The varroa mite, a major honeybee parasite, was discovered in biosecurity surveillance hives at the Port of Newcastle on Friday.
The pest affects every other major beekeeping area in the world, but has never established itself in Australia before. The discovery has sent New South Wales into bee lockdown – with no honeybees allowed to be moved across the state – as authorities aim to eliminate the parasite. What threat does the mite pose to Australia?
What is the varroa mite?
Varroa destructor is a brownish-red, sesame-seed sized mite that feeds on honeybees.
Dr Katja Hogendoorn, a research associate at the University of Adelaide said the mite “jumped ship from Apis cerana [the Asian honeybee], where it was relatively harmless, to Apis mellifera [the European honeybee]. The European honeybee doesn’t have a good defence against it.”
Since the early 20th century, the mites have spread from Asia to places including North America, the UK, New Zealand and Hawaii.
Although the mite is small – about 1.5mm wide – it is one of the largest parasitic mites in the world relative to its host, said Dr Cooper Schouten, a lecturer at Southern Cross University. “For a human, it would be like having a dinner plate-sized tick on you.”
“Although varroa mites can feed and live on adult honeybees, they primarily feed and reproduce on larvae and pupae in the developing brood, causing malformation and weakening of honeybees as well as transmitting viruses.”
The mites eat the fat body – a type of insect tissue – of adult bees and larvae. If untreated, a varroa mite infestation will cause a honeybee colony to die.
“What ends up happening over time is that the more the bees become weak, their life span is reduced and so there’s less bees collecting food – nectar and pollen. They become more susceptible to other pests and diseases and eventually the population dwindles to the point of no return,” Schouten said.
Hogendoorn said the mite was, damagingly, a vector and incubator of honeybee viruses. “Some honeybees are not going to die because of the mite, but most will die because of the viruses transmitted.”
The mite is a known vector for at least five honeybee viruses. “The virus that is most feared is called the deformed wing virus,” Hogendoorn. “We don’t have it here in Australia and we don’t know whether these bees that came in with the mites have also brought the virus.”
What is the threat if the varroa mite spreads across Australia?
“Australia is one of the last countries in the world where we don’t have this mite yet. So the potential impact is very significant,” Schouten said.
“These mites have been associated with significant colony losses globally. The potential impacts have been estimated at about $70m to the Australian honeybee industry.
“If managed honeybee populations decline there will be corresponding declines in supply for around a third of the food we eat, which means increased prices for food,” he said.
Hogendoorn added: “We might see shortages of these honeybees for pollination for a while … The demand for hives for pollination will go up.”
Varroa mites spread rapidly in New Zealand, where it was first detected in 2000. “Six years later it was all over the north and south island. It was really, really invasive,” Hogendoorn said.
Will it affect native bees?
Varroa mite is a parasite specific to two species of honeybee, and should not attack Australia’s native bees, of which there are more than 2,000 species.
But there is a possibility the mite could introduce new insect viruses to Australia. “The viruses that are spread might get into the landscape and … get into native bees, but we don’t know enough yet about whether they will cause disease there,” Hogendoorn said.
“The honeybee is an introduced species that went feral and is really invasive,” she added. “Chances are that the mite will decimate the feral population, with benefits for many of Australia’s native ecosystems.”
Can varroa mites be treated?
“Beekeepers in other countries, such as New Zealand, have been successfully managing varroa for decades, and so there are developed options for its management,” Schouten said.
Overseas, beekeepers manage varroa mites by treating hives with pesticides made from synthetic or naturally occurring compounds. Some cannot be used when honey is being produced, to minimise contamination.
Other management options include non-chemical techniques such as heating hives to around 40C, which does not kill the honeybees but causes the mites to die.
Treatment methods have varying degrees of effectiveness, and also require beekeepers to monitor mite numbers.
Are there alternative pollinators?
“Where the conditions are good we can get about one-third pollination by native bees and other insects,” Hogendoorn.
“Those other bees need support in the landscape. They can’t live off the crop alone because they don’t store honey and pollen. We need to plant food for bees for when the crop is not in flower – [for example] wildflower strips along crops.”
But Schouten said there were currently no alternatives for honeybee pollination at the scale required. “Honeybees contribute around $14.2bn annually to crop production through pollination,” he said.
Experts said Apis cerana, the Asian honeybee, was not a viable agricultural alternative in Australia. It is found in north Queensland and is considered an introduced pest species.
“The Asian honeybee is difficult to manage,” Hogendoorn said. “It absconds very quickly – it has small colonies and is quickly moving. They’re not by far as handy for crop pollination as European honeybees are.”
