Frans Laas, a scientist and president of the National Beekeepers Association, is also operations manager of Betta Bees Research, a company of 20 shareholder beekeepers from throughout the country who manage about 11% of all New Zealand’s honey bee colonies.

At a recent varroa workshop in Otago, Mr Laas outlined a promising pilot study the company is working on to test natural resistance of some colonies to varroa mite invasion.

Scientists know some bees that are more varroa tolerant than others tend to have better hygienic behaviour, Mr Laas said.

“We know that bees that express strong hygienic behaviour have an ability to dig out diseased or defective larvae and remove it from the colony,” he said. “Some bees express that behaviour better than others.”

Previous studies have shown that some bees have a better sense of smell and are able to detect varroa mite nymphs in closed cells, uncap them and remove the host pupa, causing the immature mites to die.

Another factor in varroa tolerance is the ability of the colonies to cause increased reproductive failure in the adult mites. This is referred to as Suppressed Mite Reproduction (SMR) and, combined with strong hygienic behaviour, results in the colonies improved ability to tolerate the presence of the mite.

Betta Bees’ pilot study started in 2007 when bees exhibiting strong hygienic behaviour were crossed amongst themselves to create a closed population. Hives were then sent to the North Island where they were exposed to varroa and left untreated through until autumn.

The last frame of sealed brood in each hive was then examined for varroa mite infection under the microscope, a monotonous and time-consuming job.

“What we found was that if bees could keep varroa mite infection rates below 15% of cells infected, they were able to tolerate mites reasonably well,” Mr Laas said. In hives with infection rates of 15% or less, the SMR rate rose dramatically.

The conclusion from the pilot study suggests selecting for hygienic behaviour increases the probability of finding improved varroa tolerance and consequently increased levels of SMR, which makes it possible to start breeding relatively highly varroa resistant colonies, Mr Laas said.

Now that legal restrictions have been removed against transporting bees from varroa infected regions south, Mr Laas would like to introduce genetic material from their North Island experiment into their full breeding programme, without hastening the southern spread of varroa.

“What we’re trying to do is take relatively varroa tolerant queens, take drone semen from their daughters and incorporate it back into the main pool, so the genes are spread rapidly through the breeding population, and repeat the process every year.

“It is a slower process, but we believe it is a far more sustainable way of managing varroa,” he said. “Chemical treatment is inevitably a dead end as a management tool.”

Betta Bees will maintain its current selection parameters to breed bees with a quiet temperament, good honey production and resistance to other diseases like chalkbrood and sacbrood.

The beekeeping industry maintains there is no “silver bullet” solution to varroa, but Frans Laas sees selective breeding as another weapon in the war against the parasite.

Selection for varroa resistance is relatively straightforward, but, unfortunately, most beekeepers don’t have the time to do it themselves, he said.

“We’re using relatively simple science to achieve some quite dramatic changes,” Mr Laas said. “It’s definitely a way forward.”