Honeybees collect myrtle rust as food, study finds

A recently published study shows myrtle rust spores provide the protein and amino acids honeybees need to feed their larvae.

The study findings increase concerns that introduced honeybees could spread myrtle rust, which poses a serious threat to several New Zealand native trees, says lead author Sacchi Shin-Clayton, a former University of Auckland masters student, now at Cambridge University in the United Kingdom.

“Honeybees tend to forage on lots of different plants and go back to the hive when their furry bodies are completely covered in pollen.

“That behaviour is great for facilitating pollen spread and plant pollination.

“The same could happen with myrtle rust transferring between plants,” says Shin-Clayton.

At present, beekeepers often transport hives long distances to provide honeybees with new pollen sources, such as mānuka, she says.

Biosecurity initiatives for beekeepers could be needed to help to restrict the spread of myrtle rust, says Dr David Pattemore, a former University of Auckland senior lecturer and senior scientist at New Zealand Institute for Bioeconomy Science, who supervised the study.

“If beekeepers have their hives in an area that’s badly affected by myrtle rust, it’s worth considering a stand down period at another site, before moving the hives near native forest,” says Pattemore.

“Otherwise, the rust spores from the hive could drive a more serious outbreak in the forest.”

The research overturns previous understandings that honeybees only collect pollen and that their larvae only survive when fed on pollen, says University of Auckland Professor of Biological Sciences Jacqueline Beggs, who oversaw the research.

“This study also challenges the assumption myrtle rust is mainly spread by the wind, because it shows honeybees can move spores around the country,” says Beggs.

The research involved Shin-Clayton feeding royal jelly mixed with myrtle rust spores to honeybee larvae.

She found the larvae grew just as well on myrtle rust as they did when fed on pollen from favoured sources, including kiwifruit and willow.

The study also confirmed myrtle rust spores can remain viable in beehives for up to nine days.

Myrtle rust can kill plants and trees in the myrtle family, which includes native species, such as pōhutukawa, rātā and mānuka.

The fungal disease poses a risk of localised extinctions for some native plants, such as swamp maire and ramarama, says Shin-Clayton.

It also affects exotic species such as guava, feijoa, bottlebrush, lilly pilly, and eucalyptus.

Honeybees have been documented collecting myrtle rust from maire tawake, and there are reports of honeybees collecting the spores from ramarama and mānuka, says Pattemore, who is now managing director at Bushcast and Whakarongo Environmental.

Originally from Central and South America, myrtle rust was first detected in Kerikeri in Northland in 2017, possibly carried by wind from Australia, where it was first found in 2010. It has spread through much of the North Island and parts of the South Island, but tends to flourish in warmer climates, the researchers say.

Shin-Clayton says honeybees have well-organised colonies and communicate with each other about good food sources, which they then continuously target.

Myrtle rust spores resemble pollen grains – they are yellow, spherical and can be found on flowers, as well as on the leaves of infected plants, she says.

Beggs says the mutual benefit gained by the introduced honeybee, which has a new food source in New Zealand, and by the myrtle rust, which has a new means of long-distance dispersal, fits a pattern called “invasional mutualism”. This occurs when introduced species aid each other’s success, often exacerbating their invasion and harming native ecosystems, says Beggs.

“Myrtle rust is one of the most serious threats to native plants in the myrtle family.

“We know it’s had a devastating effect on plants in Australia.

“It’s fairly new in New Zealand and we don’t want it to run rampant, so it’s important to understand it better and consider ways to reduce the spread,” Beggs says.

The study was carried out in collaboration with Queensland University of Technology and Agri-Science Queensland. It was funded by the New Zealand Ministry for Primary Industries and the New Zealand Institute for Plant & Food Research.