Scientists have identified naturally occurring compounds which induces a cleaning response among some worker bees, killing juvenile varroa mites.
The University of Otago researchers are now looking at how to replicate the six relevant compounds they have discovered, and a way to deliver them to hives from which beekeepers can selectively breed bees that have this trait.
Emeritus Professor Alison Mercer of the university’s Department of Zoology says varroa mites reproduce in brood cells, but researchers have identified some worker bees can sense where the mites are using these compounds, then open those cells and pull out the contents, including the mite, killing it.
Unfortunately, they also kill juvenile bees forming there, but Mercer says this varroa sensitive hygiene behaviour (VSH) is a trait breeders can utilise.
“Within any colony you get worker bees, some of whom are able to detect varroa mites,” Mercer said.
By identifying worker bees and breeding from their colonies, she says beekeepers can develop bees that will stand up to the varroa mite.
This discovery solves a problem that has confounded solutions to confront the varroa mite infestation.
“Standing in the way has been trying to identify colonies that show varroa resistance,” she said.
Mercer says six years of work by lead researcher and University of Otago Department of Zoology doctoral candidate Fanny Mondet revealed that adult varroa can camouflage their presence in a hive by mimicking the smell from within the colony.
But juvenile mites cannot do that, making them vulnerable to attention from worker bees that have the VSH trait.
“We know that if we take the compounds into a colony in the field and inject the compounds into cells, when we return the next day a colony with strong resistance will have all the cells opened up,” she said.
Without intervention, infected honeybee colonies die within two years of varroa infestation.
The key has been identifying the six compounds that trigger VSH behaviour.
In a paper published recently in Nature Chemical Biology, Mondet and her research colleagues identified four ketones and two acetate compounds that provoke this behaviour.
A French researcher, Mondet worked between France and NZ and while here, liaised with beekeepers throughout NZ.
Now back in France, she says in a statement that the level of compounds found in varroa-infested brood cells is a reliable indicator of the numbers of juvenile mites present, which enables worker bees to selectively target those that are infested.
“If the varroa-related compounds alone are presented to bees, all bees appear able to detect the odours,” Mondet said.
“However, not all bees are able to tell the difference between the smell of healthy brood odours and the smell of brood odours containing varroa-related compounds.”
To confront varroa it is critical for worker bees to differentiate healthy from unhealthy hive odours, but for beekeepers to use this natural process is difficult, time-consuming and with no guarantee of success
“In vulnerable colonies, a majority of worker bees fail to show this ability,” she said.
“In field trials, we were able to show injecting the varroa-related compounds into brood cells induces responses in worker bees that mimic intrinsic VSH activity in bee colonies.
“A simple and reliable bioassay of this kind has the potential to greatly assist the breeding of bees with stronger resistance to the devastating impacts of the varroa mite,” she said.
The next stage of the research is to develop a cheap and easy delivery system, allowing beekeepers to identify resistant colonies from which to breed from.