Varroa Treatment Resistance Uncovered in Australia – “Shot Across the Bows” for NZ

Three and half years on from first finding varroa in Australia, authorities have detected a gene mutation in the parasite which is resulting in lower susceptibility to several common treatments. Has this ‘resistance’ developed in such a short period? Is it the result of a separate, parallel, mite incursion? Or has it just been missed to this point? Australian beekeepers and scientists are searching for answers, while experts in New Zealand say the news should put Kiwi beekeepers on notice.

First a northern New South Wales beekeeper raised the alarm in February when it appeared his varroa treatments had not had the desired effect. Testing on those mites showed a common mutation also found in North America, Europe and Eurasia resulting in synthetic pyrethroid resistance was present. In March, similar mutations were found in southeast Queensland in populations linked to the first discovery.

Australian Honey Bee Industry Council CEO Danny Le Feuvre says there is a “strong likelihood” that the recent discovery of synthetic pyrethroid resistant varroa is down to a new varroa population entering Australia.

“If it is truly locally grown resistance that is concerning and equally, if it is a new mite population, that is also very concerning,” says Bianca Giggins, who has been at the front line of Australia’s varroa response as first the Australian Honey Bee Industry Council’s (AHBIC) varroa coordinator and now industry development manager.

Miticide treatments Bayvarol, which has the active compound of flumethrin, and Apistan, active compound tau-fluvalinate, fall into the synthetic pyrethroid category. Both are registered for use in Australia and New Zealand.

Homegrown or Imported

While nothing has yet been confirmed and testing of Australia’s varroa population is ongoing, there is a strong hunch as to how this mutation came to be.

“At this stage, based on the current limited testing, resistant mites appear to be localised to a relatively small geographic area and have mainly been identified in situations where treatments have not performed as expected,” AHBIC chief executive Danny Le Feuvre has told their members.

“Testing of apiaries around the identified resistant apiaries has shown no mutations and a high level of susceptibility to Bayvarol. This is important as currently the tested mites have either been 100% resistant or highly susceptible with no in-between, which is not what you would expect if it was locally grown resistance.

Example of resistance development occurring due to repeated use of same chemical mode of action; red = resistance mites, yellow = susceptible mites.

“This indicates there is a strong likelihood that this could be a new varroa population entering Australia, rather than resistance developing from the existing mite population. That distinction matters, because it suggests this is not yet a widespread national issue – but it does reinforce the ongoing importance of biosecurity vigilance.”

Giggins says as part of Australia’s “transition to management” of the mite over 100 educational workshops have been delivered and around 50% of the country’s 47,000 registered beekeepers have been reached by a “world class extension network” which has had an “emphasis on best practice varroa management, chemical rotation, Integrated Pest Management (IPM) strategies and business resilience”.

“We have also observed mixed and variable application of this new information among industry, but overall, Australia's beekeeping industry has built new management skills in a very short timeframe which we are very proud to have achieved,” Giggins says.

Several New Zealand-based beekeeping supply companies’ sales data into Australia would seem to support the belief that, on the whole, Australia beekeepers’ management practices are not likely to have created pyrethroid resistance in such a short period of time. IPM (principally rotating treatments between chemical families) has largely been undertaken believe both New Zealand Beeswax general manager Nick Taylor and Ecrotek Beekeeping Supplies chief executive Greg Smith.

Within the NZ Beeswax range, Taylor says Apivar, with the active compound amitraz, has been “by far” their biggest seller to Australia, but there is a “big three” rounded out by Bayvarol and Formic Pro. Oxalic acid is also known to be popular among Australian apiarists, many of who chase a long honey season, as it can be safely used while supers are preset. Bayvarol also has a “friendly” label as pertaining to use alongside honey boxes, plus it was used heavily by authorities and beekeepers alike during the early stages of the varroa incursion which began June 2022.

“There has been a big reliance on Bayvarol and so there is disappointment this gene has been identified,” Smith says.

While that may be the case, Taylor believes most beekeepers have followed a “logical progression” towards an IPM approach.

“They had a plan as an industry and, to their credit, they have moved to an IPM style rotation. If you take a step back and look at the industry as a whole, they have been adopting best practice and progressing step-change over time in a logical fashion,” Taylor says.

“Unfortunately, in any industry, there is going to be a pocket of individuals who may have ruined it for everyone else.”

Lessons for New Zealand

Avoiding that “ruin” in New Zealand should be the focus for Kiwi beekeepers and Smith calls the news out of Australia a “shot across the bows” on this side of the Tasman. While resistance to synthetic pyrethroids has been anecdotally suggested by some New Zealand beekeepers for several years, genomic testing has not identified the corresponding mutation in the varroa population.

No one has looked more closely than John Mackay, technical director at Gisborne lab dnature Diagnostics and Research. Coincidentally, in February, Mackay was the lead author on publication of an article detailing a new technique developed by their lab to test for such treatment resistance. That research saw more than 1000 varroa mites, collected from numerous regions around New Zealand, tested over an eight-year period for resistance to Bayvarol and Apistan. No resistance was found.

“The interesting thing about pyrethroid resistance is the major resistance found around the world is localised to three sequential DNA bases that make up one amino acid, which makes a protein. It’s called L925. There are combinations, but the Australians have two of the three mutations present that we look for,” Mackay explains.

Example of resistance management involving rotation of chemical mode of action; red = resistance mites, yellow = susceptible mites.

He says that raises the question about whether the Australian varroa mutated to become pyrethroid resistant, “which would be remarkably quickly, even if just solely using one treatment,” or have they had a new incursion, such as the AHBIC leadership are leaning towards.

Honey bee imports are not allowed into New Zealand, and a strict biosecurity regime is undertaken, minimising the risk of spread of Australia’s pyrethroid resistant varroa across the Tasman. Therefore, if New Zealand’s beekeepers rotate between varroa treatments, and follow label instructions, a mutated and resistant varroa should be avoided.

“Generally New Zealanders have used commercial products, of know efficacy, rotated treatments and used best practice. Now we are bringing in increased mite monitoring … if those best practices are championed then I don’t have any undue concern, due to our strict biosecurity,” Mackay says.

Smith sees the consumption habits of Kiwi beekeepers through Ecrotek Beekeeping Supplies’ sales.

“The reason we are in reasonable shape here is the rotation of treatments has been good, and it needs to continue to be, combined with better on-label use. We hear some amitraz-amitraz back-to-back treatments are going on and that is something the industry should be careful of,” the Ecrotek CEO says.

“All of us as beekeepers get in those situations where you get the dilemma, this is better for me right now, but this other option is better for the industry and avoidance of creating sub-lethal environments for varroa. We need to continue to choose the latter.”