After over 20 years in New Zealand, varroa’s momentum appears to be picking up, hitting hives harder in the past year.
More than two decades after it arrived in New Zealand, varroa mite is being reported as the main reason behind a significant jump in beehive colony losses.
MPIs colony loss survey this year covered almost 50% of the country’s hives and beekeepers have reported overall loss rates from last winter were 20% higher than the year before. Compared to the first year of the survey in 2015, the loss rates are 62% greater.
This survey marks the first time varroa mite has been reported to be the main cause of colony loss, with issues over queen bee problems typically the main driver of winter losses in the past.
Total colony loss rates have been estimated at 13.5%, of which almost half or 5.1% of losses were attributable to varroa. This is significantly up on the 1.6% varroa loss incurred only five years ago.
Varroa was first detected in NZ beehives in April 2000 in South Auckland and has since spread progressively throughout hives, requiring all commercial hives to undergo a level of treatment in order to keep bees alive.
Apiculture NZ Science and Research Focus Group chair Barry Foster said as a country, NZ has done exceptionally well trying to slow varroa’s spread over the past 22 years.
This was in part by ensuring only valid effective treatments had Agricultural Compounds & Veterinary Medicine (ACVM) approval for use.
But it was now endemic in NZ and he feared it was building a momentum that made it more virulent and intense in terms of the damage it inflicted upon hive populations.
“We have always been told varroa would grow resistant to some of the chemicals used,” Forster said.
He said at this stage that resistance was only emerging and not widespread.
However, the density of hives in NZ was also exacerbating varroa’s spread.
At almost one million hives, NZ has more than Australia and population numbers meant failure to treat a hive for varroa could see it spread relatively quickly through populations.
“The viruses that varroa introduces are also becoming more virulent. We find it takes less varroa to cause hive collapse than it did 20 years ago. We are having to close up our timing of treatments. Where it used to be once every four months, it may now be once every three,” he said.
Regionally bee colonies in the upper North Island were likely to be more affected by varroa, largely on account of hive density and use for pollination. The Waikato, Bay of Plenty, East Coast and Hawke’s Bay regions reported an 18.7% winter loss rate against the national average of 13.6%, and 8.6% of colonies were lost to varroa compared to 5.3% nationally.
He believed there was a need for more monitoring of hives by beekeepers, with the risk of complacency creeping in with some operators. The survey indicated about a quarter of beekeepers do not undertake any active varroa monitoring and 4% are not treating for varroa at all.
“There is no shortage of material out there to keep beekeepers informed on what to be looking for,” he said.
This year’s Apiculture NZ conference in June would reveal some of the new treatments emerging onto the United States market, but Foster estimated they could still be four to five years away for NZ.
“Varroa is a formidable enemy. But we are fortunate to have a very good survey response to give us good numbers on its effects,” he said.