Richard Musgrove
Plant ecologists are having a fresh look at the impact of the varroa mite which might change the relationships between bees and local native vegetation.
The introduced European honeybee, although feral, is well established across Australia.
Varroa mite, a European honeybee parasite, poses a threat to the feral honeybee population on which much of our agriculture and bee-keeping industries depend. Native bees cannot host mites, due to their different biology.
Opportunities and challenges brought about by the European honeybee and the mite are discussed in a just published review by UNSW researchers, in the Australian Journal of Botany, by CSIRO Publishing.
Varroa mites have 8 legs and are related to spiders. The 2mm long varroa mite females sport a scallop-like red shell but the males are yellowish-white. They feed on adult bees’ bodily fluids and larvae and carry diseases such as deformed-wing virus. Infestations have caused hive collapse and honeybee declines world-wide.
Varroa mite was first detected in New South Wales in 2022 and recently in Victoria and Queensland, and the focus is on management, rather than eradication, says CSIRO’s Dr John Roberts, who also adds that deformed-wing virus has not yet been detected in Australia.
“We have around 24,000 unique native plants, trees and shrubs in Australia,” says lead author, Dr Tom Le Breton, from BEES (School of Biological, Earth and Environmental Sciences,) at UNSW.
“And some of these natives, such as gumtrees, are pollinated in the wild by the honeybee, which is an introduced species.”
Native bees are also more efficient pollinators.
“While the European honeybee has become the dominant pollinator for some native species, recent research shows that they can also have a negative impact, by stealing pollen or deterring more effective native pollinators,” Le Breton says.
“Some native bees, like the Reed bee, use thoracic vibrations—or, buzz pollination— where they vibrate their thorax really quickly,” says coauthor, Dr Chantelle Doyle.
“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.
“The pollen that sticks to the bodies of honeybees is from plants where the pollen is looser and more exposed—like with weeds.”
Bees and varroa mite – what have we learned?
A loss of feral honeybees could therefore help reduce the seed set of weeds and slow their spread, says Le Breton
But what of those plants now mostly pollinated by feral bees? What happens to them is poorly understood, say the researchers
“We urgently need more research and data on how different plant and pollinator species will respond,” says 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.
Such teeming ecosystems, already subject to massive diebacks caused by rising sea levels, also function as carbon sinks and provide coastal protection.
Feral bees are also effective at pollinating recovering plant species in bush-fire affected areas, says Le Breton.
State and federal governments need strategies to manage mite-infected feral honeybees in ecologically significant areas, he adds.
“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.”
