The ATTTA team has now completed our regional Varroa mite survey and amitraz efficacy testing for the current year. This research is important to our Maritime industry as it provides an understanding of the Varroa mite levels across the region throughout the beekeeping season and indicates if both current Varroa management practices and treatment are effective at keeping levels under control. This week’s blog will provide a summary of the result for 2024, and a comprehensive report will be published online in the weeks to come.
ATTTA Varroa Mite Report 2024
This past season,
the ATTTA team completed Varroa mite sampling from a total of 23 different
commercial beekeepers from New Brunswick, Nova Scotia and Prince Edward Island.
These representative beekeepers manage a significant portion of Maritime honey
bee colonies, where 17% of Nova Scotia colonies are represented and between 25
to 30% of all New Brunswick colonies managed are represented. The survey
included samples from 25 apiaries, 81 colonies, and included a total of 167
samples.
As shown in
the graph below, the number of samples positive for Varroa mites increased by
61% from early-season (7%) to late-season (68%). The number of colonies above
the economic threshold increased by 8% from early-season (2%) to late-season
(10%).
The results
of the 2024 survey determined Varroa mite levels across the Maritime region
increase throughout the beekeeping season as expected, where there is an
increase in mites sampled between each trial. This makes early spring
monitoring and treatment for Varroa mites crucial because populations can
quickly get well beyond the economic threshold if waiting until the fall to
treat colonies again.
Conventionally,
with monthly monitoring, treatment is only indicated when the mite population
is at or above the economic threshold. However, beekeepers should remember that
current established economic thresholds need to be contemplated against the
changing climate and lengthening of seasons. Also, treatments should be applied
in consideration of the mite populations across an apiary and not individual
colonies. Beekeepers in the Maritimes report having low levels of mites across
an apiary with the exception of one or a small number of hives. This makes
frequent and representative monitoring important for beekeepers.
Additionally,
this past season, ATTTA tested the efficacy of Amitraz (active ingredient in
Apivar®) against populations of mites collected throughout the Varroa mite
survey. The results of the amitraz efficacy study for 2024 suggest low reduced
efficacy of amitraz for a limited number of mites that were assessed. The
efficacy level of amitraz was determined by calculating a resistance ratio
which compared the amitraz sensitivity of mites tested within ATTTA’s study to
a highly sensitive population of United States Department of Agriculture Varroa
mites. The resistance ratio was determined to be 3.75, where a population with a
resistance ratio under 5 has low reduced efficacy. However, multiple factors
could have impacted the study, and the results should be interpreted with caution.
One notable limitation is the relatively small sample size of mites that were
included in the study, which may not be representative of the entire mite
population. Additionally, the data was collected from just 2 beekeepers, which
further limits the generalizability of the findings. The reason only 2
beekeepers were included within the testing is that most beekeepers did not
have enough mites present to set-up a proper experiment replicate. Given these
limitations, it would be premature to make a conclusion about any level of
reduced efficacy to amitraz over the past 2 years, and the study needs to be
replicated with a larger sample size of mites and more beekeeping operations
represented.
Finally, the general trend observed is that with increasing
concentration of amitraz there is increased mortality (see graph below). In
other words, higher concentrations of amitraz are more effective at killing the
mites, suggesting an ongoing dose-response relationship between the amitraz
concentration and mite mortality. However, the sample size was too small to
have enough statistical power to report a significant interaction. So the 2024
results were less than conclusive as to the comparable effect of amitraz
concentration on mite mortality.
ATTTA plans
to continue this study to assess how the efficacy of amitraz changes year to
year, and the goal is to test a larger number of mites from more Maritime
beekeepers. It is critically important to extend the effectiveness of
amitraz-based products to control Varroa mites by practicing integrated pest
management.
Overall, the
results of the survey indicate that beekeepers are doing a good job at managing
mites in the Maritimes, and that current treatments continue to be effective
within the region.
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