As the tiny but deadly varroa mite (Varroa destructor) spreads within Australia's honeybee population, much of the concern so far has understandably focussed on the impacts on the agricultural and bee-keeping industries. However, a new study led by UNSW Sydney highlights the urgent need to understand both the threats and opportunities for native plants and pollinators.
In their paper published today in the Australian Journal of Botany, the researchers reviewed existing literature to specify the large knowledge gaps in our understanding of the interactions between native Australian plants, pollinators and the European honeybee (Apis mellifera).
"We have around 24,000 unique native plants, trees and shrubs in Australia," says the study's lead author, Dr Tom Le Breton, from the Centre for Ecosystem Science at the UNSW School of Biological, Earth and Environmental Sciences (BEES).
"And some of these natives, such as gumtrees, are pollinated in the wild by the honeybee, which is an introduced species."
While pesticide use, habitat destruction and climate change are already diminishing pollinator populations around the world, the varroa mite is speeding up the process for European honeybees. This mite— which was first detected in a sentinel hive at the Port of Newcastle in 2022—devastates honeybee populations. The mite feeds on their bodily fluids and babies, while spreading disease. Once the mite establishes itself in an area, populations tend to collapse.
However, it might not all be bad news.
"While the European honeybee has become the dominant pollinator for some native species, recent research shows that they can also have a negative impact on others, by stealing pollen or deterring more effective native pollinators," Dr Le Breton says.
"As Australia is the last honey-producing country to become infected with the varroa mite, we are in a unique position where we can review global experiences," he says.
"There is still time to set up monitoring systems, so we can determine what impact the decline of feral honeybees will have on native pollinators and plants."
A useful but feral animal
Honeybees were introduced to Australia in the early 1800s. While no long-term research exists on how the bees impacted native plant species back then, today they are widespread in feral populations, pollinating natives as well as harmful weeds.
"Our population of feral honeybees is among the highest recorded anywhere in the world," says co-author Dr Chantelle Doyle, also from the UNSW School of BEES. "They exist in up to 128 colonies per square kilometre in southern Australia, with as many as 50,000 individuals in each colony."
A 15-month multi-agency response was launched when the varroa mite first appeared in New South Wales 3 years ago. Despite efforts to eradicate it, the nation has now accepted the mite is here to stay. It has since spread beyond the borders—detected in Queensland only last week, and in Victoria late last year.
In other countries, the spread of the parasite has led to the loss of around 96% of feral honeybee populations within just a few years of its arrival.
What does this mean for Australia?
Such a large decline of a key pollinator species could change the pollination landscape. But with limited existing research, predicting what these changes will be and what they mean for native flora is a difficult task. By comparing current pollination patterns with those after the decline of honeybees, researchers could gain valuable insights into how native plants may adapt and how conservation efforts should be directed.
"Preparing for these changes is crucial," says Dr Le Breton. "Especially in regions such as Western Australia, where it will take longer for the mite to reach."
Honeybees are sometimes direct competition for native pollinators—other bees, birds, and mammals—often outnumbering these species.
The decline of feral honeybees could give any native pollinators that have struggled to compete a chance to reclaim their role in the ecosystem.
To better gauge what's possible, scientists now aim to gather data government partnerships and collaborations with conservation groups. This includes a citizen science project set up by the UNSW scientists in collaboration with Western Sydney University: Honeybee visitation and native plant pollination Australia.
The buzz with native bees
Without honeybees dominating flower visits, native insects may be able to pollinate more effectively, leading to plant-pollinator communities closer to those that existed before colonisation. This includes more than 1200 native bee species—some of which have unique features that honeybees don't. Native bees also aren't affected by the mite.
Small native bee industries already exist in New South Wales and Queensland.
"Some native bees, like the Reed bee, use thoracic vibrations—or, buzz pollination— where they vibrate their thorax really quickly," Dr Doyle says.
"This releases the pollen from the anthers of the flowers—the tight little tubes that hold the pollen," she says.
"So buzz pollinators are really effective—way more effective than honeybees, which is one of the reasons why honeybees are detrimental to some species of plants."
"The pollen that sticks to the bodies of honeybees is from plants where the pollen is looser and more exposed—like with weeds."
A loss of feral honeybees could therefore help reduce the seed set of harmful weeds and slow their spread.
The future of pollination in Australia
With a decline in feral honeybee populations, there may still be some rare or threatened plants that struggle, especially with ongoing ecological pressures such as land clearing, fire regimes and climate change.
But the risk of plant decline is still poorly understood. As the window for measuring the effect of a dwindling feral honeybee population starts to close, "we urgently need more research and data on how different plant and pollinator species will respond," says Dr Doyle.
"For example, one detrimental impact from a decline in feral honeybees is on mangroves. Honeybees have become the dominant pollinator for Australia's east coast mangrove forests," she says.
These key habitats—crucial for fisheries as well as coastal protection and carbon sequestration—are already under threat from rising sea levels with massive diebacks.
After bushfires, feral honeybees are also effective at pollinating recovering plant species in affected areas.
The authors says national parks and wildlife agencies will need potential strategies to manage feral honeybees infected with the mite in ecologically significant areas.
For now, conservation efforts could include planting more pollinator-friendly gardens, protecting habitats, or even manually pollinating endangered plants.
"We need long-term studies on pollination interactions, impacts on threatened species, and the ecosystem-wide effects of honeybee decline," Dr Le Breton says.
"Australia has a rare opportunity to learn from their experiences and act to protect its unique ecosystems."
