Bees being able to smell trouble is a skill that could give them a fighting chance against the deadly Varroa mite.
Damaged Wing Virus can add to a bee colony's troubles, particularly during a bad varroa mite infestation. Photo: 123RF
New research from the University of Otago shows some worker bees are able to sniff the parasite out and better protect their colony.
The parasitic mites have been found to feed directly on honey bee fat stores and transfer numerous pathogens to the bee, including the deformed wing virus.
The study says most honey bee colonies of the type found in New Zealand could die within two years of varroa infestation without intervention.
Otago University Emeritus professor Alison Mercer worked with the team on the study.
"[Bees] have a fantastic sense of smell," she told Morning Report, adding they needed to know the smell of different flowers to be able to find food.
"They use their sense of smell extensively inside the hive because ... the hive is dark, so they're feeling their way around."
The adult Varroa mites are "sneaky", Mercer said.
"They camouflage themselves by making their body cuticles smell just like that of the bees and their host colony."
She said the research team was surprised that the bees could use their sense of smell to detect the mites; calling it varroa sensitive hygiene behaviour (VSH).
"Turns out some worker bees can detect Varroa mites as they are reproducing inside the brood cells."
Brood cells contain developing honey bees.
"Any worker bee that detects these Varroa smells inside these brood cells, they open up to the Varroa infested brood cell and they kill the developing bee inside, they remove all the cell contents including the mites. The key thing is it suppresses the reproduction of the mites."
Varroa mites are "sneaky" - Alison Mercer
Lead researcher Fanny Mondet - splitting her time between the National Institute for Agricultural Research in Avignon, France and the Department of Zoology at the University of Otago in Dunedin - assembled a team of researchers to understand further.
In a paper published recently in Nature Chemical Biology, Mondet and colleagues identify six varroa-related compounds (four ketones and two acetates) that trigger VSH behaviour.
"If the varroa-related compounds alone are presented to bees, all bees appear able to detect the odours. 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.
"In their defence against varroa, bees' ability to differentiate healthy from unhealthy hive odours is critical. In vulnerable colonies, a majority of worker bees fail to show this ability," she says.
She said it was critical, for breeding reasons, to identify colonies that showed high levels of VSH activity.
"In field trials, we were able to show injection of 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 assist greatly the breeding of bees with stronger resistance to the devastating impacts of the varroa mite."