A future weapon for Canadian beekeepers may be available in the battle against Varroa mites. Our southern neighbors in the USA have a new product which has been submitted for EPA approval and is expected to be accessible for beekeepers soon. This new registration, if approved, will be a bioinsecticide purported to be safe for humans and bees as well as highly effective against Varroa mites. Read along as we explore a new category of miticide which may be an effective tool to help manage mite populations.
Varroa Control: A new class of miticide!
Vadescana is a new active ingredient which the U.S.
Environmental Protection Agency (EPA) has proposed for the control of Varroa
mites. The EPA is prioritizing product registrations for active ingredients
targeting Varroa mites. So, there is an
expectation that vadescana will be available to US beekeepers in the very near
future. Once approved, the developer and
manufacturer, Greenlight Biosciences ™, will distribute the product for US
beekeepers. It is sold under the name,
“norroa” in a sucrose pouch (see figure).
What is unique about this acaricide is the active
ingredient. It relies on an innovative RNA
formulation which has high species specificity 1. Ribonucleic acid, or RNA, is present in the
cells of all living organisms and is typically a cellular messenger
(mRNA). Vadescana uses a particular form
of RNA called double stranded RNA (dsRNA). Double stranded RNA, often
associated with viruses, can be modified to interfere with gene expression in a
target organism. The active mechanism of
dsRNA, used as a pesticide, is to silence certain genes in the targets species which
in turn disrupts or interferes with specific cellular functions. Hence
the term interference RNA, or RNAi, is sometimes applied to these compounds.
Specifically in Varroa mites, vadescana targets the
calmodulin gene sequence. This gene is
linked to a number of cellular functions but in relation to the control of Varroa
mites, the silencing of this gene inhibits female reproduction 2. Due to the unique sequence of the target gene
in Varroa mites, generally other species with the calmodulin gene should not be
affected. The exception to this could be
other close relatives, from the class Arachnida, which may suffer off-target
effects. Interestingly, in this category
are tracheal mites and Tropilaelaps mites.
 |
| The application of the product "norroa™" containing the active ingredient vadescana. |
In Canada the use of pesticides and pest management products
is regulated by Health Canada’s Pest Management Regulatory Agency (PMRA). They are tasked with protecting human health
and the environment, specifically when it comes to registering pesticide
products. According to a PMRA
information note there are currently no dsRNA miticide products available or
under review for registration in Canada.
There are limited examples of this technology being used in agriculture
in Canada. Growing modified corn which
expresses dsRNA for the control of the Western Corn Rootworm has been approved. This is a systemic product, in that the plant
itself produces the dsRNA, rather than a direct application required for mite
control. The type of application that
would be for the control of Varroa mite is referred to as spray induced gene
silencing. The PMRA is expecting
applications for the registration of dsRNA products and has a working group
looking at these technologies in anticipation.
Future applicants submitting products for registration must include data
on toxicology, and both occupational and environmental hazards. Currently the use of spray-application dsRNA-based
pesticides, is not permitted in Canada with the one exception of when used for
research purposes.
Concerns over the efficacy of conventional acaricide
products for the control of Varroa mites creates anticipation when new products
are proposed. These may be entirely new
compounds, such as vadescana, or new applications of already approved active
ingredients. An example of the latter
would be oxalic acid / glycerin products currently being considered for
registration by PMRA. The additional
tools are necessary for beekeepers to combat mites, especially in consideration
of the challenges presented by climate change and reduced chemical miticide
efficacy. It is unknown how quickly the
mites will develop resistance to vadescana.
One research trial has indicated that resistance can develop as quickly
as 7 – 11 generations in targeted insects 3. This would indicate that dsRNA, if registered
in Canada, will be part of an overall IPM approach to managing Varroa mites.
RNAi, as a new mode of action bioinsecticide, may provide
solutions to overcome some of the shortcomings of chemical miticides,
especially related to overuse and resistance. There are real advantages to
these products in being target specific and quick to degrade in the
environment. There are still questions on
long term efficacy and costs of this novel treatment. The current method of application, sucrose pouch,
indicates that this will not be a product used during honey production. As an additional management tool for Varroa
mites, dsRNA has potential as a upcoming miticide for use by Canadian
beekeepers! One to watch for the future.
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 and Reading
1. 1. Bulgarella, M., Reason, A., Baty, J.W.,
McGruddy, R.A., Gordon, E.R., Devisetty, U.K. and Lester, P.J., 2025. In Silico
Analysis of Potential Off-Target Effects of a Next-Generation dsRNA Acaricide
for Varroa Mites (Varroa destructor) and Lack of Effect on a Bee-Associated
Arthropod. Insects, 16(3), p.317.