New research published in NeoBiota has found that the Western honey bee - an introduced species to Australia - and the devastating, invasive plant fungus known as myrtle rust (Austropuccinia psidii) may have formed a mutually beneficial relationship known as an "invasional mutualism."
Myrtle rust is notorious for devastating ecologically and culturally significant native plants in the Myrtaceae family, putting 17% of Australia's endemic vegetation at risk. While rust fungi generally rely strictly on wind to spread, researchers discovered that bees may actively forage on the bright yellow fungus spores, packing them into their pollen baskets and carrying them back to the hive just as they would regular pollen.
Through a series of experiments, the team made three significant findings. Firstly, the rust spores proved to be quite nutritious. They contained over 22% protein and all 10 essential amino acids, meeting the threshold required for bee colonies to survive. In fact, the fungus matched the nutritional quality of high-value floral pollen, like willow pollen. In laboratory feeding trials, larvae raised on a diet of myrtle rust spores grew up perfectly healthy, developing at the same speed and reaching similar body weights as bees raised on a traditional high-quality pollen diet. As the researchers explain:
These findings suggest that spore foraging may not be an aberration, but a viable foraging strategy for honey bees.
And perhaps the most alarming discovery is that the myrtle rust spores remain viable and capable of causing new plant infections for at least nine days inside a beehive which could pose significant biosecurity risks.
A Devastating Ecological Feedback Loop
This discovery challenges the assumption that invasive species always act independently, and it carries major environmental consequences. As myrtle rust kills off keystone taxa in the Myrtaceae family, such as eucalypts, paperbarks, and other ecologically and culturally significant species, particularly in Australia, fewer flowers and less pollen become available for bees to forage on. Beyond the direct biodiversity loss, as the fungus kills these plants, fewer flowers and less pollen are available for the bees.
"Under such conditions, bees may increasingly turn to alternative protein sources, such as fungal urediniospores," the researchers explain. This could set off a devastating ecological feedback loop. "Over time, this dynamic may destabilise plant-pollinator networks and forest regeneration, particularly in regions with high Myrtaceae endemism." They add: "While generalist foragers like A. mellifera may buffer their colony health by switching to spores or non-Myrtaceae pollen sources, the long-term ecological cost could be substantial, especially for specialist pollinators that lack such flexibility."
The risks extend beyond ecosystems. Because spores remain viable inside a hive for over a week, commercial beehives - regularly transported across the country over three to seven days to pollinate crops - now represent a significant pathway for human-assisted spread of the pathogen.
As the lead author, Sacchi Shin-Clayton (University of Cambridge) emphasises:
Apis mellifera is an introduced species used as a commercial pollination agent worldwide, and shifting honey bee colonies between agricultural sites to boost pollination has become a standard practice. This reliance on honey bee colonies and shifting between multiple sites is quite concerning, given the demonstrated interaction between A. mellifera and myrtle rust, and its longevity within colonies.
Despite this, current biosecurity strategies for managing myrtle rust do not account for the movement of commercial beehives, leaving a critical gap in disease management approaches.
We propose that honey bees be explicitly considered in both epidemiological models and the formulation of management and containment strategies,
- the researchers urge.
Recognising pollinators as potential vectors of invasive plant pathogens is an essential next step - one that could prove critical for protecting Australia's vulnerable native forests.
Original source:
Shin-Clayton S, Mortensen AN, Beggs JR, Buxton MN, Hauxwell C, Bateson MF, Jochym M, Pegg GS, Pattemore DE (2026) Honey bees as potential vectors of the invasive rust pathogen Austropuccinia psidii: nutritional mutualism and implications for pathogen spread. NeoBiota 106: 75-90. https://doi.org/10.3897/neobiota.106.169027
