Pearl, D.L. and Kozak, P., 2025. Time series
analysis of Varroa destructor counts in Ontario honey bee colonies and their
association with weather variables. Journal of Apicultural Research,
pp.1-8.