Synthetic Chemical Treatment Options for Varroa Mites

Thursday 15 October 2020

Last week we talked about some of the principles of IPM.  One of the fundamentals of this strategic approach to pest management is to have a ‘tool box’ of treatment options.  Chemical acaricides are an important means of controlling Varroa mites, so are worth a few words in this week’s blog.

A reminder that 'The King of Heather Honey', Murray McGregor, will be presenting a webinar this Saturday for the Nova Scotia Beekeepers Association.  Details on how to attend below.

Synthetic Chemical Treatment Options for Varroa Mites

Beekeepers have only a few options when it comes to chemical control of Varroa mites but luckily in Atlantic Canada we have access to the highly effective Apivar® manufactured by Vetò-Pharma.  The active ingredient in this synthetic miticide is amitraz from the chemical class formamidines.  Currently, no mite resistance to this treatment has been reported in Atlantic Canada and research done by ATTTA in 2017 confirmed its efficacy.  In other areas, resistance has been reported!  This is of concern, as an alternative will be required when Varroa mites in our region inevitably show resistance.

All the synthetic acaricides available to beekeepers come from three chemical classes: synthetic pyrethroids, organophosphates and formamidines.  Historically, our region’s beekeepers treated mites with fluvalinate (Apistan®) which comes from the chemical class of synthetic pyrethroids.  In Canada, it has been documented that mites have resistance to this treatment but work by ATTTA in 2017 showed it was effective against mites in our region.  Although, those whose memories stretch back to the winter of 2007 / 08 will recall that the high winter losses reported that year were largely attributed to mite resistance to the then commonly used Apistan®.  This resistance, first reported in 2001, resulted in the emergency approval of coumaphos (CheckMite®) in Canada.  The efficacy of this treatment was short lived and resistance to this miticide, from the organophosphate chemical class, was soon reported.

A relatively new treatment, Bayvarol®, was approved for use in Canada in late 2016.  Both Bayvarol® (active ingredient: flumethrin) and Apistan® (active ingredient: fluvalinate) are synthetic pyrethroids of the same chemical class.  For this reason, it is recommended that these two treatments are not used consecutively within an IPM approach as this could result in cross resistance with these similar chemicals.  Also, as there is already reported resistance to Apistan®, there are some concerns with resistance to Bayvarol®.

Since it was approved for use in 2012, amitraz (Apivar®) has been the go-to chemical treatment for Varroa mites and no new chemical classes have been approved.  But as discussed above, new treatments are required once widespread resistance is reported.  As an example of a chemical treatment for the future, lithium hydrochloride holds some promise.  Work done at the University of Hohenheim, Stuttgart, Germany proposed the use of lithium hydrochloride (LiCl) in a paper published in the journal Nature Scientific Reports1.  A serendipitous discovery indicated that LiCl caused mite mortality leading researchers to investigate further.  Since the first publication of these results in 2018 many questions remain unanswered such as the overall environmental impact of LiCl, correct dosage and the most effective method of application.  Additionally, there are concerns that higher concentrations of LiCl are lethal to both adult and larval honey bees.  Researchers from this team reported as recently as this week, at the 16th  COLOSS eConference 2020, that they are still developing LiCl as a treatment.  There is a great deal of work required before this could become approved for use by beekeepers.

New treatments take years and resources to develop, so preserving current ones is important.  Using only as directed and following IPM strategies to preserve efficacy and prevent the development of resistance is the responsibility of individual beekeepers and our industry.  Beekeepers are encouraged to use alternatives, such as organic acids as well as cultural and physical controls to prevent overdependence on chemical acaricides.

1 Ziegelmann, B., Abele, E., Hannus, S. et al. Lithium chloride effectively kills the honey bee parasite Varroa destructor by a systemic mode of action. Sci Rep 8, 683 (2018).

Please see the attached video clip by Alex Crouse, NSBA President, and Murray McGregor, Fall Technical Session Keynote Speaker, providing a teaser of what is to come for the VIRTUAL NSBA Fall Technical Session this Saturday, October 17th from 10AM-12PM.

Go along to the NSBA Association website for details on how to attend!

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