Mite fight: Bees face parasite threat

Now the threat has sharpened, with Agriculture Victoria confirming in May that mites at a Victorian apiary had developed resistance to pyrethroid treatments, the insecticide beekeepers have long relied on to combat outbreaks.

By early June, the same mites had tested positive for resistance to formamidine-based treatments as well, wiping out the two major chemical groups available to Victorian beekeepers in a matter of weeks.

It follows resistance already confirmed in NSW and Queensland earlier this year.

Dr Gerdts, who runs Broken River Apiary honey business and bee breeding research body Bee Scientific out of Benalla, has been preparing for this moment for years.

She monitors her hives with soapy washes at least once a week, tracking mite numbers colony by colony, and rotating between chemical treatments and organic acids like oxalic and formic acid to stay ahead of resistance.

“Monitoring is just so important,” she said.

“You treat, you knock the mites down, and then you come back, and it's like a wave ... you’ve got to keep watching your numbers.”

But Dr Gerdts said chemicals were only part of the answer.

With a PhD in host-pathogen relationships from La Trobe University and more than two decades working with bees, she has spent years breeding lines of bees with stronger hygienic behaviour and the ability to detect and remove mite-infested brood before populations take hold.

“The whole baseline of the integrated pest management pyramid is genetics, and nobody’s talking about it,” she said.

Behind the mite lurks a second threat.

In every country where varroa has developed chemical resistance, Deformed Wing Virus has followed, causing bees to emerge with shrivelled, useless wings and collapsing colonies.

Australia currently holds Deformed Wing Virus-free status, but Dr Gerdts said that distinction was already under pressure.

While varroa cannot infect native bee species, the virus can, meaning a pathogen that has elsewhere devastated commercial apiaries, could spread into ecosystems that have never had to defend against it.

“The virus and mite combination is sure colony death,” she said.

“Right now, if I find 10 to 15 mites in a 300-bee wash, I'd treat. With the virus included, those bees would be dead before I even got the chance to wash them.”

For Goulburn Valley farmers, the stakes reach well beyond the hive.

Dr Gerdts said that two-thirds of the fruit and vegetables Australians eat are pollinated by bees, with almonds, stone fruit and many vegetables exclusively dependent on managed hive pollination.

Crops like canola and lucerne, staples of the region’s mixed farming landscape, also benefit significantly from bee activity at bloom time.

“We grow at big scales, we grow in monocultures, and the bloom happens for about two weeks,” Dr Gerdts said.

“That’s what we need to be able to bring the bees, put them down, let them do their job.”

Agriculture Victoria said its bee biosecurity officers were providing on-ground support to beekeepers across the state, including surveillance techniques, treatment options and planning advice, as part of a two-year Varroa Transition Program.

Beekeepers who suspect treatment failure or detect varroa mites are urged to contact Agriculture Victoria's Emergency Plant Pest Hotline on 1800 084 881.